View Full Version : How accurate are exposure meters? Not very....
I have been experimenting with light meters, again. Many years ago, we had a long thread on this subject, it was very interesting, lots of good contributions. Light meters are calibrated at one color temperature. So how far off is the readings when the color temperature changes from the Kelvin range it was calibrated at ?
For those who don't shoot chrome film, and are NOT ultra sensitive about nailing exposure, please stop reading here. :-)
Anyway, I took my Gossen 3 Color meter, which has RGB sensors... it produces a Lux value for light intensity based on 3 color sensors. In the old thread, it was suggested that an ideal light meter would read the 3 colors of light, and then produce an EV value... discussions then went into having the meter calibrated for each of the color films...OK, that was really dreamin considering film was dying then, and now.... well.....
I used the Gossen 3 Lux reading as a baseline reading. I converted Lux to EV via a table such as this on Sekonics web site....
http://www.sekonic.com/support/support_2.asp
I took incident meter readings with 4 meters and compared them with the Gossen Color 3 EV value... the 4 meters were...
Sekonic L 608
Sekonic L 208 (very small manual)
Gossen DigiPro F
Gossen DigiFlash (mini meter, new model)
the color temperatures I tested ranged from 2300 to 10k Kelvin. I had readings at almost every 1k color temp interval.
I used the Gossen 3 meter Lux / EV reading as the basis, and compared all the other readings to it. I sorted the results by color temp. and by EV. A value of 0 means the incident meter matched the Gossen 3 Lux value. A value of -.4 means the incident meter read .4 stops below the Gossen 3 Lux / EV value. +.4 = incident meter read .4 stops above the Gossen Lux EV value.
As expected, the results vary tremendously, not just against the Gossen 3 Lux/EV but also vs. each other. IMO this demonstrates something I have always felt...... these meters are at best, "fair instruments", certainly not ideal tools if you shoot under varying light and color temperatures. These test results are all from outdoor lighting, so landscape shooters beware. I consider a .4 stop error quite large from a meter, for chrome film. Add in some errors of your own, processing, etc. Its not hard for your exposure to be off .75 of a stop. Then, as you can see, there is often errors near one stop. (all based on the Lux/EV value)
I was hoping the results would yield some compensation values I could apply to a given meter, when knowing the color temp, but that is not the case, as its a mix of color temp AND EV values that trip up the readings. Of course, maybe the color temp meter provides the most accurate exposure readings. Not sure of this either..... any thoughts?
Regardless of whether the Gossen 3 color meter provides the most accurate exposure readings, the sad finding of this test was.... the meters themselves vary tremendously from each other... often a full stop variance....you can read across the lines, -4 to +6 = 1.0 stop variance.
http://www.pbase.com/image/114793400.jpg
Drew Wiley
9-Jul-2009, 18:14
I have three Pentax digital spotmeters. One is kept as a reference and never used in
the field. All three give exactly the same readings over a wide range. If one differs,
I get it recalibrated. I also had a Minolta spotmeter; it eventually was stolen, but
gave virtually identical readings to the Pentax ones. My internal meter in my Nikon
FM3a is very close to my current Pentax readings. What I discovered was rarely
consistent, however, was gray card values from one brand or even batch of card
to another. That is why spectrophotometers are always calibrated to an individual
ceramic tile which doesn't fade. But as far as the meters I personaly use, I'm
convinced they're very reliable, and I have to recalibrate them less than once a
decade. I have far more accurate custom meters for lab use per se, actually too sensitive for field use; but this would be overkill for general photography anyway.
If there's going to be an error it's a lot more likely to be due to poor judgment on
my part or possibly flare than due to any inconsistency with my light meters.
Sorry if your meters aren't so satisfactory.
> I have three Pentax digital spotmeters. One is kept as a reference and never used in the field. All three give exactly the same readings over a wide range.
Drew, I have other Sekonic meters similar to the 608....guess what, they all read identical to the 608. What does this prove? You are making a wild assumption that if 3 identical meters, give identical readings, than all 3 produce accurate readings. What is the basis of this? Your meters, just like the meters I showed, can only be calibrated at ONE color temperature. So of course, they will all read very similar, they are the EXACT same meter, calibrated to the EXACT same benchmark..... ??? This demonstrates nothing about accuracy over a wide range of color temps and light intensities. That was the finding from this test.
> But as far as the meters I personaly use, I'm convinced they're very reliable,
All my meters are very reliable also.... but the test I performed, demonstrated they all can't be accurate....and if yours was in the mix, it too would be all over the map vs. the Gossen 3 which reads all 3 colors before calc. light intensity. That was the point of the post....
Bill_1856
9-Jul-2009, 19:33
My Pentax digital spot meter came from the factory one stop off (I don't remember if it was high or low -- never got around to having it adusted). Instead, I just just a little Kentucky windage for my Weston Euromaster.
Oren Grad
9-Jul-2009, 21:04
So that's half the equation. Does the effective speed of your film change at different color temperatures?
Kirk Gittings
9-Jul-2009, 22:02
How accurate are exposure meters?
Accurate enough obviously.
Vlad Soare
9-Jul-2009, 22:49
I don't need a perfectly accurate lightmeter. I only need one that's good enough for the job. And from this point of view my Gossen has never disappointed me. As long as I get perfectly exposed slides with it, I couldn't care less about its theoretical accuracy. :)
The same goes for shutters (is 1/125 really 1/125? No, but it's close enough), for apertures (is the amount of light passing through two different lenses at the same f-stop really the same? No, but it's close enough), for the film position (is the film really placed at the exact same spot as the ground glass? No, but it's close enough), and so on.
So that's half the equation. Does the effective speed of your film change at different color temperatures?
Good point. Yes, I think it does.
Ivan J. Eberle
9-Jul-2009, 22:55
I can remember hardly ever shooting a bad chrome with either of my Nikon F5s, which camera had arguably the most sophisticated RGB meter of it's era. Downside was that it ate battery charge like nobody's business. (On a stay-alive remote just sitting there waiting to fire with the meter on but doing nothing else, I never got more than 7 hours out of 8 AAs).
Now after nearly a year of toting around a DSLR to use as a spot meter for my LF color transparency work I'm tempted to go the C41 route to simplify. With NPS 160NC or Portra NC and Sunny 16 I figure my GE DW-58 Selenium footcandle meter would pretty much handle everything between fifteen to dawn and a quarter past dusk.
Scott Knowles
10-Jul-2009, 06:03
Interesting, but it makes the assumption the Gossen 3F is "the" standard for light measurement, which in reality, it's just another light meter, albeit an excellent one, but still relative to reality. If you want a real test, then use a scientific standard for light measurement against all five light meters. Then maybe the results have merit more than a comparative test, and I wouldn't be surprised if even the Gossen meter has an error factor.
> Accurate enough obviously.
For some, yes.... for others shooting in very tight exposure latitude scenes, "obviously", there is a lot of room for error.... If I shot neg film, I wouldn't care the least bit.
> I don't need a perfectly accurate lightmeter. I only need one that's good enough for the job.
Hence why I wrote this below, in the 2nd line of my post....
> For those who don't shoot chrome film, and are NOT ultra sensitive about nailing exposure, please stop reading here. :-)
> The same goes for shutters (is 1/125 really 1/125? No, but it's close enough), for apertures (is the amount of light passing through two different lenses at the same f-stop really the same? No, but it's close enough),
HUH? Are you serious? I am showing how exposure values are off by .3 - 1 stop.... and you think the 10% max. a shutter or apt. is off any given exposure is its equal? .1 stop, vs. 1 stop? 10x difference? I don't see the logic. BTW, I tested 15 of my LF lenses with a shutter tester, and the worst error was 3%, not 10% and that was for one lens, and one f stop only...thats how accurate most shutters are. So I don't really follow your logic..... Whatever......
> for the film position (is the film really placed at the exact same spot as the ground glass? No, but it's close enough), and so on.
GG alignment? Exposure? ?? Anyway, we have something called Depth of Focus at the film plane to protect against small gg/film alignments. We have no equal when it comes to exposure. But this discussion is not about focus....
> Interesting, but it makes the assumption the Gossen 3F is "the" standard for light measurement, which in reality, it's just another light meter, albeit an excellent one, but still relative to reality.
Scott, even if you eliminate the Gossen 3 as the "standard", look at the errors between the meters themselves, that was the point. If they all had very similar errors vs. the Gossen 3, then I would agree, but its obvious, the errors against each other are extreme IMO. This demonstrates at different EV levels and different color temps, the different makers of meters have errors that are not consistent with each other.
> If you want a real test, then use a scientific standard for light measurement against all five light meters. Then maybe the results have merit more than a comparative test, and I wouldn't be surprised if even the Gossen meter has an error factor.
A more scientific test would be nice.... but if you take two new different makers meters, and they read 1 stop different than each other...... the evidence is obvious...they both can't be accurate. Even if the error falls right in the middle, thats .5 stops off per meter.... that's the best case scenario. That's the point.... no need to go to the next level unless you want to track each of the errors vs. a standard. This test identified the meters have much larger errors than most think, period.
And yes, the Nikon did have a "color" meter to evaluate exposure IIRC..... good point... I think that was the the only camera that incorporated such...
> but if you take two new different makers meters, and they read 1 stop different than each other...... the evidence is obvious...they both can't be accurate.
But if you take six, and all of them are different by more than the error margin in their specs and you can rule out that at least five out of six were defective, there must have been some flaw in the test methodologies.
sanchi heuser
10-Jul-2009, 07:41
Hi bglick,
why are some numbers in brackets?
sanchi
Stephen Lewis
10-Jul-2009, 07:42
Intersting exercise, but a couple of observations if I may;
I don't thing it's important that my meter is ultra-accurate, regardless of the standard measured against. It just needs to be consistant.
I'm happy to work to the nearest 1/2 stop, and make adjustments at the processing stage having seen the first sheet. There are too many variables throughout the image making process to be any more accurate. ;)
Nathan Potter
10-Jul-2009, 07:46
bglick has only done a comparison test and not dealt with absolute accuracy. I find the results interesting but not unexpected. As has been pointed out, additional exposure variability results from film response and shutter speed variability.
How did bglick increment the color temperature steps - black body, tungsten filament?
Read by one of the color meters I presume.
My take would be sort of like Gittings comment. I don't care how accurate my meters are as long as they are consistent. Zone tests determine the densities of chromes or negs as a function of meter readings. Grey card exposure gives a chrome at logD 0.9 and negative at logD 0.9 for normal development. Of course experimental stuff is apt to be logD all over the place. I just check meter calibration periodically using bright sun on clear day and grey card to read EV 16.3 and use a paste on arrow on the Pentax meters.
Nate Potter, Harrington ME.
> But if you take six, and all of them are different by more than the error margin in their specs and you can rule out that at least five out of six were defective, there must have been some flaw in the test methodologies.
The accuracy of the Sekonic meters are +/- .1 EV. You mention "flaw in the test methodology". You are missing the point. If a meter is calibrated at one color temp, it should be relatively accurate at that color temp. Which I would suggest they are. But how do they perform at different color temps? No specifications on this....of course not.... cause if the makers provided specifications on how far the meters are off at different color temps, do you think this would help sales? The avg. photog knows very little about the nitty gritty of this stuff, and meter makers want to keep it that way.... hence why i shared this info, which I am starting to regret....
> why are some numbers in brackets?
brackets always indicate negative values. <.5 > indicates the meter read .5 stops BELOW what the Gossen 3 read. From that, you can see the errors between the meters.....from my post above...
the meters themselves vary tremendously from each other... often a full stop variance....you can read across the lines, -4 to +6 = 1.0 stop
variance.
sanchi heuser
10-Jul-2009, 08:05
> brackets always indicate negative values...<
Ok,thanks.
I once tested a broncolor FCM and a Gossen lightmeter.
There was only a difference of 0.1 stops.
And I compared 25 - 30 times under different lighting conditions.
sanchi
Robert Fisher
10-Jul-2009, 08:19
Bill, as mentioned by a previous poster, the F5 that I also used for years had an incredibly accurate color metering system - MUCH, MUCH superior to the 5 and 6 series Sekonics that I use.
Shooting E6 with the F5 was an enjoyable and productive experience.
Perhaps I am not as stupid as I thought - my meters are partially to blame.
Anyway, is there a particular color meter that is considered state of the art?
Thanks for your research and posts!
>How did bglick increment the color temperature steps
As mentioned, color temp came from the Gossen 3 meter.
> I don't care how accurate my meters are as long as they are consistent.
Most meters are consistent..... they will be consistently inaccurate under different color temps. An exhaustive film test under controlled lighting would be an ideal test to determine not only the exposure error, but how the film reacts at these color temperatures. Considering most of the list found my 15 minute test absurd / uncalled for, I can't fathom how the list would react to the sharing of information for an exhaustive film test and the cost of using such expensive controlled lighting and metering equipment. But yes, this would be ideal.
My guess is though, (please note the word "guess"), using a color meter as an exposure meter (assuming the color meter reads Lux) will get you close enough to an accurate exposure reading, at any color temp. This assumes films responses does not alter such. This would explain the excellent success the NIkon had with its built in color meter for exposure....
Sekonic has a new color meter.... it has a film and digital setting for reading color temp, as both react differently. If I were to buy a new color meter, I would gamble on that one, as the color meter takes into consideration (somewhat) how chrome film reacts. Contact Sekonic for more information, and report back if you do....
> Perhaps I am not as stupid as I thought - my meters are partially to blame.
hey Rob, I guess its just me and you who do NOT have PERFECT exposure with chrome film 100% of the time. Most of the list seems to have never have a problem, it appears we stand alone. After 30 years at this, I am embarrassed that everyone else has had perfect success. Oh well, maybe practice does not make perfect.....or, maybe, I sometimes have been fed erroneous data from my meter....nah, impossible...$100 - $500 meters should give perfect readings under all circumstances, even if they are only calibrated and tested at one color temp.... Yeah, so it's my technique always at fault....
> If a meter is calibrated at one color temp, it should be relatively accurate at that color temp. Which I would suggest they are. But how do they perform at different color temps?
We don't know. Or rather, your test does not tell us - it only subjects several light meters to multiple variations in lighting, and assumes that among them only color temperature had any influence on the results.
You did not even maintain a constant change in EV - the figures are jumping all over the place, at a much greater magnitude than the change in K. For a clean test, only the tested parameter would be variable - a constant growth in EV would be the absolute minimum for an amateurish approximative test.
Robert Fisher
10-Jul-2009, 09:08
Bill, I just read the specs on the Sekonic C-500 color meter. Besides the cost ($1,000) it apparently does not read below 2,300K. From a real world film perspective, this is probably not be an issue. It appears that 2000-3000k is the quality of light seen at sunrise or sunset.
Any thoughts anybody??
Bob Salomon
10-Jul-2009, 09:42
Film has latitude. Shutter speeds are within tolerance if they are ±30% of the marked speed. ISO, exposure meters and guide numbers are starting points. They are not arbitrary. You tailor the ISO, the filter factor, the guide number, the exposure meter, the flash meter and the color temperature meter for your personal preferences (if you shoot for your satisfaction) and to your clients expectations if you are shooting for someone.
percepts
10-Jul-2009, 09:56
if a colour meter isn't matched to a particular film then what is the point of your test.
Each colour film has RGB layers but what is the actual wavelength range of those layers? I bet they will not be single wavelengths because if they were, they would remove a lot of colour information from the subject. So does your colour meter work on single wavelengths for each colour and if not what range does it work over and do those ranges match the film RGB ranges exactly. I think not. So what does does your colour meter prove? Nothing. It always comes back to practical evaluation and that is done using ONE meter so that your personal ISO speed suits that meter. If you have other meters which don't give same readings then you have to test those as well. There are no short cuts.
p.s. digital cameras have white balance so why don't light meters?
Bruce Barlow
10-Jul-2009, 10:06
Hmm. All I know from my own experience is that my B&W proofs - made consistently, all with the same exposure, development, etc. - are consistent. They all look fine. So if my Pentax Digital is goofy, then it's accurately reflecting a goofy universe.
"Close Enough for Photography."
I guess I'm missing the practical application of bglick's analysis. What, practically speaking, should we do differently?
Mark Sawyer
10-Jul-2009, 10:06
I find my inaccurate meter compensates for my faulty shutter speeds. And my overcompensation for reciprocity failure usually makes up for forgetting the bellows extension factor. I think I'm finally perfecting my technique...
BrianShaw
10-Jul-2009, 10:16
Doesn't the K-factor also influence the reading a meter might give. Some manufacturers seem to clearly state their K-factor; others seem to not.
but... too much scientific analysis ruins the fun for me. Somehow I seem to get good, accurate, and consistent negs despite using a collection of potentially inaccurate, imprecise, and poorly calibrated meters. Perhaps I should have taken the "don't bother reading" option offered in the OP ;)
> You did not even maintain a constant change in EV - the figures are jumping all over the place, at a much greater magnitude than the change in K. For a clean test, only the tested parameter would be variable - a constant growth in EV would be the absolute minimum for an amateurish approximative test.
Sevo..... just to clarify this post...
1) I was not paid by you, or an outside source to run this test. This short test was to confirm a suspicion I always had.
2) The results of this short test, speak volumes about the variance in light meters, plain and simple. Is this a perfect test? Hell no, but it proves an obvious point, their is huge errors between different light meters. Certainly far above the +/- .1 stops advertised.
3) The information I shared in this post was as a courteousy. I am sorry if I did not spend weeks and thousands of dollars producing the level of information you would classify as a bear min. for even an amateurish study. You are welcome to do such, and share with the list. Or if you want to fund the study to be sure it meets your min. amateurish standards, just send me $5k and I am capable of performing such.
> and assumes that among them only color temperature had any influence on the results.
Sevo, this claim was never made, the variance in readings in this small sampling can be a result of light levels AND/OR color temp... my guess is, it's both. Accept the data for what it is, draw your own conclusions.
Rob, I would say the number of times landscapes will produce color temp below 2300 is is very rare. So, I would not be concerned about it. If you take this route, run a test with 35mm chrome film against an exposure chart....compare with an exposure meter. If you do such, I would understand why you would not post the results to this forum, but I would sure appreciate if you shared the results with me off list....
> You tailor the ISO, the filter factor, the guide number, the exposure meter, the flash meter and the color temperature meter for your personal preferences (if you shoot for your satisfaction) and to your clients expectations if you are shooting for someone.
1) I never once heard a client suggest a specific tailoring of these variables, they want a properly exposed image...
2) Considering most pros know very little about this, I doubt the avg. photog is tailoring for these issues. The assumption is, exposure meters are accurate. Now that most of the world is digital, the results are right on the screen after capture, not a huge issue anymore.... except if you shoot 8x10 in the field and the results are not seen till weeks later...
the one exception to this rule is the studio shooters who spend days tweaking their tools. This forum is not heavy into studio shooters, hence my comments.
> if a colour meter isn't matched to a particular film then what is the point of your test.
Argggggg..... I may have to remove this post. As mentioned several times above, this test demonstrates that exposure meters vary tremendously in exposure readings over different color temps and/or different EV values. That's it! Get it? Nothing else, forget film.... this is about exposure meters. If one meter reads 7.5 EV, and another reads 8.5 EV, they both can't be right.... get it? It's that simple !!! They may each be off by .5 stops, or one could be off a full stop, and the other nutz-on. Or it can be even worse... This 15 minute test did not determine where the errors lie, it only exposed the fact the errors exist.... make sense now? OK?
> So what does does your colour meter prove? Nothing.
thats correct, but what you fail to realize is, I never suggested the color meter was a reliable standard to test against. So once again, lets try in CAPS this time....
THIS TESTS DEMONSTRATES THAT EXPOSURE METERS, FROM DIFFERENT MANUFACTURERS, RECORD VERY DIFFERENT EXPOSURE VALUES UNDER DIFFERENT COLOR TEMPS AND EV RANGES!
Now, is this clear yet?
> I guess I'm missing the practical application of bglick's analysis. What, practically speaking, should we do differently?
Bruce, I am not suggesting anyone do anything different. I tested 4 meters and offered the results to the list, which turned out to be a huge mistake. What you do with the data is your business. If you have perfect exposures on every shot with your film and meter, then you have nothing to be concerned about... why would you change anything?
I am not suggesting any changes to exposure techniques based on this test, because I don't have sufficient data to suggest such, I simply shared the results to demonstrate the errors..
All I can say is, it's insane to expect exposure meters to be within +/- .1 EV (what their specifications state) over a wide range of color temperatures and EV values. They can often be a full stop off. Whether this is of concern to you as a photog. is personal preference, often based on the type of photography you do, and how picky you are about your results.
too much scientific analysis ruins the fun for me. Perhaps I should have taken the "don't bother reading" option offered in the OP
yep, you got that right..... hence why I put that in the 2nd line of the post.... but, at least you were one of the few who comprehended and acknowledge this, so Kudos to you Brian....and congrats on your great exposures. And you are right, if you have having fun, and happy with your exposures ignore these type posts....
In my case, I often can spend thousands of dollars getting to a location for a shoot, and while bracketing is the ultimate solution to this issue, with 810 it can be quite costly.... so I try to gain as much knowledge as possible to increase my chances of success..... I know, call me crazy, ..... I just can't help myself....
percepts
10-Jul-2009, 10:26
All I can say is, it's insane to expect exposure meters to be within +/- .1 EV (what their specifications state) over a wide range of color temperatures and EV values. They can often be a full stop off. Whether this is of concern to you as a photog. is personal preference, often based on the type of photography you do, and how picky you are about your results.
What did you expect to learn from your test? It seems you thought these light meters are scientifically calibrated devices. They ain't. Once you know that then you will understand the futility of your test. Get it?
> What did you expect to learn from your test?
It's called "confirmation" Percepts.... get it? I was confirming my suspicion. Or maybe the sensible position is, accept suspicions, don't confirm... that might be your style....
> It seems you thought these light meters are scientifically calibrated devices.
It seems you still have not comprehended my post. I knew these meters were only calibrated and tested at one color temp. Hence why I ran this simple test. I knew there would be errors at different color temps and EV ranges, but how great would the errors be ? That's what the test demonstrated, get it now?
> They ain't. Once you know that then you will understand the futility of your test. Get it?
You are right, they "aint" scientifically calibrated devices. That alone would not answer the question of, how far do these meters drift when they are used outside their calibration range.... get it now?
Let me know if you are still confused....
Jim Michael
10-Jul-2009, 10:38
What I see as potentially useful information from your tests is that, if you photograph under varying color temps (e.g. indoor incandescent, outdoor daylight, etc.) then it would be a good idea to calibrate your process for each of those general scenarios.
.
Thanks for being the "voice of reason" Jim, yep, that's the sensible conclusion to draw from this....or at least be aware of such.
Of course if you shoot neg film , you have greater exposure error capacity, and it might be overlooked, specially if you bracket....
But regardless, a spritz of common sense sure was refreshing here, thanks!
Dan Fromm
10-Jul-2009, 11:26
I wonder what the George of Quality Light Metric would say to all this, besides "Your meters need to be calibrated. Send them to me."
Bill there's ample evidence that many meters are delivered off calibration. And I've never got a iused meter that was trustworthy. OTOH, the on-board meters in my humble low-end Nikons have only rarely steered me wrong.
I once took a used Lunasix to the guys in Springfield, NJ, who explained to me what's required to test a meter properly. Bill, I'm not sure you have it. I know I don't. I also know that when both were freshly calibrated, my Lunasix 3 (Bogen did it) and Master 5 (George at QLM did it) didn't often agree closely, whether reading incident or reflected. Funny thing is that both gave me ok E-6s. They still don't agree closely. And when I don't present them with a difficult situation both still give me good E-6s, be it at high noon or at dawn/dusk when the light is dim and cold.
Cheers,
Dan
> Bill there's ample evidence that many meters are delivered off calibration.
And I've never got a iused meter that was trustworthy.
The 608 was sent in for calibration recently, it was nutz-on.... the other meters were all brand new.... So none "used" except the 608 which I bought new and had rechecked.
> I once took a used Lunasix to the guys in Springfield, NJ, who explained to me what's required to test a meter properly. Bill, I'm not sure you have it.
Dan, once again, I did not "test" these meters as you suggest, instead, what I performed was a "relative comparison" between the meters, nothing more. The results demonstrate, the errors between meters vary greatly based on the type and manufacturer over a wide range of color temp and EV. It's that simple. If you threw some more money at this, we would learn more..... I spent 15 minutes on this test, and about an hour so far trying to explain the results on this forum. So far, Jim, Mike and Rob, "get it".... consider this post a "be aware of" type post. Don't consider this post a "hardcore scientific study that will be published in peer reviewed journals". It's amazing I have to even mention this.... It's no surprise many great contributors that used to be on this forum dropped out long ago.
> Funny thing is that both gave me ok E-6s. They still don't agree closely. And when I don't present them with a difficult situation both still give me good E-6s, be it at high noon or at dawn/dusk when the light is dim and cold.
I think you summed it up good here.... when the meters are used close to their calibration color temps, they are accurate enough, agreed. You can see this from test results at 5370 color temp....all meters were within 1/3 of a stop, not bad. Its when the meter is used outside of their calibration zone, the error variances becomes much greater. Notice the 7750 color temp reading, 1.3 stop variance. Of course, this is just the variance, the true error can be greater than this....we don't know without a reliable standard.
NewBearings
10-Jul-2009, 12:31
bg -
How do you print your chromes after processing?
Your numbers don't seem so far off (color) that some minor tweaks in PS would not remedy. What am I missing?
As far as the amount of light read I see more concern.
When my 13 year old Sekonic final fell apart I exchanged it with an upgrade for a new (at the time) L-508. I tested it against every make and model I came across in everything from ambient daylight, to fluorescent to studio flash. Generally I found a difference ranging from -0.4 - +0.8. The current setting on my meter is biased @ -0.8.
BrianShaw
10-Jul-2009, 12:35
The results demonstrate, the errors between meters vary greatly based on the type and manufacturer over a wide range of color temp and EV.
Did you normalize for (or even checked for) differences in K factor between the meters... or is there a reason why nobody addressed this known source of variance, even after I mentioned it earlier?
Additional question: does anyone know off-hand what ISO, NIST (or any other) standard specifies photographic light meter calibration? I know that scientific photometers and industrial light meters are calibrated to some standard but don't know if they are the same or what the acceptable range mignt be.
Drew Wiley
10-Jul-2009, 12:38
Let me clarify. I check all three meters simultaneously, pointed at different gray values
AND different hues of a Macbeath chart, under identical lighting, using a Minolta color temp meter is necessary. They match. Does that mean the linearity with all hues is
a straight curve. Of course not. You have to understand the spectral sensitivity of the
sensor in the particular brand of meter. But all three meters are predictable in exactly the same manner. If not, it's time to recalibrate. I also have a lab meter about hundred times more accurate than these Pentax meters. It is programmed to read in density units rather than EV values, so isn't for camera use - but if I know how to program and work with something like this I damn well understand what I'm talking about with a handheld meter. I can't speak for the quality control of Pentax meters in current production, since I haven't bought one in the last 15 years; but I can state that when Quality Light Metric recalibrated the ones I have used, the result precisely matched the linearity and EV value of my unused control meter at its original factory settings.
> but if I know how to program and work with something like this I damn well understand what I'm talking about with a handheld meter.
Drew, what you have demonstrated is that 3 identical meters, give identical readings when exposed to the same color temp and EV Range......right? How is that relevant here? I still don't understand your point as it relates to this post. My post is about different meters under different lighting conditions. Your post is about identical meters under different lighting conditions?
As I mentioned, I have another digital Sekonic that is nutz-on vs. the 608, never more than .1 stop difference. That demonstrates to me, that Sekonic meters of the same type (digital) have tight manufacturing tolerances and all perform relatively close under most all lighting conditions. It gives no indication the readings are accurate vs. the other meters I tested. does this make sense?
Brian, if you describe your K factor more clearly, I will try to respond.... and there is no industry standard for photo meters... at one point, the german meters were calibrated at 5500K daylight, and the Japanese calibrated to ~3000k ...... but, supposedly, now, Sekonics are calibrated to daylight as well.... not sure this is true, its based on speaking with Mamiya USA rep, can't find anything in writing....
NewBearings, sometimes I don't print my chromes, the chrome itself is the final product....other times they are drum scanned and corrected. Interesting how you bias your meter by .8 stop..... One of the reasons I wanted to run this test, was to see if there was a simplified biasing method that would help compensate.....but as you can see, as color temp changes, the bias would have to change directions as well. Again, this is based on the Lux value readings of the Gossen 3, which we all agree is not a bona fide standard, but regardless, i was curious of there was any trend I could latch on to, then maybe I would have ran another test....
NewBearings
10-Jul-2009, 14:06
Keep in mind, unless you are doing copy work, "accuracy" may be a subjective determination. Most gear requires some "calibration" and fine tuning. But this is often based on your own system and -subjective- needs.
Drew Wiley
10-Jul-2009, 14:12
Somewhere buried in my archives is a graph by Pentax showing the spectral sensitivity
graph of their silicon sensor. It peaks close to the maximum sensitivity of human vision. Therefore a reading from a green surface of grass, forest, etc easily
substitutes for a gray card reading or gray rock etc. In the real world you simply get
used to your meter. My very first camera was a very early Pentax with a exterior
coupled CDS meter, and I don't think I ever botched an exposure, even with Kodachrome. My apparent luck at the moment is that the sensors in my manual Nikons
seem to behave very similarly to the cells in my handheld Pentax meters, apparently due to a similar mentality and similar silicon cells in use (also similar vintage Japanese
mfg). There obviously has been an attempt with the modified Zone VI meter to correct for certain color inadequacies, which has been discussed many times on this forum. But color temp per se has far less to do with this than spectral response and what kind of standard you take as a reference. Sensitometry is a subject in its own right. And it's impossible to make a meter that's completely color-blind; and I don't
even believe it would be smart to make all meters behave exactly the same, because
they are engineering for a different range of applications. Choice is important. But
to call them unreliable for color readings is absurd. Color tranny film is fussy stuff;
we'd all go broke if our meters were unintelligently designed.
> unless you are doing copy work, "accuracy" may be a subjective determination.
The first step in proper exposure is to get an accurate light meter reading.... if your starting point is 1 stop off, your starting point is off... more errors after this, (processing, flashes, etc) has no bearing on the fact you are starting with inaccurate data.
> In the real world you simply get used to your meter.
Do you ever notice how grass always looks green, regardless whether the color temperature of the lighting is 3000K or 10,000K? If grass always looks green, and colors always look true (our visual system compensates for such, drawing on its reference banks), then how do you "get used" to your meter? How do you know when your meter will produce a certain error, if you don't know yourself the condition exists? Our eyes are the worst judge of both color temp and light intensity, as we have too many involuntary compensations occurring. I have shot under many situations where I swear the color temp is near 6k, and yet, its 9k, been fooled hundreds of times.
Trying to notice a 1 stop change in light is not easy for our visual system. Sunny 16 is great, if you have NOTHING else to work with....but I have been out mid day and swore Sunny 16 would apply, and yet, I have had readings anywhere from 14 to 17 EV. This is the value of meters.... (preferably accurate ones)
> But to call them unreliable for color readings is absurd.
I marvel you can say this, after seeing the test results above. Unless of course you don't believe them, then I would fully understand your position, otherwise, I don't get it. These meters have large variances at different color / EV ranges. Even the manufacturers would probably admit to this.
> Color tranny film is fussy stuff;
hence why I posted this, now somehow, you are supporting my efforts?
> we'd all go broke if our meters were unintelligently designed
Go Broke? why? How about..... our exposures will sometimes "not be as accurate as we would like"..... this seems like a more reasonable assertion from the data I provided, vs. your exaggerated claim of..... "we'd all go broke?" ???
Unintelligently designed? No way, modern meters are very intelligently designed. Heck these companies have had 80 years to perfect the meters. The problem arises, when you try to use a meter that is calibrated at only one color temp, then attempt to use it at "many" color temps. The manufacturer offers no assurances of their accuracies at "non-design" color temps. This is not stated anywhere in the sales brochure, but its the reality of these low cost exposure meters. (low cost, vs. more scientific grade equipment)
Drew Wiley
10-Jul-2009, 15:30
Color temp has little to do with it, unless you're clear out in left field at the extremes.
Color temp varies all the time unless you're under studio conditions - that's why they
invented programmable color temp meters in the first place - but we rarely use them
except in commercial photog because we like what we see; otherwise we just add a
cc filter appropriately. Some photocells have a fairly symmetrical curve of response.
You can either plot this (nobody does) or get used to it. Once you place one of these
into a camera things get complicated, since cameras nowadays try to do everything
for you. With view cameras we generally take handheld readings, so get to
understand the meter's sensitivity per se better, at least until you run into things like
flare and bellows extension. Color trans film has very little lattitude. I shoot the stuff
in 8x10 - can't afford to be guessing. Half-stop error, no way! But for one scene I
read some grass, next shot in the desert -no grass - I read a brick red rock. How
come both readings work? Because the meter is predictable, reliable. I know through
experience or testing that it's more sensitive to certain colors than others. No
difference with an enlargement meter except that you can keep the color temp constant (with certain kinds of light sources). Color temp is a different variable than
color sensitivity. At a certain point these two variables transect; but most modern
meters aren't that fussy about a thousand degrees K here or there. Reading a bright
red versus a saturated blue, however, might drive one nuts, unless you already understand the bias. Spotmeters behave different than indicent meters, and so forth.
But there is NO ABSOLUTE REFERENCE POINT. There is no such thing as a "true"
reading because, in the field at least, conditions are always changing, and different
people use meters in a different manner. Light meters are not spectrophotometers!
Stick with the brand which works for you and calibrate accordingly.
BrianShaw
10-Jul-2009, 16:11
Brian, if you describe your K factor more clearly, I will try to respond.... and there is no industry standard for photo meters...
Sure. I can do that. It seems to show up in lots of conversations and publications regarding meter calibration/accuracy.
http://www.largeformatphotography.info/articles/conrad-meter-cal.pdf
see page 7
http://dpanswers.com/tech_kfactor.html
see Section 2.
http://photo.net/medium-format-photography-forum/007XcE
see Severi Salminen , Feb 27, 2004; 06:08 p.m.
Also see:
http://en.wikipedia.org/wiki/APEX_system
I know that my Weston meter states on the plate K=1 but I haven't seen such data about other meters, nor do I know if differences make any appreciable difference.
Re: photo meter standards... I know the photometer and goniophotometers I used way back in what is almost a prior life were calibrated in accordance with a NIST standard. I believe had something with the reflectance of calcium carbonate. I recall having a "calibration standard" that looked like white rock that we calibrated our instruments with prior to doing studies. Other than that, my memory is vague. I can still recall the calibration sticker on the PhotoResearch light meter that assured traceability, and I still remember writing big checks for that calibration. How that relates to photgraphic light meters I can't say, hence the question.
> Color temp has little to do with it,
HUH? Color temp has everything to do with it.... did you see the results at near daylight vs. 9k, as I explained in my previous post above?
> Color temp varies all the time unless you're under studio conditions - that's why they
invented programmable color temp meters in the first place - but we rarely use them
except in commercial photog because we like what we see;
It doesn't matter what we see, it matters what the film sees....
> With view cameras we generally take handheld readings, so get to
understand the meter's sensitivity per se better,
Can you explain how one gets to understand their meters sensitives? Our eyes are terrible at estimating EV and color temp readings...did you read my previous post?
> but most modern meters aren't that fussy about a thousand degrees K here or there.
did you see my findings in the original post ?? How do you draw this conclusion?? Based on what? At least I provided some test data to demonstrate otherwise...
> Reading a bright red versus a saturated blue, however, might drive one nuts, unless you already understand the bias.
What if you are reading the light source itself? How do you understand the meters bias, when your visual system can not read color temp?
> But there is NO ABSOLUTE REFERENCE POINT. There is no such thing as a "true" reading because, in the field at least, conditions are always changing,
There is a true light level reading at a given point in time - the moment you press the exposure meter button! IF there was no reference point, than explain how a meter is calibrated? Of course there is standards..argggg... Of course conditions are always changing, that's why you keep taking new readings?
sheeesh, I am ready to surrender.... looking for white flag....
BrianShaw
10-Jul-2009, 16:23
bglick, here is what I was trying to recall re: standards. I thought I saw them before and just found them again. Do you know anything about them; do they impact your discussion?
ANSI PH3.49-1971. American National Standard for general-purpose photographic exposure meters (photoelectric type). New York: American National Standards Institute. After several revisions, this standard was withdrawn in favor of ISO 2720:1974.
ASA PH2.12-1961. American Standard, General-Purpose Photographic Exposure Meters (photoelectric type). New York: American Standards Association. Superseded by ANSI PH3.49-1971.
Hi Brian, thanks for the clarification..... since the Adams days, the K factor term has been more commonly called "meter reflectance factor"... but I could be wrong.... I rarely see the K factor term used much these days...regardless, it's 6 of one, half dozen of the other....
First, I hope it was obvious to everyone, I took incident readings of the light source itself, the sun. I fired all 5 meters within a few seconds, then recorded the values after they were fired to avoid any delays in taking the readings. To be clear..... I WOULD HAVE NEVER POSTED MY FINDINGS IF THESE WERE SPOT METERS READINGS !
The reason is obvious, as stated by the some of the nice links you provided. Reflectance readings vary between meters, as each maker seems to have secretive reflectance values. Many years ago, I once tried to match up my Pentax spot and my Sekonic 778 Spot, they were more than a stop apart at all times. I researched this as hard as I could, and could not come up with the exact reflectance values each meter used. Without this information confirmed, you can not ascertain if a meter is not calibrated, or its reading is accurate, but it displays EV information based on a different "assumed" reflectance value of the target. This is why, I only use spot meters when in a jam... whenever possible, I always read the light source with incident readings...from there I can deduct what I need to know from the shadows through the spot meter (looking for delta EV values), disregarding the nominal readings.
As for the standards of the light meters, no, I am not familiar with the ANSI references you provided. For incident readings, a photographic light meter such as my 608 correlates very well with my foot-candle meters I use for my day job. This assumes, the color temp of the light source is ~ 5000K for the Sekonic. Photographic light intensity units, EV's, are directly related to Lux and Footcandles.
And to be clear, I am not trying to prove the accuracy of the meters in this test. They all proved relatively consistent when at the design color temp. The purpose was to determine how large the errors will be between meters under varying color temp conditions. It is quite obvious, they all react very differently. More than I would have liked to have seen. Again, at least for color chrome film....negative film can absorb these type errors. I strongly believe that Nikon shifted to a true color compensated exposure system as most pros shot chrome film, and they saw this as a valuable feature to better nail exposure on chrome film in all lighting conditions.
If I had the time and energy, and a light which I could easily control the color temp and light intensity (possible with filters).... i would run a film test with my favorite chrome films.... I would record the color temp, incident reading, Lux reading and then bracket the grey step chart.... then analyze the results, and create a more reliable protocol to correct for the incident meters spectral response. Or, it's possible the Color temp Lux values by themselves would be close enough to accurate, where it would serve as my new incident meter.... only testing would provide these answers...
Since my exposures are pretty damn good 90% of the time, its a lot of work for that 10% :-)
Scott Knowles
10-Jul-2009, 17:09
Scott, even if you eliminate the Gossen 3 as the "standard", look at the errors between the meters themselves, that was the point. If they all had very similar errors vs. the Gossen 3, then I would agree, but its obvious, the errors against each other are extreme IMO. This demonstrates at different EV levels and different color temps, the different makers of meters have errors that are not consistent with each other.
A more scientific test would be nice.... but if you take two new different makers meters, and they read 1 stop different than each other...... the evidence is obvious...they both can't be accurate. Even if the error falls right in the middle, thats .5 stops off per meter.... that's the best case scenario. That's the point.... no need to go to the next level unless you want to track each of the errors vs. a standard. This test identified the meters have much larger errors than most think, period.
But you also assume the other meters are representative of that brand and model, and they're really just a sample study, and not much more. I suspect there's considerable variation within each brand and model because it depends on the age and use of each one, and if/when they were checked and calibrated.
If all you're saying is they're all different, ok, point proven, they're all different including the Gossen. It still doesn't establish which if any are accurate and over what light conditions. That's where the reference standard is important.
In the end, it's an interesting study but only so far as the light meters you have and used in it, just a sample comparative study, but not one to draw conclusions outside of the obvious which you've proven, your light meters are all different.
Every year I take all (13) my old Minolta manual focus cameras out, add new batteries and do a similar study, comparing light meter readings with Sekonic L-308b and L-358 light meters. I'm only looking for anamolies, and almost every year they're all within 1/3-1/2 f-stop of each other and the Sekonics. That's the whole value of the test, find any errant cameras.
For a short term study at work (USGS) we planned to install some small (then $100) pyranometers (measuring insolation) at gages around Western Washington. The first thing we did was run all of them against a NBS standard pyranometer to establish the range of each and the range of all of them so we could understand the data.
Otherwise any data would be meaningless outside of a ballpark value. That's what you have with your study, a sample ballpark study and of little value outside itself for you and your light meters. Sorry, but that's what it seems to me.
> If all you're saying is they're all different, ok, point proven, they're all different including the Gossen. It still doesn't establish which if any are accurate and over what light conditions.
BINGO! That's all I have been saying, about 8x now :-)
> just a sample comparative study, but not one to draw conclusions outside of the obvious which you've proven, your light meters are all different.
Well, not only are they different, this demonstrates they all can NOT be accurate, that is the KEY point. yes, its a can of worms, but the purpose of this post was to show the can, the dirt, and the worms exist :-)
> That's what you have with your study, a sample ballpark study and of little value outside itself or you and your light meters.
Of little value? This simple test demonstrated that any one of these meters can be .8 - 1.5 stops off, under certain color temps / EV ranges. I have clearly identified this, something that was not known previously. Of course, I don't know which meters are accurate at all these different readings, that would require a more extensive testing.
But most studies start with the path of least resistance first......i.e. start with simplified tests to demonstrate a problem actually exists before going to more in-depth studies. This simple test demonstrated that exact point, so I would strongly disagree with your assertion there was little or no value to this finding. It was well worth the 15 minutes. But the 2 hours wasted on this thread I am starting to question my sanity on....
Ivan J. Eberle
10-Jul-2009, 17:45
No doubt that some motivated geek could've gutted a beater F5 to mount the meter and display in an Altoids tin for you in the same amount of time.
Ivan, that is actually a good idea..... potentially beater F5's may have a 2nd life after film :-) hmmmm........
Ivan J. Eberle
10-Jul-2009, 18:12
Consider too that with Nikon DSLRs also using RGB metering these might be seen as a metering, capture and instant-proofing system, prior to committing that image to a big and expensive sheet of film. (It's been working well for me in 4x5 the past year. Doubt I'll be buying an incidence meter after this thread, myself.)
Ivan, very interesting, what DSLR Nikon models have the RGB metering?
Robert Fisher
10-Jul-2009, 19:43
Bill, here you go
http://www.imaging-resource.com/PRODS/D3/D3A5.HTM
and
http://imaging.nikon.com/products/imaging/technology/scene/14/index.htm
Interesting Rob......well, maybe this might be a smarter buy than a Sekonic Color meter... if you put a diffuser over the lens, it may serve as the ultimate incident meter.... It seems the new soon to be released D400 would be a nice offering, as it appears to be a direct competitor to the Canon 50d, so maybe $1k and one hell of a camera
or for $400, it appears the D60 has the same color RGB exposure metering system? hmmmm....
Ivan J. Eberle
10-Jul-2009, 22:03
My D200 actually works better for this transparency metering and proofing task than my D300. It's easier to use with a base ISO of 100 and also a low setting of ISO 50 (Astia, Velvia) and also has about the same dynamic range. The D300 exceeds the DR of E6, has a base ISO of 200 (though it's got a much better CMOS sensor for high ISO work).
Meters in certain MF cameras like my Pentax 645N also being so good as to rarely blow highlights on a transparency (Matrix-like 6 cell Multi-segment, and spot) coupled with the reality that very big prints can be made from 645 via hybrid processes... has recently got me to thinking I'll stick with it in MF, but soon abandon transparencies in LF to go with Portra NC and NPS160. Figure I'll not miss the fussy metering in fast-changing light too much.
Drew Wiley
10-Jul-2009, 22:19
All you have to do is to look at the published spectral sensitivity graphs for various
color films to realize that not only do these films differ from one another, but that
none of them has a perfect color response. Digital receptors aren't perfect either.
That's just one reason why it's impossible to build a "perfect" light meter. You'd have
to design a different one for every type of color film, with linearity matched to every sensitize layer and idiosyncracy involved. Something which did this would
probably be the size of a Volkswagon. Any of us who have worked much with
tricolor meters, spectrophotometers, or tricolor printing understand that this
is a very complex problem. Even if you could design something portable and reliable
enough, would anyone build and market it? Or would you get any higher percentage
of usable exposures than with a meter design of thirty or forty years vintage?
Probably not, because when most of us botch an exposure, it's due to something
other than the meter!
Ivan J. Eberle
11-Jul-2009, 07:22
Perfectly predicting the correct exposure value may never be 100% reliable-- but at something like $10/pop for a sheet of 8x10 color transparency film nowadays, it doesn't take a lot of wasted film to motivate one to improve upon a meter or metering regime if it can be improved.
Could somebody market it? Perhaps it's closer to hand than we think if we're stuck in some mindset of "tradition".
Killer app for an iTouch, iPhone (or my Blackberry Storm) for a LF photographer: a $9.99 download that matches the camera phone's spectral and DR response to various film types, and displays a histogram. (I'd pay more-- a lot more!)
BrianShaw
11-Jul-2009, 08:39
This assumes, the color temp of the light source is ~ 5000K for the Sekonic. Photographic light intensity units, EV's, are directly related to Lux and Footcandles.
Since my exposures are pretty damn good 90% of the time, its a lot of work for that 10% :-)
I doubt this will affect any of your disucssion but I saw some data in the IHS Engineering Database that indicates that industrial light meters are calibrated at a color temp about 3800 deg. (I'm writing this from recent memory... but I still might be off a few degrees.)
The relationship between lux/footcandles and LV/EV is often provided in the light meter manuals... as you already know. It is amazing that so few people understand that there is even a relationship between the engineering values of light measurement and exposure recommendation -- almost to the point of thinking a photographic light meter is a magic wand of some sort.
Re: the last 10% (of this and almost any other topic... it is hardly worth sweating over most of the time. I, too, can attest to that! :)
Drew Wiley
11-Jul-2009, 09:15
You'd need to develop three parallel spectro programs fed off a beamsplitter, then
come way to calibrate each channel. Last time I talked to an engineering co capable
of this they thought it would have to market in the $6000 range. But the real problem is that you'd have to sell thousands of the things to offset the cost of
miniaturizing the components. Probably the closest thing you'll ever see is going to
happen in the world of DLSR's, which some of you have already noted as alternative
to light meters. R&D goes after money, not what's hypothetically possible. When my
wife worked in Biotech she operated a trade secret spectrophotometer which filled
a small room. It cost six million bucks, mostly I suppose for the proprietary software development. The science is there, just not the incentive or potential market. Tricolor meters like are being described on this thread are stone age by comparison to what's now technologically feasible.
Ivan, thanks for being the voice of reason here. You are soo right, the goal is, to improve our chances of success in tricky lighting conditions when shooting expensive sheet film. While Drew is right about matching each meters spectral response with each films spectral response to really hone in on success.... in the end, this comes down to a question of degree. IOW, if this Nikon metering method reduces errors in tricky lighting from 1.5 stops down to .3 stop errors, I think most of us would consider it a total success. Thanks for the tips on the Nikon D200. With a diffuser filter over the lens, I think it would make a great incident meter also....
Also, I too have adapted your concept of using Neg film when I am not forced to shoot trannies. For a lot of LF newbs who are just starting out, and who desire to shoot color trannies, I always suggest to them, jump up one format size (4x5 to 5x7, or 5x7 to 8x10) and shoot Neg film, your life will be so much easier. This assumes the film will be scanned before going to its end use. The jump up in the format size will compensate for Neg films larger grain and lower resoution vs. trannie film. It's pretty hard to improperly expose Neg film.
In my case, often I shoot trannie, 35mm and 120, 4x5, 8x10 and the film is processed and goes directly in stereo viewers, I have to get it right....when viewing the film, that 1/2 stop of under / over exposures is very frustrating....
Ivan, it seems the D60 has a new RGB metering system vs. the D200, sort of next generation.... would you recommend the D60 ?
Also, do you think the D200's sensors responds the same as trannie film? Seems like a great tool...?
>You'd need to develop three parallel spectro programs fed off a beamsplitter, then come way to calibrate each channel. Last time I talked to an engineering co capable of this they thought it would have to market in the $6000 range.
Drew, if you followed the links Rob offered above, you will see this is exactly what the Nikon color metering system does. Considering they sell hundreds of thousands of cameras, and have been making this color metering system for years, (starting for use with trannie films) the cost of the R&D and the product components itself has been beaten down to consumer price levels. This is the value of Ivans and Robs contributions.
So there is no reason to custom engineer a $10k solution for something Nikon has spent 15 years perfecting and available off the shelf. If you haven't read Robs links, I suggest you do. As for the spectral response of each trannie film, I think most all of the trannie films responses are close enough, that when combined with this metering system, it will remove any large exposure errors traditional meters create.
Finally a thread has a happy ending... glad I did not bail as my instincts kept telling me to.....as this thread took the normal course for the LF forum...... badger the OP, mis interpret the OP, mis quote the OP, sarcasm, etc. etc. This explains why many of the valuable contributors left this forum long ago.. Thanks Ivan for wading through the repetitive responses of this thread, to contribute a very useful suggestion.
Ivan J. Eberle
11-Jul-2009, 11:06
bglick,
Can't say about the D60 but thanks to some of the Nikon links referenced above, it's confirmed that all the Nikon DSLRs since the D2X are using RGB meters.
Exactly what the DSLR Matrix metering algorithms are doing with that information after the fact is perhaps different in digital than what the film camera ones do. The DSLR Matrix algorithms seem to expose to the right in backlit conditions, and you can often but not always recover the highlights in PP (if you shot it in RAW, that is).
But obviously that doesn't work with transparency film. All I need or want it to do is not blow the highlights, and let the other values fall where they may. The F5 algorithms seem to get this right. (Pentax Multi-spot or whatever they called it on the P645N seems slightly biased in the other direction for print film, exposing to the right much like a DSLR regime).
So what I'm most confident using on my DSLR as a metering tool is the spot meter (no algorithms involved. CW probably doesn't compare the scene to 20K others in the memory banks, either). I've heard some argue that Nikon spot metering is looking for a 12% reflectance value instead of 18%. No matter to me as I am getting excellent exposures with the spot metering as long as I can find something middle toned. (Snow might call for incidence, sometimes hard to find a middle gray value in these settings. Reflectance off snow calls for +1 to +2 stops of compensation and I find it varies a lot with the specularity of the ambient light). High and low key are where having the instant feedback of a histogram helps. The D200 is good for this use because the DR is similar to Velvia (not as wide as Astia). It's possible that this is less than 100% reliable as the histogram may be coming off the .jpg and not the RAW, after compression. IDK for sure but this has been a topic in earlier threads.
DSLR sensors, of course, have the advantage of better quantum efficiency and no reciprocity failure. Calibrating this all precisely to a specific emulsion is something I've still not done. What I can say is it's been working well enough out to the 4 second range with my 4x5 and "Mississippi one, Mississippi two..." and Fujichrome regime. If I were doing 2-shot stereo slides, I might also have to tighten up that timing system somehow (although after many years in the wet darkroom, I'd doubt I'm as much 1/3 of stop out of whack with it).
Film is still relatively cheap for 4x5. When in doubt, I bracket 3 exposures, 2nd and 3rd being over and under 1/2 stop. Occurs to me with such good grain-free results I've gotten pushing Astia 100F, that I might as well take the exact same exposure X 3, develop the first in my Jobo, and push/pull the first developer based on the results and apply it to the next two. This wouldn't work nearly as well for Velvia 50, but it's definitely an option with Astia. Too, if the first was spot-on, I'd have 3 identical good copies for distribution. (Might this work as well for your stereo use?)
> Exactly what the DSLR Matrix metering algorithms are doing with that information after the fact is perhaps different in digital than what the film camera ones do. The F5 algorithms seem to get this right.
I was thinkin the same thing after my last post...the F5 was all about trannie film, I think it might have a better chance of success for this application, as reading the light is only half the battle....what the camera does with that light reading is dependent on what it exposing to...and as you suggest, the algorithms in the F5 are probably best suited for chrome film vs. the DSLR's. Exposing to the right is critical in digital, not so true with film, and we don't know what the firmware instructions are. Also, at the same time, the Lux readings from the color meters may also concur with the Nikon readings....lots to work with...thanks for sharing your thoughts on this....
Most of my stereo on 35mm / 120 film, is single shot, both shutters fire at once... I will provide some pix if you want to see these cameras.... I often to bracket.... the problem is, many scenes have moving subjects, and you have one chance to capture the image.... sure when everything in the scene is static, the options are limitless.... including your multi exposure, process, evaluate results, and adjust accordingly for subsequent exposures... an EXCELLENT strategy. Up to this point, I have not done my own processing, so this was too difficult to communicate with labs, so I just bought a few Jobo 2500's and will begin processing in house soon. Then I can experiment with what you suggest as I have control of the entire process.
The LF stereo has been dual capture on a slide bar (limited subject matter), but I will correct that soon by building stereo LF cameras. Just not enough hours in the day right now...
Robert Fisher
11-Jul-2009, 12:05
Mr. MURAMATSU (Nikon engineer) said:
"Basically, there is no need for us to change the film camera metering method for use with digital cameras. But we must remember that the allowable exposure range is smaller for digital cameras than for film cameras. At an early stage, we decided to adjust the algorithm out of concern about this difference. So, we inherited the “1,005-pixel RGB sensor” and refined its algorithm to achieve the latest “3D-Color Matrix Metering II” metering system. This new system, launched with the D2X, is now also available with the D50 and D200."
As stated earlier, I used an F5 for years shooting wildlife in every conceivable environment and was always shocked at my "kill" ratio shooting E6 film.
Is ANYBODY using an F5/F6 as a meter for LF E6 shooting?????
Ivan J. Eberle
11-Jul-2009, 16:05
I might be using either of my F5s more, if they didn't weigh as much as my medium format Pentax 645N, and if I didn't also have two DSLRs.
Now, I keep the F5s around for use as IR-triggered wildlife trail cams that are relatively expendable (in the instance that a dope grower stumbles upon one of my light traps).
Drew Wiley
11-Jul-2009, 16:51
Like I said, the meter itself is seldom the issue. Today I was so distracted by the
constantly changing light out in the redwoods that I got the filmholder in backwards and managed to double expose an 8x10 E-6. Can't blame the meter for that! And
I don't have any interest in carrying around a digital camera just to check readings, although it is perfectly apparent that that is where all the R&D money has landed.
Too bad they can't transfer some of that effort to a meter per se. But the Nikon technology you refer to isn't what I had in mind at all, though it is valid in its own
right. Makes no difference - nobody is going to develop a truly superior meter itself
because there's no money in it. Once you stick one of these inside a camera you
have all kinds of ulterior complications. I find a handheld meter superior even for
35mm photography. But to each his own.
Drew Wiley
11-Jul-2009, 18:11
I should follow up a little more just so you don't think I'm picking on someone. A
simple spotmeter fulfills a very important function. It allow YOU to place your values
right where you want them in relation to scene illumination. Every movie cameraman and a lot of Zone System photographers knows what this means. What an advanced Nikon camera contains is basically a tricolor meter with a lot of fancy probability software. It doesn't replicate the role of a spectrophotometer whatsoever. It tells you what the exposure should be based upon a lot of interpolation and stored
exposure information. What I was referring to is something which reads and mathematically calculates the linearity or curve of each sensitized layer, and then informs you of the actual placement of the values. I attempted to design something
like this for color darkroom printing and partially succeeded, but I have to plot the
values on graph paper the old-fashioned way. Of course, there's plenty of time to do
this, so the analogy to field photography is a ways off. But in the process I did
consult with some pretty high-tech electrical and optical engineers who hypothetically have the ability to design something more efficient. That's why I have an idea of what's going on and why this would be cost prohibitive for a conventional light meter. Nikon and Canon have taken a different path entirely.
Robert Fisher
11-Jul-2009, 18:24
Drew, thanks for all your input (Bill too). Effective next weekend, I will be using two meters - my Sekonic and a F5 that I purchased today.
810 E6 film is just too darn expensive to bracket plus the hassle of extra holders, space, etc. etc.
Don Dudenbostel
11-Jul-2009, 18:38
So that's half the equation. Does the effective speed of your film change at different color temperatures?
Unless your film is perfectly linear in color response then it will have slightly differing speeds at different color temps. Years ago B&W films were rated different under daylight vs tungsten due to low red sensitivity.
>What an advanced Nikon camera contains is basically a tricolor meter with a lot of fancy probability software. It doesn't replicate the role of a spectrophotometer whatsoever.
Drew, i applaud all your experiments and R&D... but I think you are over complicating this entire issue. Many people have reported just how finely well tuned the Nikon F5/6 performed with chrome film. That's the goal here, Nikon perfected it. If you put an equal effective fl lens on an F5/6, to achieve the same composure you have on your 810 gg, and you have full confidence in the F5/6 success with exposure with a given film, you just found a low cost proven solution to the issue being discussed here. In addition, the Nikon can be used in center metering mode, almost turning the meter into a spot meter. This is a brilliant approach IMO....
Robert I applaud your tenacity.... you are a Gettrrr done kind of guy. I can understand why you would not post your findings on this forum, but be sure to email me off list with what your findings, I am very interested. I am consumed by my day job till the end of summer so don't have a lot of time to experiment right now....
Don Dudenbostel
11-Jul-2009, 19:01
What I see as potentially useful information from your tests is that, if you photograph under varying color temps (e.g. indoor incandescent, outdoor daylight, etc.) then it would be a good idea to calibrate your process for each of those general scenarios.
The importance of this info ignores the other variables of photography. I agree with h p mktng Bob S that shutters are highly inacurate and vary with age and temperature. Ask don't assume there's no human error, film manufacturing tolerance and lab error. I've seen way too many errors of a major nature from kodaks film consistency and from lab errors. Overall these errors average out but not always. Certainly meters vary but every part of the process is subject to variables. My guess anyone expecting to achieve one shot perfection is going to be seriously disappointed.
Interesting to see the variables in meters but highly impractical to worry about in real world shooting.
> Interesting to see the variables in meters but highly impractical to worry about in real world shooting.
I would strongly disagree with this assertion. The thread covered many of the applications that critical exposure is very important. Its possible you did not read through the entire thread, which is often the case.
For many of us Don, it is extremely practical to prevent exposure reading errors that can be full stop or more. When I get paid to shoot a job, I need to produce properly exposed chromes. Because there is "other" potential errors in the down chain, is certainly no reason to dismiss one potential large error which exists in the first step of proper exposure. I never followed this logic. Specially if there is a simple method to avoid the error. It's possible with the type of photography you do, this issue is of no concern for you, so be it..... but I don't think its prudent to assert that everyone works as you do.
I have about 15 LF lenses, 8 35mm lenses and 12 MF lenses.... the worst shutter I own is off by 3%.... I test my shutters every few years, its remarkable how accurate modern shutters are.
Drew Wiley
11-Jul-2009, 19:50
I certainly don't always makes things this complicated! I developed a very specialized tool for modeling very precise interpositives, internegs, and color separations in color printing which has saved me a great deal of film and money.
Once protoypical models are in place for a certain category of work, the procedure
becomes vastly simplified. Similarly, the 8X10 chrome I accidentally ruined today
with a double exposure was made under diffuse fog almost like a softbox: any
averaging meter would have done an excellent job. But then the fog started lifting
and I was working with some extemely intricate shadow patterns which changed
every few seconds. I made both an FP4 zone-system style exposure and an E100G
chrome. I was visualizing the placement on each film curve very precisely, in
accordance with a finished print. I doubt an internal Nikon meter could have read
my mind, especially in such complex lighting! These devices are wonderful for the
photojournalist, sports, and wedding photographer, but I was working on the very
edge of tolerances for this kind of color fim exposure. I really like to dance with
the light, even though the odds are against me!
timparkin
12-Jul-2009, 09:08
Perfectly predicting the correct exposure value may never be 100% reliable-- but at something like $10/pop for a sheet of 8x10 color transparency film nowadays, it doesn't take a lot of wasted film to motivate one to improve upon a meter or metering regime if it can be improved.
Could somebody market it? Perhaps it's closer to hand than we think if we're stuck in some mindset of "tradition".
Killer app for an iTouch, iPhone (or my Blackberry Storm) for a LF photographer: a $9.99 download that matches the camera phone's spectral and DR response to various film types, and displays a histogram. (I'd pay more-- a lot more!)
I've had this in mind since I saw the first iphone - All it needs is a manual exposure mechanism and some calibration -
> Killer app for an iTouch, iPhone (or my Blackberry Storm) for a LF photographer: a $9.99 download that matches the camera phone's spectral and DR response to various film types, and displays a histogram. (I'd pay more-- a lot more!)
After reading the Nikon links above, a product like this would be very feasible.... but with the market shrinking every year, I doubt anyone would perfect such a product....
the revolution in electronics "allows" products like this to be a successful product,
but at the same time,
the revolution in electronics "prevents" products like this from being a successful product :-(
(i.e. the revolution caused the mass movement to digital capture)
Regardless, I think in the mid 90's, the meter companies missed an opportunity to benefit from Nikons successful metering technology, and offer something similar in a hand-held meter, mostly for chrome shooters. At that time, pro photogs shot chromes, not digital....
Robert Fisher
12-Jul-2009, 12:50
Bill great point about E6 in the 90's. I was using a pair of F5's for wildlife photography and NEVER would have considered negative film. In fact I don't know of ANY serious Nikon wildlife shooter using negative film at that period of time. I also wondered why Nikon never marketed a killer meter using their technolgy.
Kirk Keyes
12-Jul-2009, 16:46
If a meter is calibrated at one color temp, it should be relatively accurate at that color temp. Which I would suggest they are.
I beleive there is an ISO specification for meter calibration. It recommends that calibration should be made at 4800K. This gives the best balance between tungsten and daylight color temps.
But a manufacturer is free to calibrate at whatever temp they wish.
Ivan J. Eberle
12-Jul-2009, 17:24
The feasibility of an iPhone app actually seems great because it's not a new product with a manufacturing or tooling or R&D cost. It's just a software application for an existing product--one with a funky retro film hook.
Nikon should seriously do this. Call it "F5 and Be There", or something equally catchy.
BrianShaw
13-Jul-2009, 07:06
I beleive there is an ISO specification for meter calibration. It recommends that calibration should be made at 4800K. This gives the best balance between tungsten and daylight color temps.
But a manufacturer is free to calibrate at whatever temp they wish.
See page 5, post 45...
or
Page 84:
http://books.google.com/books?id=Q7uyzakcUrAC&lpg=PA84&ots=W4OnGtZWTi&dq=exposure%20meter%20calibration%20standard&pg=PA84
Leonard Evens
13-Jul-2009, 09:28
Someone has probably already said this, but let me chime in just in case. You should always test your exposure meter in connection with your actual experience using the equipment you have. There are so many variables---exposure meter, fil, lens settings, etc.---which can be off that it doesn't make sense to look at each separately. It is how they work together that matters.
Books on the Zone system go into detail about how to do this, but the basics are quite simple. Look at shadows and highlights to see if there is an overall shift in one direction or the other.
Peter De Smidt
14-Jul-2009, 16:53
I appreciate Bglick's sharing his results. The fact that meters vary is good info for photographers to have. Thanks!
>You should always test your exposure meter in connection with your actual experience using the equipment you have. There are so many variables---exposure meter, fil, lens settings, etc.---which can be off that it doesn't make sense to look at each separately. It is how they work together that matters.
Leonard, I can only assume you did not read through this thread before posting. While I do agree testing a meter with your film of choice is a good idea, its impossible to draw sensible conclusions of your tests if you are being fed inaccurate data from your meter. That was the purpose of this post. The message I brought forth has nothing to do with the other issues regarding exposure. It's not an "ALL or nothing" issue, instead, its trying to find the weak link in the chain.... and in this case, that weak link can vary based on the color temp of the light you are metering, or the color temp of the subject if you are spot metering... Considering how large the variances are, (further enforced by the book Brian linked to)..... IMO, if tight exposure is very important to a photog, than these issues are very relevant.
Brian, excellent find! here is some comments from the link you provided....
On Page 91
Most modern meteres use silicon cells which have a high sensiitivy to infra-red and a low sensitivity to blue, violet and ultra violet. This is, of course, the exact opposite of the sensitivity of film. SOME METERS CAN BE GRIEVOUSLY MISLED BY WARM LIGHT (LOW COLOR TEMP) OR BY RED SUBJECTS.
Another interesting point...
Matching a meters sensitivity to a given film - is allegedly done with the Zone VI modified Pentax meters to work with Tri-X.
Its also interesting that Pentax spot meters in their users manual give compensation values up to 1.33 stops based on the color you are spot reading.... further demonstrating how "off" silicon sensors are to color...
If anyone has the Pentax users manual that lists such, it would be nice if they post this info, it is very relevant to this thread. This is the first time I have seen a meter maker define how inaccurate meter readings at different wavelengths of light. Kudos to Pentax on this!!
What I also find interesting is.... the author does not test the meters under different lighting conditions and show his findings.... I would consider this mandatory as an author for a book on exposure meters.... he is clearly dancing around the finding I have presented, but did not go the extra mile and run some real world tests. Like most data in this field, what's available is often "half baked".
So far, I think Nikon is the only manufacturer has addressed this issue head-on. Their approach is brilliant.... isolate the colors in the scene, determine the intensity of each color, and provide exposure data based on how the film will react to these readings. This probably explains the amazing success Nikon shooters have with chrome films with the F5/6 (or possibly previous models).
Question on the Nikon F5/6.... does the film make different exposure decisions based on the type of film you have in the camera? Does the camera know if you have chrome or neg film in the camera? Color or B&W? I know the bar codes on 35mm canisters provide a lot of data, but not sure how much is read by the camera, other then the obvious ISO.
BrianShaw
19-Jul-2009, 11:00
What I also find interesting is.... the author does not test the meters under different lighting conditions and show his findings.... I would consider this mandatory as an author for a book on exposure meters.... he is clearly dancing around the finding I have presented, but did not go the extra mile and run some real world tests. Like most data in this field, what's available is often "half baked".
Many of us know Roger Hicks and even he would agree that he is more of a generalist than detail oriented or "scientific". He tends to rely on experience, of which he has lots, and his inate sense of summarizing these experiential findings.
It really would be nice to have a fully-baked treatise that is presented at a "normal photographer's" level of understanding (whatever that is since it seems to vary quite a bit) -- something that merges the science with real usefull application guidance. I hope that is where this thread ends up; it's not an easy thing to do I would imagine!
> something that merges the science with real usefull application guidance. I hope that is where this thread ends up; it's not an easy thing to do I would imagine!
Yes, this is always the goal..... I would suggest for now, the posting of that Pentax spot metering manual where it states the reading compensation for each color you spot meter is the best, and most simplified approach if one uses a spot meter. However, even this approach leaves out the actual color temp of the light striking the colored subject, but I am certain it is still better than trusting the spot readings with no adjustment factor. What makes the Nikon approach so brilliant is.... its sensor reads the color temp of light that is coming from the subject, which is a mix of the color temp of light striking the subject and the color of the subject itself. The Pentax compensation method assumes a fixed color temp of light striking the subject. This is why, it appears Nikon has created the ultimate color meter for color chrome films.....and the rave reviews through the years support this. Of course, I never even considered having this transpose to LF till others suggested this earlier in the thread.
I have ordered an F6 and a 24-85 zoom lens, and will be testing this in the future. The most simplified approach may come down to buying a Nikon camera, possibly some of the lower cost DSLR models and using it as light meter. (of course, it can do double duty as a DSLR) A 24-85 zoom matches the composure of .5 normal to 2x normal fl lens of LF. So if the Nikon gives near flawless exposures with 35mm chrome film with a given composure, it should offer the same for LF of the same film type and composure. This assumes you are shooting chromes, are critical about accurate exposure, and shoot in varying lighting conditions....
There is one issue with using a Nikon as a LF light meter.... which I will investigate. You have to be careful of the lens type you use. Lenses with MANY elements often consume more light than a more simple LF lens with typically under 6 elements. Some 35mm lenses have up to 20 elements... I have tested some of my 18 element 35mm lenses, and they consume up to a half a stop of light. Although modern coatings are superb today, they do NOT transmit 100% of light through each surface. Even at 99% transmission per coating, this is 2% loss for each air spaced element. 20 elements = 40 surfaces or 40% light loss. Not all surfaces are air spaced, which reduces the losses a bit. Within a 35mm camera system, this is accounted for, as the light reading is captured at the film plane, already taking into consideration the light transmission losses. Not true with LF, as we don't read the film plane (at least most of us don't, as there is such tools) This is quite easy to test, and the error is always consistent, therefore you can build an easy compensating variable into the Nikon ISO value. Hopefully the Nikon lens I selected will have light losses close to my LF lenses, and it won't be an issue. Just thought I would mention it, as its often overlooked. Older Vintage LF surely have worse transmission values per surface area than modern lenses. Not sure the cut off date, but I would suspect pre 1980 era...
Dan Fromm
19-Jul-2009, 12:25
"Even at 99% transmission per coating, this is 2% loss for each air spaced element. 20 elements = 40 surfaces or 40% light loss."
33%, Bill. If you're going to do the arithmetic, do it correctly. 0.99^40 = .669
If you're not going to do the arithmetic, then shoot for calibration. The lens' transmission is, after all, fixed.
Use a 50/1.8 Nikkor, not a zoom. Nice, simple, has as many air-glass interfaces as the typical LF lens. I can't imagine that you, with your passion for perfection, would buy a zoom.
Agreed with your math Dan, this was a simple explanation of transmission losses.... somehow we go from, this entire thread is absurd, and no on needs this level of accuracy...... then to expressing theoretical values down to several decimal places.... sheeeesh...
The point of the matter is, to find transmission losses of a lens, you simply measure the losses, no surface area math required. I get enough slack for too much technical mumbo jumbo, i was trying to keep it lite for discussion purposes...
As for your suggestion of a fixed prime lens for the Nikon.... You missed the point Dan......this has nothing to do with my passion for perfection. The Nikon camera is being used as a light meter, not to capture images. The goal is to match the composure on the Nikon, as seen on the ground glass, this would require a zoom lens, not a fixed fl lens. Re read above.... Make sense now?
I was thinking about this just yesterday, and a thought occurred to me: instead of a light meter, why not use a digital camera? Shouldn't a compact dSLR yield just as good results as a similarly sized and priced light meter, with the added benefit of getting an RGB histogram? Hell, a cheap-o pocket digital with a zoom lens might be just as good as a light meter for exposure metering.
There are of course limitations, mainly that the histogram of all cameras relies on the camera-generated JPEG, instead of RAW data (correct me if you know of an exception here). Whether this creates serious or even discernible deviations in exposure is questionable.
(I didn't read all the 9 pages, so perhaps this has been proposed before.)
The previous "2" pages addressed your concept ad nauseam.
I have come to the conclusion, no one reads a thread before posting :-)
Dan Fromm
19-Jul-2009, 15:01
"somehow we go from, this entire thread is absurd, and no on needs this level of accuracy"
Um, Bill, you're the one who insists on absurd levels of precision. Most of us get by being, by your standards, excessively sloppy. I'm glad that you've joined us.
Thanks for explaining why you bought a zoom. Does its range of angles of view cover those of the lenses you'll be using on 8x10?
Cheers,
Dan
> Um, Bill, you're the one who insists on absurd levels of precision.
Yeah, I hear Dan, I'm insane to correct potential 1.3 stop exposure errors when exposing dual 810 color chromes..... call me stupid.... thanks for setting me straight. I have gained a lot from you wisdom. (NOT)
> Most of us get by being, by your standards, excessively sloppy.
I addressed this at least 5x prior.... tired of repeating...please start reading....
> Thanks for explaining why you bought a zoom.
You mean for the 3rd time, right?
> Does its range of angles of view cover those of the lenses you'll be using on 8x10?
I addressed this too Dan.... arggggg....
.5 - 2x normal covers most of my captures on 810, 150mm to 600mm fl's....
Dan, you are always quick to always jump down someones throat. IMO, you can more effectively utilize that time by actually reading the thread, this gets old, real old.
As stated in my OP Dan, if you feel this level of precision, (+/- 1 stop) is more precision in exposure that you would ever require, then stop reading at that point, and move on to another thread. I stated this for a reason, so people like you don't start spear chuck'in, for no apparent reason....other than to waste bandwidth and make a thread so awkward, everyone gives up on it....if that is your motive, you succeed quite often at it.
Robert Fisher
19-Jul-2009, 18:14
Bill, if you are so inclined, please explain your "dual 810 color chromes" comment.
Thanks for all your input - it is always educational.
Dan Fromm
20-Jul-2009, 02:02
Bill,
Thanks for the clarification.
I appreciate your concern about getting the exposure wrong when shooting 8x10 chromes for clients. The costs of error, including loss of face and having to reshoot, are very high. Film and processing are the least of them.
I wasn't aware that you were selling stereo shots that started from 8x10 chromes. Please tell us more about that business. Not about your clients, but about how they use the 8x10 stereo pairs you sell them.
What is your failure rate? I ask because the two (2) meters I use didn't agree that well even when both were freshly calibrated yet both gave good exposures. I stick with the one that's a little easier to use.
I also ask because, although I blow more than my share of shots, the failures are much more often due to operator error -- that's me -- than to equipment failures of any kind, including light meter(s) that lie. Meters that give bad advice are the least of my problems. And I shoot mainly chromes.
Cheers,
Dan
Dan two meters that don't agree with each other when calibrated, is a recipe for bad exposure. Of course, you did not mention how far off they were, a critical issue....
My "TRUE" failure rate, i.e. when a chrome is not usable is very very low.... much less than .1%. But this is not about total failure, its about optimizing the exposure on chromes as often I have no chance for correction after the exposure. During mid day when color temps are near the 5k zone, my exposures are very accurate, within 1/3 a stop on avg. However, its when color temp changes, I notice chromes that can be off at times, maybe up to a stop at the most.... but I have had conditions where I was off 1.5 stops for a shoot.... and in all those cases, lighting was never normal. Extreme overcast, low light, high altitudes, etc.
I rely mostly on the Sekonic 608....its interesting how this meter faired in the test.... positive errors on the low side of 6k and neg. errors on the high side of 6k. Again, this information is based on the Gossen Lux readings, so I am not 100% certain this is is reliable as the Gossen has not been proven accurate as a light meter (yet).... after I get the Nikon I will learn more.... I will also shoot some film with the Nikon under many conditions and leave it in "auto" exposure mode, and see how well it tackles all kinds of lighting conditions. If I build the confidence level up others have with the camera, it will probably become my light meter. Too many times I think the light is 5 - 6k range, and a color meter tells me its 10k+.... our eyes are the worst color meters possible... and this is when the exposure errors often creep in...
Its very rare I have user error as I have learned the last thing I do before firing the shutter is read exposure, set lens, read meter again, fire....
Most stereo I shoot is not 810 chromes, as I need static subjects.... but even on MF stereo, I can blow through 20 rolls of 120 a day, it pays to perfect exposure.
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