View Full Version : Gossen vs. Sekonic meters - don't mix em
I recently bought a new Gossen Luna Pro S to back up my Sekonic 608. Big mistake.
I have been testing the two meters in incident mode, thinking both are "state of the art" meters, and both would be somewhat close in readings.
Rule #1 in photography - Assume NOTHING!
The readings were consistently off, with the Gossen reading .5 - 1.5 stops higher, at color temp ranging from 2500K to 9500K. I would have been happy with the readings having consistent differences, but this is surely NOT the case.
At first I thought one of the meters was defective. I assumed the Gossen since I had good exposures using the Sekonic for a few years. (but of course not as perfect as I would like) But, after speaking to Bogen (USA importer of Gossen meters) I made a new, but of course dissapointing discovery.....
There are no International standards on meter calibration, therefore variances are the norm. Gossen and most European photographic manufactures, calibrate their meters at 5600 degrees Kelvin, i.e. "Daylight" setting. Most Japanese manufacturers calibrate at 3400 degrees Kelvin, a "Tungsten" setting. This 2000 degree Kelvin difference in color temperature causes a difference in readings.
From my test results, the readings are very sensitive to color temp. It's my guess they are both accurate at the color temperture they were calibrated to. But outside that specific color temperture, it seems the readings are not as accurate. Does anyone have any have further insight into this?
Armed with this new information, it's not quite so easy to calibrate film to a given meter, as a single calibration test will only calibrate the meter / film when shooting under the same color temperture light which the calibration test was performed at. So, if you shoot under different lighting color temp lighting (such as in Landscape Photography), then ideally, you should calibrate meter / film under a range of color temp lighting.
To be fully prepared for field photoraphy, it seems you must know the corrections for the light meter under all color temps that can be expected. When in the field, you start with a color temp meter rerading, then take light meter reading. Adjust light meter reading according to a "cheat sheet" you carry. Does anyone have a better suggestion?
For MF and 4x5, I just bracket, but I plan to shoot a lot of 8x10, whereas brackets can get quite costly. Of course using Negative film vs. color chrome film will add some additional leeway for the calibration issue, but I much prefer the chrome film for scanning. TYIA
looks like it's time to get a third top-of-the-line meter. throw it into the bag with the other two and stand back!
Eric Leppanen
2-Dec-2005, 17:16
Color meter readings in the field is not an exact science, either......If bracketing is too expensive, I'd suggest QT Luong's technique of shooting two transparencies, develop one, and hold the second in reserve for push/pull based on how the first turns out.
I forgot to make one comment.... in a previous post about light meters and how they are influenced by IR light, a poster commented on a new chip that would make for the perfect light meter. The meter would decipher through programmed chips, what the color temperture is, and from there, provide the proper light readings. Also, he suggested the meter be programmed with many films, as it can be pre programed to films sensitivities at different color tempertures.
A few of us were ready to buy this "theoretical meter".... well, now, after this debacle, sign me up! I REALLY want to buy that meter!!!! I too wish, I had the expertise to design such, it would surely sell well, regardless of the price....
Kirk Keyes
2-Dec-2005, 17:34
"...in a previous post about light meters and how they are influenced by IR light, a poster commented on a new chip that would make for the perfect light meter."
Hey - that was me!
Anyway, in case anyone is interested, the chip is a Taos TCS230 color light to frequency sensor.
See http://www.taosinc.com/category.asp?cateid=11
I bought a bunch of Taos light to frequency sensors to try and make an economical microsensitometer http://www.taosinc.com/category.asp?cateid=20 which I have yet to do anything with...
Kirk
Eric, that still requires two shots...but regardless, its still a slight savings, but a logisticaly nightmare in my opinion. Specially considering I process film long after I shoot it. I tried this once, it became very difficult to hold all these pieces of film mark them accordingly, as I reload film holders constantly when on a photo trip.
I think if these variables can be nailed down tighter, the liklihood of missing an exposure is much less. Lots of leg work and testing to get there.
Also, when I used to "hold" one piece of film, it became such a mess trying to keep them all seperate, as I reload film holders constantly when on a photo trip.
I had sent back my Gossen MasterSix to Germany for repair. I was charged about US$150. But the meter could not give good reading. For example, I pointed the meter to a gray card under sunlight with ISO100 setting, it gave a reading of 125s and f22 or f32. Normally, it should be 125s and f16. I had talked to the factory but they insisted my meter had been repaired. Finally, I put this meter into my drawer and bought a Sekonic.
Kevin M Bourque
2-Dec-2005, 17:45
A man with a watch knows what time it is. A man with two watches is never sure.
windpointphoto
2-Dec-2005, 18:04
"A man with a watch knows what time it is. A man with two watches is never sure."
How true. One meter, one film, do a film test, never have to worry again. This is one of the reason there are so many film speeds for the same film.
Mark Carney
2-Dec-2005, 18:10
I sent 3 meters off to be calibrated once expecting to be a very happy person.
I now have 3 different exposures.
I was told that Sekonic and Gossen don't calibrate to the same mid gray standard. I never found out what Minolta used.
I don't use the Minolta anymore and adjusted the Sekonic to match the Gossen, as I had grown accustomed to working with it.
Mark
Mark,
I enquired about calibration of my Minolta Spotmeter F sometime ago and this is the response I received. It may be of some use to you but makes no mention of colour temp.
<--
The meter is designed on the assumption that the midpoint of the film
characteristic curve is receiving an exposure level of 0.1 lux.seconds.
The formula used to calculate exposure is :
2^EV= (B*S)/K where
B= luminance in cd/m2
S=ISO sensitivity of film
K=calibration constant (calculated to be 14)
-->
Fred, remember, unless you know what the meters reflective value was set for, as well as the the reflectivity of the gray card, then this test is unreliable. Even Grey cards that claim to be 18% can be way off....and it only takes maybe 4.5% off to equate to .5 stop.
And now that I learned that Gossen calibrates to daylight, as a landscape shooter, I would think these readings would be more reliable in the outdoors. But I refuse to make anymore common sense assumptions.
Kevin, a man with one watch doesn't know the time when it fails. :-)
Leonard... > One meter, one film, do a film test, never have to worry again. This is one of the reason there are so many film speeds for the same film.
I agree, but the purpose of the post was to explain how involved this calibration / test must become, as you must test at all different color temps. It certainly complicates matters.
On the subject of testing light meters, or better said, calibrating them. I once ran a test to check how linear the Seknoic 608 was. I placed the ambient dome behind a LF lens, and sealed up all the areas around the rear of the lens so the dome got all the light coming through the back of the lens. The lens was lit by bright room light from a white wall, no direct rays. I start reading with the lens full open, the continue to stop down one stop and continue to take readings. Assuming each higher f stop is delivering half the light, (as apertures are well designed for this task) then the meter should drop 1 EV per f stop. However, this test also did not go as planned, as the meter was NOT very linear. Linear referring to, one f stop equals 1 EV. At the high EV readings, 10+ EV, very linear. Hower at lower EV readings, < 10 EV, the readings were no longer linear. At some f stops, the meter would miss the f stop by .4 stops, and this became additive as I kept stopping down the lens..... not good....
However, now adding the color temp issue, it's a real pandoras box to get it right.... Kirk was really "ahead of the curve" with his proposed solution.... on the last post, I did not appreciate how eloquent his concept was! OH KIRK.... ARE YOU READY TO TEAM UP AND FIND SOMEONE TO BUILD THIS ULTIMATTE METER? On the last thread i was joking, now I am more serious!
Now, I wonder how I ever got good exposures :-)
tim atherton
2-Dec-2005, 20:29
"Even Grey cards that claim to be 18%"
and doesn't one of the standards for meter calibration involve 12.5 or 13% grey and not 18%?
ronald moravec
2-Dec-2005, 20:30
I don`t think selenium meters have this problem. My Weston Master with incident dome and Seconic Studio Delux match up well.
George at Quality Light Metric has had them both but not at the same time.
I`ll have to check out my Minolta Flash meter IV in ambient-incident mode if I can remember how it is supposed to work. The instruction book is obscenely long.
tim atherton
2-Dec-2005, 20:36
http://www.bythom.com/graycards.htm
http://www.kinesisgear.com/opinion.html#sekonic
Eric Leppanen
2-Dec-2005, 20:53
Bill,
I completely agree that the "two negatives technique" (shooting two duplicate transparencies, with the second being held in reserve for push/pull if necessary) is a pain on a long trip. It can be made semi-tolerable, though, by using one-gallon plastic baggies to segregate each pair of negatives. Since each two-sided film holder by definition holds two exposures of the same image, I can place a pile of exposed holders, a box of baggies, and my exposed film box in my changing tent; put each pair of negs in its own baggie; then store the baggies in the film box. When I get home, each baggie gets transferred to its own film box, and the boxes are dropped off at the E6 lab with instructions to normally process one negative and twin-tag it with its box. I can then separately process any of the duplicate negatives as needed.
This is certainly more hassle than simply dumping the exposed negs into the film box and being done with it. But it can be argued that having a duplicate neg is a good idea for a variety of reasons, especially when shooting 8x10 in the field (more susceptible to wind or other sources of vibration). Plus you might determine after looking at your first neg that better contrast or color separation can be achieved with a push or pull, even if the exposure of the first neg was technically accurate.
I understand, of course, that this system is not for everyone and may exceed one's threshold of pain! I use a similar technique when shooting B&W, as it provides much more control than separately placing exposed film in NOM, +1, -1, etc. film boxes.
Graeme Hird
2-Dec-2005, 21:47
Tim said ""Even Grey cards that claim to be 18%"
and doesn't one of the standards for meter calibration involve 12.5 or 13% grey and not 18%?"
The Gossen is calibrated to 18%, the Sekonic to 12.5%.
I use a Gossen Starlite. I'm a happy camper.
Tim, wonderful links.... once again, just demonstrates how impossible it is to get reliable information from anyone, even the manufacturers. The entire grey card concept is beyond me...
1. What is grey card reflective value? (sometimes this is not even stated, sometimes its stated wrong!) Kodak had a bunch that were not labeled properly years back.
2. What is reflectivity % is the meter calibrated for?
3. Angle of the grey card... almost impossible to get consistent readings.
4. Amount of ambient light sneaking in, altering the spot meter reading?
When this is all tallied up, it would be quite the project to get sensible results.... now add the other items that still apply from above.... color temp of light source, what color temp is meter calibrated to, how linear is the meter..... In my opinion, grey cards are pandoras box indeed....
R. Moravec. I beleive the meters we are discussing have Silicon photo diodes.... not Selenium... but you are correct, the Sekonic 398 Studio Delux does have a Selenium photo cell. Now, what are you suggesting this Selenium photo cell is not vulnerable to, which the Silicon cell is vulnerable to? Interesting, please elaborate....
Eric, I fully grasp your method, and I am quite impressed you can keep all this so organized. For me, changing film in the RV in side film tents, etc.... I could never get all this straight.....in addition, sometimes pushing or pulling more then one stop can cause undesireable effects of the film... but surely a workable solution for some. I would prefer to fine tune the exposure methodology and be confident it is close to "good" :-)
Interesting....just out of curiosity, I checked how Linear the Gossen Luna Pro S is..... I could only check it with low light levels. I used the same technique as described above. Results very poor, just like Sekonic 608. First reading at 5.8 EV. I stopped down the aperture 6 stops, so final reading should be down to 0 EV. But, it's at 2.4 EV. So 2.5 stops off. This is with a reliable relatively new Copal 0 shutter.
The color temp issue I can understand, as I think it's a case of "not enough meters sold", to justify the cost of re designing the meters with modern high tech methods, similar to Kirks reccomendations. But the linear aspect of the meter..... they have had 150 years to fine tune this aspect!
Graeme, most of this discussion is revolving around incident mode, so we have eliminated the % reflectivity issue.
Graeme Hird
2-Dec-2005, 22:09
Bill,
That's not just reflected calibration - that's the whole meter's calibration. Gossen uses 18% to calibrate reflected and makes the incident mode match it. Sekonic does the same, but with 12.5% as their calibration.
That gives about a 2/3 stop difference between the two, incident or reflected.
What I'm saying is that Gossen says 18% is middle grey, Sekonic say 12.5% is. Their meters will read light levels and calculate their results for that basic assumption.
tim atherton
2-Dec-2005, 22:14
then of course their is the story that Kodak decided on the 18% grey for their card because when they sent a Kodak engineer out to measure it into the Kodak car park in Rochester at noon in mid summer, the was the refelctivity of the tarmac...
Jeff Conrad
2-Dec-2005, 22:49
There actually is an international standard for calibrating meters--ISO
2720-1974, but I don't know to what extent manufacturers follow it. The
equation that Rob mentioned is the basic calibration equation used in that
standard. As far as I know, Minolta and Pentax use K=14, and Sekonic use
K=12.5 (a difference of a sixth of a step). The standard calls for
calibration at 4700 K, but few manufacturers seem follow this
recommendation. I think most use a CIE A illuminant (2854 K); in any
event, many authorized service centers use a Kyoritsu or similar tester
with a 2854 K light source. I'm not sure the calibration color temperature
is the main issue, for reasons I discuss later.
Calibration to a given reflectance is a myth. A reflected-light meter is
calibrated by aiming it at a surface of known luminance, usually
transilluminated; there is no reflectance involved. It's possible to speak
of reflectance when comparing incident- and reflected-light meters. If you
refer to ISO 2720 and do the math, a reflected-light with K=14 and an
incident-light meter with C=250 (flat sensor) should agree when reading an
18% reflectance.
In practice, this isn't always case; the difference may arise partially
from specular reflections from a test card, and there may be some issues
with calibration, especially with incident-light meters. If incident-light
meters are calibrated according to ISO 2720, and one believes
manufacturers' stated values for C (typically, 250 for flat receptors, and
330-340 for hemispherical receptors), the meters should give noticeably
different readings when aimed at a point source with the different
receptors. Informal tests that I've done comparing several Minolta and
Sekonic meters don't show nearly the difference that I would expect.
Inquiries to Minolta and Sekonic got nowhere; in fact, no one seemed to
have the slightest idea of what I was talking about. I've pretty much
resigned myself to accept the discrepancies between the behavior I expect
and the behavior I see as one of life's mysteries ...
A far greater issue than minor differences in nominal calibration is the
differing spectral responses of different manufacturers' meters. Some
years ago, I noticed incredible differences (something 3-4 steps) between
an (unmodified) Pentax V and a Minolta Flashmeter III under low-pressure
sodium light. I had the responses of the two meters measured. The
difference was considerable: the Minolta was fairly narrow, resembling that
of the 1932 CIE standard observer, while that of the Pentax was quite
broad, with considerable sensitivity to UV and IR.
Admittedly, nearly monochromatic sodium light isn't typical photographic
illumination, but I've found that even if the two meters agreed at one
color temperature, they may not agree under different conditions.
It's outrageous that a thread like this ever should be necessary. I've
always been frustrated by the lack of agreement among different meters; a
good luminance photometer, such as a Minolta LS-100 or LS-110, has a
response very close to that of the CIE standard observer. Admittedly,
these meters are quite expensive, and the CIE observer isn't quite the
response that one would prefer for film, but I don't see why it should be
that difficult to get reasonable agreement to a standard that roughly
corresponds to that of a typical film. This indeed was one of the
objectives of the Zone VI-modified Pentax meter. I've never had the
response of my Zone VI Pentax digital measured, but it seems fairly close
to that of my unmodified Pentax V except when reading through orange or red
filters.
I discuss meter calibration more extensively at
http://www.largeformatphotography.info/articles/conrad-meter-cal.pdf (http://www.largeformatphotography.info/articles/conrad-meter-cal.pdf)
Graeme.... I am not sure this is right. My understanding is, the incident dome diffuses the light source and the photo cell reads the intensity. That value is displayed.
Whereas with the spot meter, the light intensity is read by the photo cell, then it's displayed value is adjusted to account for the reflectivity value the meter maker programmed it for. Right?
Jeff, amazing pdf file.... you should be the one designing meters! I did not want this to consume my life :-)
Is my assumptions correct for making any meter calibrated to a specific film? Test at all light levels you will shoot in, at all color tempertures, evaluate processed film, make a cheat sheet for the field. In the field, use your color meter first, then the light meter, adjust light meter readings according to your chart.
This of course takes into account the non linear nature of the meters as I described above. I am not sure I will go through all this, but for starters, would you say I am on the right track?
TYIA
For me, there is no perfect exposure in a way, even if a meter would give it, or at least it sometimes seems difficult to imagine how this could be. How fortunate when one needs no adjustment for contrast control, local lab processing line and volume, or one's personal workflow - or has a light meter to get this all right.
I have a Minolta Spotmeter F, which was delivered quite a bit off from general reality. My Sekonic L358 arrived dialed in to what seems the most accurate of any meter I've tried. So, I calibrated the Spotmeter against it using a gray card, and they both agree perfectly now. Not very scientific, but it works. Since getting the inexpensive Sekonic, I shoot both sides less for exposure change but rather in case a shot I really like gets munched in processing, or to have a spare to play with alt. process while keeping the other pristine.
Anyone thought of making a light metering probe and/or dome for a palm type computer? It would be a real joy to have everything from reciprocity and film curve data through desired end processing parameters built-in to the meter. Seems like those little computers cost less than some light meters.
Jeff Conrad
3-Dec-2005, 00:28
Bill,
I'd never be able to bring myself to undertake even a fraction of what you
suggest. In theory, it might be a good start, but it would seem difficult
arrange the all of the desired color temperatures, and I'm still not sure
you'd have it covered, especially when reading objects of different
spectral reflectance. I can take readings of an object with either of my
Pentax meters (which usually agree within about 1/3 step), and have them
agree with a reading using a spot attachment for my Minolta Autometer IV-F,
and then go to a different object in the same lighting and have the Minolta
reading differ by 2/3 step ... I think it likely that at least one of the
readings is wrong.
I'd try to handle nonlinearity by having the meter calibrated periodically,
and noting any nonlinearities that could not be handled in the calibration.
You might need to ask the service facility to give you a calibration sheet,
but they usually only test 4 different levels, so recording actual vs.
indicated levels really isn't that difficult.
Handling the spectral sensitivity isn't quite so simple, and I don't know
if there's really a solution. Fortunately, both my main and backup meters
are from the same manufacturer, so they're usually reasonably close.
If I actually designed meters, I'm sure I'd see the big picture and
understand why it's impossible to have any two agree ;-). I'd also
probably realize that spectral response curves could be dangerous in the
hands of untrained riffraff ...
Emrehan Zeybekoglu
3-Dec-2005, 01:21
Interesting, enjoyable and informative thread... That said, and no offense meant, if I hadn't been taking photographs for a long time, or if I hadn't known anything about photography, reading this thread would certainly have discouraged me from starting it.. I'm not criticising anybody for discussing these issues; I'm just amused because what I've been taking for granted so far seems to bother some of us. There are so many variables in photography that, in my opinion, it's much better to forget about making it an exact science in the field and instead to concentrate on some optimal solution based on individual tests and common experience. Most of the time doesn't this give you the results you want? Is there any photographer who hits the target at 12 100% of the time?
Bill G - Don't want to sound like a smart aleck but wouldn't it be a simpler solution to carry a spare battery(or even 2) for backing up your Gossen? That's what I do..
Cheers..
george jiri loun
3-Dec-2005, 02:28
Actually Bill, your problem is easily solvable. Buy a second Sekonic meter and you'll be in the heaven you're looking for.
Michael Gudzinowicz
3-Dec-2005, 05:59
Bill,
Since you photographing in the field, there's a simple test to determine whether a meter is functioning properly. Set the meter EI indicator to 125, and in the reflected light mode meter clear blue northern skylight at noontime. The result should be the "sunny 16" rule... 1/125th at f/16 for EI 125. I've checked the result after calibrating meters using a Noritsu and it's accurate. If the meters don't give that reading, dial in a compensation factor for the EI. Just about all of your outdoor fill light is skylight, so temperature isn't much of a factor. To check linearity, do the same test using a stack of ND filters over the sensor. If either are off, consider recalibration. When using the incident mode, the Luna Pro should be aimed at the camera from the subject position... not at the light source which will give a higher than average reading. I don't use Sekonic.
Mike
A few basic points:
The 18% of a grey card is 2.5 stops less than 100%.
A K factor of 14 means 1 fourteenth which is 7.14% and a K factor of 12.5 is 8%. These are both a long way from 18%.
The best colour temperature meter you have available to you is FILM. It is designed precisely to distinguish different colours.
Reflected light will have a different colour temperature than the light falling on the subject. I.E. An incident meter capable of measuring colour temperature would be useless for metering reflected light subjects.
Every part of the subject which has a different colour would require a different meter reading if it were based on colour temperature. Funny thing is that film is pretty good at dealing with this.
Is middle grey 18% ? Only for a 5 stop range. For a 10 stop range zone V equates to 3% reflectance.
7.14% (Minolta K factor 14) equates to mid point of approx 7.5 stop range.
8% (Sekonic K Factor 12.5) equates to mid point of approx 7.5 stop range.
Kodak Instructions on Using a Grey Card:
“Position the grey card in front of and as close to the subject as possible. Aim the surface of the gray card toward a point one third of the compound angle between your camera and the main light. For example, if the main light is located 30 degrees to the side and 45 degrees up from the camera to subject axis, aim the card 10 degrees to the side and 15 degrees up.”
Own up who carries a sextant with them to measure the angles correctly. LOL
Why anyone would use a Kodak grey card for anything beats me although given what I have just said it occurs to me that it would provide a more consistent colour temperature across different lighting conditions. But you would need a reflected light meter for that!
tim atherton
3-Dec-2005, 07:50
"Set the meter EI indicator to
125, and in the reflected light mode meter clear blue northern skylight
at noontime. The result should be the "sunny 16" rule... 1/125th at f/16
for EI 125. "
hmm - that never worked for me in Tuktoyaktuk in January - or even in Yellowknife :-)
Keck > For me, there is no perfect exposure in a way... I agree there is other variables after the proper light level reading is had, but this does not discount the benefit of knowing the precise light level of the source.
Jeff, I concur with your comments, however, by staying with incident readings, we can remove the one big variable of the effects color temp light sources have when reflected off different colored subjects. Of course this is all part of exposure and we can't remove this variable in real world photography. However, at the time of exposure, if we can estimate the range of reflectivity % of the subjects in front of us, then we use some common sense to adjust exposure accordingly. Again, I certainly accept this will never be perfect. But this thread is starting to give me a better feel for some of the variables I can pin down. For one, just the lack of linear response of meters can easily cost us several stops, and with chrome film, this is almost a death sentence. I beleive the meter test, using the aperture as a means of reducing half the light is a very effective home brew test. Although small differences, say .1 stops per f stop can be disregarded, the additive effective of many stops, as my example above, should be a reliable indicator of how linear (or non linear) your meter is. It's my guess, from the 4 meters I have tested, NONE are linear.
Emrehan..... I realize this is sometimes daunting....and if one is very happy with their exposures using their meters and their techniques, then these threads should be overlooked. Overall, I have pretty good exposures also, but its far from a 100%, and if 810 film was not $20 per exposure, I would just bracket 5 shots per exposure and not even pursue the meter issue. Also carrying an extra battery for the Gossen has no relevance on what's being discussed. The fact the Gossen and Sekonic had such radical differences in readings is what caused me to re visit the subject of our meter's accuracy. Would a carpenter be happy missing measurements by 30%?
Michael..... Sunny 16 is not a reliable method to calibrate a meter, as their is too many variables such as, geographic locations, elevations, atmospheric conditions, color temp (blue skies).... these conditions create enough variables to be off 2 stops. I have tested sunny 16 for many years, and as a general rule, considering you can get close to a good exposure with no meter, it's quite a novel discovery and a good reality check, but certainly not reliable enough to be used as a meter calibration tool. Assuming it was correct, it would only calibrate the meter at one light level and at one color temperture, whereas this thread has discussed meters are not linear and react very differently to color temperture. So how reliable would the meter be at say 8 EV? I agree ND can be used to run the meter test, but trying to cover 12 stops with ND filters might introduce new problems, vs. closing down an aperture, which has been fine tuned for this task.
Rob.... > A K factor of 14 means 1 fourteenth which is 7.14% and a K factor of 12.5 is 8%. These are both a long way from 18%. WOW...this even further complicates the reflective exposure readings, thanks for sharing this. > Why anyone would use a Kodak grey card for anything beats me... I always felt this way, now that you introduced this K factor and how it relates to reflectivity %.... even more reason to avoid such.
I want to be careful not to toss the baby out with the bath water here. In one breath, I am ready to toss all my light meters and just use my eyes and guess :-) ..... but instead, I will take a more practical approach. The most obvious test to check my meters is the linear test. But this time, with a twist. I will test how linear the meters are at 3 color tempertures, the first at the color temp the meter is calibrated to, then one above, and one below. This will give me a clue how color temp effects the linear nature of the meter. If this test produces consistent results, meaning, the linear readings are "consistently off" with all 3 color temps, then I will proceed to thorough film tests. Then I will try to limit myself to that one film.
However, if the linear / color temp tests produce inconsistent results...... all bets are off, just too many variables to deal with. Then, I will shoot less scenes, and rely more on bracketing. The fact digital SLR's have histograms, will probably put an end to photographic light meter advancement. As a histogram and visual look of the scene solves all these problems. Which makes me wonder if calibrating a film to a digital SLR is even more reliable then then using meters. The histogram shows the recorded values and where they fall within the sensors recording range. If the sensor records similar to a specific film, well... this is a no brainer. Has anyone experimented with such?
A very interesting piece I found on Google search.....
Early photometers employed Selenium cells that exhibited an inherent, approximate match to the V(l) curve but these are rarely used today as they age quickly (their response drifts), they exhibit a large temperature dependence and the photopic matching is approximate at best and only suitable with incandescent lamps (broadband sources exhibiting a black body like spectral distribution).
Snip..... This is probably why the Silicon sensor has replaced most selenium sensors in "most" modern light meters. Of course Selenium still has the benefit of not needing a battery.
Bill G ->It's all relative. If one has a device that works at least in the same way each time it is used, then either that device can be calibrated or the other processes can be calibrated to it. Most light meters are more accurate than most of the shutters in my LF lens assortments.
Even in the "perfect" world of a digital camera, where the meter and sensitivity, etc. of the sensor are designed for each other, that meter leaves a lot to be desired. If one shoots neg film, either color or B&W, there's so much room for a little exposure variance provided there is at least enough exposure in the first place. Some of the finest photos in the world were taken with no meter, or even with a camera that had simply "snow/beach/bright, sunny, open shade and shade". 8x10 photography starts getting easier and better after just resigning to the fact that quite a few sheets will be wasted tuning into one's workflow for a while. Where it seemed insane
to waste fifteen bucks on a piece of film and processing instead of 8 bucks for a roll of MF with processing at one point, after a while it's okay as more photos come back looking nice. One
may shoot and process a lot of film in the time it takes to agonize over tech stuff, no?
How often does a nice day go by with no photos made, sitting at the computer or
fiddling with gizmos trying to figure out why they are so imperfect? Analysis paralysis
( one def: http://en.wikipedia.org/wiki/Analysis_paralysis ) is so much more costly
than a few sheets of film.
Interesting points you make though, and for my part - I hope that you get out with your
8x10 and make a bunch of absolutely gorgeous photos!
> It's all relative. If one has a device that works at least in the same way each time it is used, then either that device can be calibrated or the other processes can be calibrated to it. Most light meters are more accurate than most of the shutters in my LF lens assortments.
Not sure of your point here. I agree about your calibration comment, hence why i was only calibrating to film, or to the aperture for linear checking. As for your comment on the shutters in LF lenses? I can only comment on my new LF lenses all in Copal shutters. I checked 13 of them. All the shutter speeds were amazing accurate, the worst ones were at 92%, and even then, only a few of them, and usually at only one shutter speed, usually 1/500th. As for the apertures not blocking 1/2 the light on each f stop? Well if this is not happening, we have bigger problems then light meters. You may have confused my linear test? I was stopping the aperture down, not the shutter.
"Even in the "perfect" world of a digital camera, where the meter and sensitivity, etc. of the sensor are designed for each other, that meter leaves a lot to be desired. If one shoots neg film, either color or B&W, there's so much room for a little exposure variance provided there is at least enough exposure in the first place."
I agree, hence why I mentioned that you have to know the calibration between the digital SLR you are using and the film....just another way to skin a cat, its not a cure all for anything and everything.
" Some of the finest photos in the world were taken with no meter, or even with a camera that had simply "snow/beach/bright, sunny, open shade and shade".
This may be true....but what is the lesson learned here, we are better off with no meter at all? A meter that is not calibrated?
" 8x10 photography starts getting easier and better after just resigning to the fact that quite a few sheets will be wasted tuning into one's workflow for a while. One may shoot and process a lot of film in the time it takes to agonize over tech stuff, no?"
If it was possible, to just shoot film, and nothing else, I would do it. But if your improperly exposing shots, that you spent a ton of time, money, hiking, etc. to get....how do you reconcile for this? Do you say, next time, I need to open up two more stops? If so, why? Maybe the color temp of the light that day will not exist on your next visit....so your next visit, when the same meter is now reading accurate, you overexpose 2 stops by reacting to your last experience? Get my drift, one needs more information to work with, even if your relying on trial and error.
I don't mean to beat a dead horse, but I think its hard to deny that testing, and a good understanding of the test, with good equipment, can potentialy eliminate exposure errors in the field. My exposures quite often are dead-on, but sometimes, I use the exact same technique and I can be off by 2 stops....it's not common, but it happens...... other times, I can be off 1 stop.... so if I can get to the bottom of this once, and solve "most" of the field errors, my position is, why not? For others, they rather bracket, for some, the testing takes too much time and the results may be ambigous.... so why do it? Different strokes for different folks... I am willing to invest a day into this project, with the risk of knowing the results may not be helpful in the end. I respect those who feel differently. It's all a matter of how important the issue is to each of us.
Mark Woods
3-Dec-2005, 13:46
Hello Bill,
Here's a link to an article I wrote, "Candle Light to Daylight."
http://cameraguild.com/
Go to the tech tips section and click on the title of the article. My website is moving painfully slow or I'd send you there. It covers why a meter's reading changes with the color temperature. A graph is included and, hopefully, indicates the changes with my Minolta Spot Meter 3. Color Temperature is very important in relationship to reading a meter.
Kind Regards,
MW
Jeff Conrad
3-Dec-2005, 15:02
A K factor of 14 means 1 fourteenth which is 7.14% and a K factor of 12.5
is 8%. These are both a long way from 18%.
The K factor has nothing to do with reflectance; it's simply an arbitrary
constant in the equation
2^EV = N^2/t = LS/K
Where
EV = Exposure value N = f-number t = shutter time L =
Luminance S = ISO speed K = Calibration constant
A greater value of K calls for more exposure rather than less, as would be
the case if it referred to the reciprocal of reflectance.
In the article that I mentioned, I show a relationship to reflectance when
I compare it to the calibration of an incident-light meter; however, this
isn't necessarily magic, either--you could double the calibration constants
for each (e.g., K = 28 and C = 500) and still have the same nominal
"reflectance" relationship, but you'd obviously be calling for an exposure
increase of one step. You then would have the reflected-light and
incident-light meter agreeing on the same incorrect exposure ...
Jeff Conrad
3-Dec-2005, 15:30
For one, just the lack of linear response of meters can
easily cost us several stops
I don't think it should be nearly that bad--my meters typically have been
with +/- 1/2 step over all but the extremes of luminance.
As aggravating as it might seem, I think Marc's suggestion to get another
Sekonic for backup is the best solution. I agree with Keck that it's
somewhat relative, and at least if your meters are consistent, you should be
able to make them work without most of the testing that you suggested.
I completely agree with Tim about the perils of using the sky for
calibration--the luminance is sensitive to geographic latitude, and the
azimuth and altitude (angle above the horizon) of the part of the sky that
you measure. At moderate latitudes, it's good for a rough sanity check,
but not much more. If you want your meter calibrated, take or send it to a
qualified service facility--you'll save yourself a lot of time and grief
and film.
I guess I can understand Emrehan's comment that this thread might terrify a
relative newcomer. It's quite possible that we overstate the problem of
varying meter calibrations--it's more an annoyance that a major impediment
to taking photographs. Nonetheless, it seems an annoyance that we simply
should not have to suffer, and that may be the reason for some of the
passionate comments (including my own). There sometimes are good reasons
for using more than one meter (e.g., a handheld spotmeter and a 35 mm or MF
camera with a TTL meter), and it's aggravating when you get readings that
differ by 2/3 step. It's not that I can't learn to work around this, but
simply that I should not need to do so.
Kirk Keyes
3-Dec-2005, 17:06
I hope everyone reads Mark's article that he referred to a couple of posts ago. It is very interesting. It had a couple of bits that no one here has even come close to mentioning: "Mitch explained that the loss in green density is a byproduct of the yellow dye coupler as it reacts with the blue emulsion's lack of exposure and resulting loss in density." Another variable for color film users, and a very difficult one to even think about!
(Bill, remember how in the other thread you asked about cinematographers and what they do, I think we found one.)
I like the idea of using a PDA to handle the calculations from a homemade meter/color temp sensor. Check out this link (scroll down to light sensor): http://www.bonavolta.ch/hobby/en/photo/fotolab_hardware.htm
Claudio uses an interface box to get to a PC, but I'm sure the same can be done to a PDA.
Kirk
Mark, that article had some great information in it, thank you for sharing. Of course, it only confirms what I suspected.... the meters are not "always" seeing what film sees as color temp varies. Therefore, the only real form of calibration is with a meter, a film type, and varying light color temps and intensities. I am sure this will not cover all bases, as your article mentions very narrow wavelenghts that film can not see, which a meter does see.... but it should expose many of the corrections needed under certain conditions, including non linear nature of meters.
Jeff, have you tested your meters in the rear of a veiw camera and stopped down the aperture over a range and determined how linear they are? Although my meters all performed poorly, I once read this is actually very common, as modern Photo light meters are simply NOT linear, they all do well at a given light intensity. I am very curious of your results if you try it.
Getting a second Sekonic will not resolve these issues i am discussing. Although it's not a bad idea, to have two of the same meters for consistency. But, in any case, they can both be consistently in error for all the reasons discussed above, and the contribution by Mark.
Kirk, quite impressive gig....thanks for the link....
How sweet would it be, for one person to work all this out for each film, and sell the "smart" meter, then sell the chip set for each film tested.... this is how the rest of world works, i.e. R&D once, then everyone pays a small piece of the pie when they buy the product. But this is the photographic world, everyone must do their own R&D!
Jeff, I agree, that to a newcomer reading this thread, it would appear almost impossible to achieve a good exposure. But for many professionals, good is not good enough.... Ansel Adams was a great printer, but continually overcame obstacle by testing everything himself, not because he wanted an R&D firm, but rather, it was the only way to improve his printing. Even back then, Kodak and many large companies were around, yet it was him and a few co workers breaking new ground to advance the art. This being a forum with LF shooters, precise exposure is more of a concern to us vs. smaller format photographers. There is practical limits to how many film holders you can hold, backpack, how many times you will have that same scene in front you, etc. etc.....
Dan Fromm
3-Dec-2005, 18:41
Bill G wrote: "This being a forum with LF shooters, precise exposure is more of a concern to us vs. smaller format photographers. "
Um, Bill, I still have considerable KM135-36 in the deep freeze. I use it primarily for closeup work with flowers. KM is not forgiving of exposure errors. It is much, much less forgiving than b/w negative emulsions. I solve the problem by shooting it, for the most part, with a pre-calibrated flash rig. There's nothing special about LF as far as exposure goes.
Hi Dan.... well there is one big difference..... 810 is about $20 per exposure, vs. 35mm at about $.30 per exposure? So 35mm brackets are about $1 vs. $60 for for 810. In my world, that is a big difference..... and that was the difference I was referring to, as, each emulsion comes in every format.
Mark Woods
3-Dec-2005, 21:45
Thanks Kirk,
I know what you said isn't because I'm a Pasadena boy too. We should get together for a beer or coffee, your choice. (Tea too!)
A color temp meter solves a lot of problems if one thinks about the film as being a composit of 3 (or a multiple of 3 -- i.e., 2 Red, 2 Green, 2 Blue emulsions, or 3 of each. Usually this if for color neg and the different emulsions are high speed to get a base exposure, and the other emulstion are slower in speed and are designed to smooth the transitiions from bright to dark in that color). The color temp meter tells you the exposure each emulsion is being exposed to given the color of the light. This sounds abstract. All it really means is if you want it warm, shoot it warm, but you'll have big problems if you want to print is cool since there won't be enough information in the blue layer to give you a good image. Printed cool, the image will be grainy and have all the artifacts one would associate with a thin neg. BTW, this is for negs, not chromes. But the chromes will benefit from a Color Temp meter too if one wants to be consistent or replicate a look one shot before. Like an afternoon warm look, but it's the middle of the day in the shade of a hill or building. Match the color temp with filters. (I use the whole 81 series plus an 85 C and 85 B to achieve the results I desire. BTW, be careful with ND's since some brands will shift the color temp warmer about 300* K/ND .3).
Kind Regards,
MW
Mark Woods
3-Dec-2005, 21:59
Hey Bill,
Thank you for your kind words, but I'd like to mention that in my line of work, that use 35mm film, but shot at 24 fps, exposure is critical. And I can't bracket! With the cost of production rangeing from $3K - $10K/hour, I don't think the producer would tolerate bad or mis-exposed film. I do LF as a release from the stress of my work, and because I truely enjoy B&W. Besides I really enjoy this forum and what good would it be if I only lurked and didn't shoot B>)
Enjoy what you shoot, it's all good!
MW
Jeff Conrad
4-Dec-2005, 00:56
Jeff, have you tested your meters in the rear of a veiw camera and stopped
down the aperture over a range and determined how linear they are?
I tried something like this years ago with an MF camera, resting a Pentax
Spotmeter V against the film rails, with and without an interposed ground
glass. The results weren't very good, suggesting that something wasn't
linear. I took the meter and the camera and lens to a service center (as
luck would have it, the same person who took care of Ansel Adams's
equipment). He was skeptical of my test method (I forget the exact
reason); we checked both the meter and the lens with his Kyoritsu tester,
and both the meter and lens seemed fine (linear within 1/3 step or so).
Apparently the problem was my technique; in any event, I haven't tried it
since.
I probably should have mentioned that both of my meters (an
unmodified Pentax Spotmeter V and a Zone VI Pentax digital) have been off
by as much as a step when I've taken them in for calibration. The people
doing the cal usually have been able to adjust them to within +/- 1/3 step
or better at each of the calibrated light levels. I've resigned myself to
at least having each meter checked every 2–3 years; often they check
out fine, but sometimes they need adjustment. Which reminds me ... the
digital is overdue.
Witold Grabiec
4-Dec-2005, 10:53
Are we looking for a perfect meter here, that will give THE results we're ALWAYS looking for? I don't believe it's possible. It starts with film/developer manufacturing incosistencies, our metering techniques, repeatability of meter's aim at the target value (the real one within the scene) etc.
I suppose in a perfectly controlled space with lots of high tech gear it is possible to build a meter that will get close to exactness (someone) devised. But once placed in another enviornment, it is no longer exactly possible to repeat it's actual capability. To me the bottom line is maintaining the meter so it gives CONSISTENT output and test with your own procedure/materials (and occasionally recalibrate/restest as required).
Mark, I wasn't suggesting that 35mm shooters are immune to exposure issues, but my point was, with the smaller format end of photography moving to digital, which has the huge advantage of histograms, its mainly the very LF shooter who agonizes over wasted exposures. If I shot 16x20 film, I would agonize even more over these issues :-)
Jeff, thanks for sharing that story.... it makes me wonder...but the test, done correctly, seems near perfect, hence why I struggle with the test being faulty? But again, I assume NOTHING!
Witold, as I have mentioned above, I agree, the process of exposure can never be perfect, but eliminating shortcomings of a meter can only increase your chances of good exposure. I have never subscribed to the adage, "if you can't get it perfect, then forget it." I would be very happy with 95% success, if I started with only 85% success.
While I am in, obsessive Compuslive mode on meters. I took my 7 year old Sekonic Dual Spot F, which is a spot only meter, but it's perfectly designed for easy usage.... of course, Sekonic discontinued it shortly after the dual meters came out.
Anyway, I took the newer Sekonic 608 dual meter in spot meter mode, set both at 1 deg spot, and in 5500K degree light, from EV 6 to EV15, 80% of the readings were either identical or within .1 stops. The other 20% never differed more then .2 stops, or +/- .1 stop per meter. This demonstrates two meters, from the same maker, calibrated to the same source, are near identical in readings throughout their working range and differing life spans. (of course not always true, as failure can occur, variance in chips, etc) I am willing to bet, they would also read the same when exposed to varying color temp light. This is further evidence how accurate light meters can be, and from the Gossen / Sekonic tests, how error prone they can be when exposed to color temps in which the maker never exposed them to. Once again, it would be so much easier for the maker to test the meters once under different color tempertures and include a "corrections" chart with the meter.
george jiri loun
5-Dec-2005, 04:54
You got it , at last.
Marc, this was not the issue throughout this thread. My only point about the two meters is, there extreme accuracy to each other. But when using the Gossen and the Seknic and reading 2 stops apart, its obvious, they both can't be right. Therefore, this proved nothing, except, if you want two meteres caiibrated to the same source, buy the same make of each. But your comment makes it sound like, if two meters read the same, then the reading is accurate. It's obvious from this thread, this is a false assumption.
But even so, all meters from the same maker do not match so perfectly. Recently, I took a new Sekonic Twin Mate vs. the 608, it measured 1 - 2 stops different, I returned it. The two Sekonic spots, 608 & 778, where much more expensive meters, hence why they probably cross checked so well.
george jiri loun
5-Dec-2005, 09:42
Bill, get it right - if you want 2 meters be exactly the same in their measuring buy two identic meters. It's as simple as that.
Witold Grabiec
5-Dec-2005, 10:01
Bill, my only point (perhaps not made all that clear) was disconnection of lab environment in meter testing vs. real world use. Which ultimately led me to the conclusion that keeping the meter readings consistent is MORE important to good exposure than having it perfect on some unrealistic test target. In other words my meter may well be a stop off against yours, but right on for my total procedure.
Marc, last try, not sure if your not understanding what I was trying to accomplish, or just defending your earlier post.
I am NOT trying to get two meters to read identical. I am trying to have two meters that read accurate lighting levels under all color temperture light. Having two Sekonics alone, will not accomplish this task. They will give me two identical wrong readings under all color temp light except 3400K light. If one goes through all the trouble of doing the tests described above, you can easily make two different "corrections" charts, one for each meter, regardless if they are the same make. Although having two identical meters has other benefits, so I am not ruling that out, but its certainly not the solution to the issue which started this thread.
Witold, your point is well taken. In spot meter readings, your point is VERY valid, as it's not just the color temp of the light source, it also considers the color of the subject (target). The number variables are just too great to control, as a previous poster also mentioned. However, in incident mode, which only measures the light source, if I can deliver varying color temperture light to the meter during the testing phase, then use the same color temp meter in the field, I would think these should correlate well and produce more accurate light level readings. But until I test all this, I just don't know myself how error prone all this is.
In a different thread, I read about the processing E6, and a comment about adding 16% ? of time to the process when using Fuji film. This seems to suggest Fuji film processes to a different standard then other e6 films? I am curious how this can effect the outcome of processing. It's the first time I ever read of E6 films treated differently based on the maker? Any darkroom gurus care to comment?
Struan Gray
5-Dec-2005, 13:30
Bill, you need one of these:
http://www.oceanoptics.com/products/usb2000uvvis.asp
You'll have to also buy a short optical fiber and one of their cosine illuminance probes for sampling your ground glass. With this, and a handlheld PC, you can take a spectrum at each point on your ground glass.
Writing the lookup tables to determine the photographic exposure index for individual films is left as an exercise for the reader.
If you're feeling even lazier, and richer, there are devices called 'imaging spectrometers' which combine a line scan image with spectral resolution. Rotating the instrument, or taking successive datasets as your satellite moves relative to the ground, gives you an image with an associated optical spectrum at each pixel.
I've chosen to stick with one film and learn it's characteristics :-)
Struan, interesting devise, but surely a bit extreme for what I am trying to accomplish. I am simply trying to see how far off the light meter reading is under varying color temp light sources. I felt film was the best method of this, but involved, indeed.
For a simple cross check, I can put gels over a light source and then subtract the gel value of the pre gel light reading... make sense? Any other quick cross check ideas come to mind?
Struan Gray
5-Dec-2005, 14:05
My point was that if you don't want to make any assumptions about the colour temperature of your light or the spectral reflectivity of your object, there are tools that do the job, and at some point it's not worth fussing about with photographic equipment: you might as well go to the vendors who have solved exactly the problem you have posed.
I don't think quick and dirty tests of the meter have much validity, unless you have a very well-controlled light source. If you know you are dealing with fairly continuous-spectrum lights then correlating meter readings with a colour temperature meter could prove useful, but then you'll need to take the colour temperature meter with you (note: this is what most architectural photographers do). With line or narrow-spectrum emitters (and they're getting more and more common as incandescent lamps are made obselete) a bracketed test shot probably is the best practical and scientific solution.
I see a use for a calibrated digicam, with good temperature stability and the ability to read out the exposure values post-capture. Perhaps the next Picker will be selling modified Cybershots.
Struan, yes, I always have the color meter with me anyway....
What do you mean by a well controlled light source? What is the problem with putting gels over any light source and reading the temp of the light, then doin the cross check as I described? I was not aware that light sources, even incnadescent was not continuous spectrum?
Struan Gray
5-Dec-2005, 14:48
Incandescent bulbs are fairly good black-body radiators at their rated voltage and current. If you start, say, changing the current to get a lower or higher colour temperature, the brightness also changes so you're back to worrying about your meter's linearity before you can measure colour response. If you pulse-modulate the current, with a dimmer switch, you'll get a time-averaged mix of colour temperatures.
Basically, if you lack a good calibrated light meter of some sort, you end up trying to pull yourself up by your bootstraps.
Most of the households I've visited in recent years have a mix of incandescent, compact fluorescent, fluorescent and even LED lighting. All except the good old Edison light bulb have spikey spectra that can in principle cause gotchas with some films and not with others. A colour meter makes too many assumptions when converting the spikey spectrum to a simple colour temperature plus mired reading. My standard colour film is Portra NC, because I love what it does in daylight, but I sometimes get oddly saturated casts near unknown lighting fittings.
This is why optical workshops have an 'artificial sun', a model black body radiator that can be reliably tuned in both colour temperature and brightness. I only know of the optics research grade gear, which is pricey but has a calibration trail back to a National Standards body like the NIST in the US. I don't know how the equipment in a typical camera repair shop compares.
george jiri loun
5-Dec-2005, 14:59
Bill, you're speaking about photography "under all color temps" in the field etc. Experience is your best bet - after all, the temps are not so impredictable. You can learn with your MF format to know how the film reacts at for ex. the morning or the evening light. It's not a rocket science, fortunately. All the fiddle with corrections charts will just lead you away from the intuitive way you can learn from frequent shooting. I shoot commercially and I have to say that measuring the exposure is for me so automatic that sometimes I don't even pay attention to it at all. It's very rare I have the exposure wrong (and then mostly because the situation was impossible anyway - I shoot chromes). Just my humble opinion.
Struan... my testing method is much more simplfied......
Take single non fluorescent bulb that delivers 5500K light, set x distance from incident meter diffuser dome. Take light reading, put color gels in front of light source, take color temp reading, then light reading. In theory, the light meter should read the last reading, less the light loss of the gel (which the maker gives us). Then prepare a carrections sheet. This was the rough test I was referring to? What do you think?
Now do the same at different distances to vary the light intensity hitting the meter? Have a gel set up to maybe test 3200 4500 5500 6500 7500 9500 light. Then prepare a corrections sheet. Then based on this, I could always integreate a film test, but I was considering this first?
I could also set this test up in a box on a sunny day with no cloud cover... I can continously monitor the sunlight, but in the amount of time it would take to complete this test it shouldn't vary much? This light source would more easily duplicate real world situations, since I shoot with landscapes. Your thoughts?
Struan Gray
5-Dec-2005, 15:13
On my way to bed.....
How do you make 5500 K light into all those different colour temperatures in a way that is accurate to, say, 1/6 of a stop? Trust the gel manufacturer's filter factor? But then you have to know which spectral sensitivity they assumed when they came up with the filter factor.
I'm not trying to be argumentative. Just pointing out that you can very easily end up going round and round in circles. Either you accept that good enough is good enough (in which case there is a strong argument for test shots on film and a $1 notebook), or you invest in a precision instrument with a known and stable calibration.
Some measurements are inherently stable with time. A good mechanical balance will still be a good mechanical balance after ten years in a cupboard. Sadly, even the best optical sensors need regular calibration: for lab instruments there is a whole industry dedicated to periodic recalibration, with an audit trail back to rigorous standards.
Struan, I follow your reasoning.... I probably had too much confidence in the gel makers filter factors for this test to be successful. It seems you feel this is not reliable, and it makes sense.
Even more discouragement.... Today, Mamiya USA advised me Sekonics are calibrated to 5500K light source. Now, there is no excuse of the Gossen Luna Pro S to be this far off when put under different color temp light. Now it's really clear just how different meters react under different color temp light. Gossen and Sekonic are way apart.
Marc, I shoot chromes too, and I do a good job with exposure, but there are certain times, when things go astray. If I shot MF, or 4x5, I would just bracket to be safe, but with a big 810 project I was considering, this much bracketing can be very costly and physically difficult to manage. Good reason to shoot 5x7 :-), right QT?
Mark Woods
5-Dec-2005, 19:22
When using filters to change the color temp, read the results with your color temperature meter. Read the compensation with your incident meter. Make your exposure, or braket it, and see what the results are. This will calibrate your meters with the color with the resulting density. I do this for my work and it works. (Lately I've been reading the difference in density of the bracket with a densitometer to make sure I have consistency and note it as a change in EI.)
MW
Jeff Conrad
5-Dec-2005, 20:11
I'd still consider getting another Sekonic if you need a backup. It's not
going to address the issue of spectral sensitivity, but at least it should
eliminate one headache. I'm not sure that the calibration color
temperature is a major issue (see below); as several of us have suggested,
the different spectral reflectances of different objects (which, of course,
combine with the effects of the color temperature of the illuminant) could
be far more significant.
I suspect that the filter packs used in luminance photometers such as the
Minolta LS-100 and LS-110 are a bit pricey for use in photographic meters,
but I don't see why it should be so difficult to use a less precise filter
pack that reasonably approximates a “typical” film. I say
this, of course, as one who writes about meters rather than designs them
... Given the variation in spectral response among films, it isn't
practical to get a perfect match, but there would seem no excuse for the
wide manufacturer-to-manufacturer variations that some of us have observed.
Picker recognized the problem more than 20 years ago, but the economic
realities of a small company probably made the result less ambitious than
the original objective. It's sad that the meter manufacturers haven't
chosen to address the issue. Mark's experience is quite revealing; if
cinematographers don't have the clout to demand a color-corrected meter, it
doesn't look good for the rest of us.
ANSI PH3.49-1971 called for the meter's response at 2854 K to be within +/-
1/4 step of the response at 4700 K. How closely manufacturers complied
with this, I don't know. PH3.49 finally was withdrawn several years ago in
favor of ISO 2720-1974; the ISO standard calls for the spectral behavior to
be “assessed,” but seems to include no requirement for
reporting what was assessed. ISO 2720-1974 also requires that
“The spectral sensitivity of the meter shall be continuous over the
wavelength range 400 to 700 nm but shall not extend appreciably beyond this
range.”
Hardly the most rigorous requirement, and again, no requirement for
reporting. Pentax brochures of 20 years ago included curves indicating
about 50% response at just below 400 nm, and close to nil at 700 nm. The
test that I had run suggested that the response extended considerably
beyond 700 nm, but I didn't actually observe the test and can't speak to
the traceability of the measuring instrument. I don't think I've ever seen
a published curve from any other manufacturer.
I'm with Struan with respect to improvised tests—over the years, I've
tried more half-assed procedures for all sorts of things than I care to
admit (one of these days I'm gonna learn ...). They've worked in a few
cases, but most of the time, they've resulted in nothing but frustration
and wasted time and effort. If you want to ensure the linearity of a
meter, send it to a facility with a proper tester (such as a Kyoritsu)
who's light source is within the calibration period. If you're really
curious, try to find someone who can run a spectral response curve (and let
the rest of us know what you find!).
Mark, perfect, finally a supporter :-) I am curious, from the work you have done, how much compensation did you find that needed to be applied? What films? I am curious how extreme the corrections needed to be?
Jeff, wonderful post, I am fully with you, and probably will get a second sekonic for the reasons you mention. If for no other reason, the Sekonics are more versatile. I too have run tests that end up a waste of time and money....but sometimes, they have been very useful. You have to pick and choose carefuly, hence this thread :-)
Are you suggesting there is a firm I can send my meters to, which can do the actual test I am referring to, which includes different color temperture light? What company would run this spectrual response curve? But even with this, I need to see how it relates to the film. But it sure would get me closer to being accurate, even with NO film tests, right?
I am interested! And I would surely share the results!
Jeff Conrad
5-Dec-2005, 22:31
I'd probably start with a spectral response curve, which should tell you
much of what you need to know. I doubt that it will answer all your
questions, especially the required corrections, but I suspect that having
someone else generate all the answers could be an expensive proposition ...
Response curves for most films are readily available, and you at least
could compare the meter and film curves and see where you had major
differences. Who knows? You might even find that the mismatch isn't as
bad as you fear.
I had my tests done over 20 years ago in the SF Bay Area, and I don't even
remember the name of the person who did them, so I can't, offhand,
recommend a firm. I do recall that I had to make several phone calls, and
had a hard enough time even finding someone who understood what I was
talking about ... What you're envisioning goes somewhat beyond what I had
done. You could start with a Google search for “spectral
response” testing. You also could contact people like Minolta or
X-Rite, who make spectrophotometers; they might not be able to do the
tests, but might be able to suggest someone who could. You also might try
C.R.I.S.S Camera Services (www.criscam.com), who do all sorts of meter
calibrations. I'm not sure they could run a curve; however, they also
distribute Kyoritsu, so they might be able to recommend a facility with
suitable equipment for testing response at different color temperatures.
You might need to use two different facilities. Folks who can measure
spectral response tend not to deal with photographic exposure meters or
luminance photometers, and folks who can test photometric response tend not
be able to measure spectral response. Essential in either case, I would
think, is to ensure that the test equipment is NIST traceable.
The most accurate approach to testing the effect of color temperature
probably would be to have the test done with an unfiltered calibrated light
source, such as the Kyoritsu LBF series (not the multi-function testers)
that can be had with CIE A or B illuminants (2856 K and 4874 K). Other
color temperatures probably would require color conversion filters, and you
would need to ensure that you could trust their characteristics (it would
be interesting to see what Sekonic use for their 5500 K calibration). To
be honest, the service facilities that I've used have had only the
multifunction testers rather than these specialized light sources, but I
haven't really looked for a a place with a specialized light source,
either. You might learn quite a bit just from 2856 and 4874 (or any two
color temperatures reasonably far apart)—if the meter responses
weren't too far apart, the color temperature of the light source might not
be such a big issue. The matter of spectral reflectance of different
objects would remain, of course.
Kirk Keyes
6-Dec-2005, 10:54
"If you're really curious, try to find someone who can run a spectral response curve "
I've done a bit of playing around since my last post, and I believe that I can to this. Run a spectral response curve for a light meter.
I've got an old Beckman Spectronic 21 spectrophotometer that has an optical port on the side for a sample holder larger than the regular test tubes or 1-cm cuvettes that it is designed to take. Since the Spec 21 was having issues and I had bought a monster scanning spectrophotometer (a Spectronic 1201, and if anyone has a manual for one of these, please let me know), I figured I could poke around a bit in the Spec 21.
So I first placed a white paper into the light beam of the Spec 21, and tried to meter off that, but it was too dark. I didn't have any mirrors small enough to place in the path to bounce the light up through the cell holder, so I got out the screw driver and removed the additional cell bay and now I can aim the light meter directly into the light beam. And in a darkened room, my Minolta Spotmeter F gives an EV reading of about 5.5 or so with the wavelength of the spectrophotometer set to 550 nm (nice green color).
By changing the wavelength that the spectrophotometer is set to, I can generate light that goes from 1000 nm down to 340 nm. That's a more than wide enough range to determine not only response to different colors, but also any influence from near UV and farily good into the IR. The light from the Spec 21 has a bandwith of 20 nm, centered on the value indicated by the wavelength selection dial, so it's not really narrow bands of color that I can test the response for, but it is certainly close enough for this kind of application. (Perhaps I can adapt the Spectronic 1201 if this is needed someday as it has a 2.0 nm bandwidth, but that also means the less light going through the spectrophotometer.)
So I spend a couple of minutes with the Minolta Spotmeter F, holding it so I could get the light into the spot area and then twisting the wavelength selector and seeing the reading of the meter change as the colors generated went by. Kind of cool - I could even see an image of the light bulb filament which makes sense since there are no lenses inbetween the meter and the spectrophotometer's light bulb, it's all front surface optics so I was looking onto a couple mirrors and then seeing the filament.
A few issues that I can already see -
1) Getting the meter aligned to take a reading through the end of the spectrophotometer is going to take some time. A tripod will definitely help with that. Not sure how repeatable that will be. The target area is about 2 x 5 mm in size.
2) The light from the spectrophotometer is not very bright, as I said, EV about 5.5 for the Spot F. That will give about 5 stops of readings that can be made and that should be enough to make a graph of the spectral response with. (The spectrophotometer has a "beam chopper" to split the signal so the spectrophotometer can comare the light that goes through the sample with the intensity of light that does not. The chopper is simply a fan blade that goes between the light bulb and the entrace for the slit before the diffraction grating. I think I can disconnect the motor without problems, it cools the lamp, but I can run the thing with the cover off to help with cooling.) A brighter bulb may be possible with some more diassembly of the spectrophotometer...
3) The instrument switches the order of the diffraction grating somewhere around 500 nm. That means the intensity of the light will be offset from one side of the scan to the other side. This will make a discontinuity in the generated graphs, but all data from either side will be comparable. Perhaps the offset can be reduced in the graphs by comparing data from each side of the switchover wavelength.
4) I don't know what electronic control the spectrophotometer circutry has to maintain the bulb voltage. I guess I can hook a volt meter up to it to see, or take readings with an incident meter to see if it is stable enough. I could run it though at UPS to help filter the line voltage. The bulb runs at 12 volts (looks like a brake light bulb, but they cost a lot to replace as they are soldered to a PC board to make sure the filament is in the right position.)
5) I was thinking of taking an old quartz cuvette and frosting it a bit to even out the light to make a more uniform target to aim the spotmeter onto. But then it will cut done on the light intensity.
6) The color temp of the spectrophotometer light bulb is probably around 2800K. (I'll rent a color meter and check this if this method pans out.) So that means the light going into the spectrophotometer is very warm, and not a match for a daylight source. But if we want to play with some math, I think we can take the spectral data from a 2800K light souorce and generate a response curve for 5500K, or any other temp if we have the spectral curve for that temp.
7) Since I have no way to calibrate this kind of device, all the measurements would be on a relative basis. But that should be enough to tell us about the spectral properties of our meters.
I've only played with the Spotmeter F at this point. I also have a Flashmeter IV incident, a Flashmeter VI spot/incident meter, and a Pentax Spotmeter V. (You may have seen they thread about disassembling the Spot V so I can replace the light in it - that was so I could make readings of the spectrophotometer but I can see the scale in dark conditions with no light inside the spotmeter.)
I think I can make pretty reasonable readings from meters with tripod mounts, and I think I can rig up an adjustable mount for ones that don'thave a tripod mount, like my Flashmeter VI. And I also think I can do readings with the incident meters - I don't konw about other incident meters, but with my Minolta ones, I can take the incident domes off and run them without the dome. That will allow me to shine the light from the spectrophotometer directly onto the incident meter cell. The Minolta Flash VI will read about EV 0.0 with full moonlight and no incident dome on it.
I'll play around some more in the next few days, but if I can get some volunteers that are interested in getting a spectral sensitivity scan of their light meters, I'd be willing to give it a try.
Any volunteers?
Kirk
Kirk, I am glad to see you so inspired! It's possible your testing, will shed some light on this subject, even within the narrow band of EV you are working in. Based on Marks tesing and my experience, I am confident some clear issues will unfold.
I realize your test is a "rough test" but at this point, that is one heck of a start. If you discover variances of significant values, of course, it would make sense to further pursue this on a more rigorous / controlled test, covering the full EV range of the meter and getting a better grasp of the variables. I am curious of the input of the other thread members on your test. My meter can read as high as 16 and as low as 2 EV, both being just as important to me. If your results show no major variances, then, we will be left wondering, was it the low EV, was it the wavelenghts of light you used, etc. A color meter would surely help.
Then, even when finished, this needs to be measured against film, the ultimate subject to be calibrated to, but considering variances in batches of film and processing, I would be just as happy having an accurate light meter reading under given color temp light. My position still stands, having a meter that reads accurately (relative term indeed) under all color temp light gives us a better exposure calculation vs. a meter which is NOT calibrated to such.... I realize it does NOT eliminate the other variables raised in this thread, but its one less error prone area, i.e. assuming we get some clue just how far off this can be.
I know from years of experience shooting outdoors, my meters can occasionaly be quirky...but in my photographic mindset of "assume nothing" I am not 100% sure its color temp causing it, but I have no other sensible explanations. My recent Gossen vs. Sekonic test clearly demonstrated the huge variances in the readings, and I can't imagine how the same EV light level readings can differ .5 stop one day, then 1.5 stops another day, both at the same EV range....the only variable I "KNOW" is changing is the color temp. Of course, it's possible there is other explantions for this, as both meters use a different photo sensor.
Keep us posted! Thanks Kirk!
Jeff Conrad
6-Dec-2005, 17:41
I think the 20 nm resolution should be more than adequate to address the
questions posed here.
I'm especially interested in seeing how the Spot V compares with the
Minolta meters.
Bill,
My position still stands, having a meter that reads accurately (relative
term indeed) under all color temp light gives us a better exposure
calculation vs. a meter which is NOT calibrated to such.... I realize it
does NOT eliminate the other variables raised in this thread, but its one
less error prone area ...
I couldn't agree more.
At this point, I'd settle for knowing what the meter actually does,
regardless (well, almost) of what that may be. I should add that it's
outrageous that photographers should need to undertake a test like this
themselves.
Maybe some of the advanced techies here can explain.... when a color temperture meter reads a value, say 7500K. This value is based on R, G, B values read by the individual color sensing device, right? In Photoshop, a given RGB value, can only be one color, such as 128,128,128 is middle grey.
But in a color meter, can a 7500K reading come from differing RGB values, or only ONE set of specific R, G, & B values?
This may have been answered in some of the above posts, but it was not so clear to me.
Jeff, I am so glad you keep voicing your position on just how crazy it is that professional lightmeter makes do NOT offer this information with their meters????
It leaves users with the daunting task which are out of our league, as a light meter is just a tool for us. Oh well, to me, it's just par for the course in every aspect of photography I have experienced, from photo gear, scanning, film... only the printing end is a bit more sophisticated as one camera can produce thousands of prints, so as expected, money dictates service. I can't imagine a product being more mature then a light meter, over a 100 years, and we are still doing the same thing with the meter, yet still issues like this are a mystery. I mean how much would it cost of Sekonic or Gossen or minolta to include this information? Anyway, I just wanted to support your rant, as you have been carrying the load on this one! :-)
I too would be happy knowing how the meter is reacting, that would dictate just how much time and energy I would be willing to put into the film testing phase.....
Mark Woods
6-Dec-2005, 18:38
I generate my characteristic curves in Excel. These are based on RGB density readings with a densiometer at the lab I run my film through. I use my color temperature meter to set the light to 3200*K (since that's the film I work with), and expose the neg in 1 stop incrments. I track the density in RGB (3 different lines on the graph) and make a determination about what it all means. I like this system since it's my meters, I know the lenses I'm going to use, it's using the lab that's going to process the film, and I'm the one reading the meters (spot reading off a gray card). So it all fits together for me: meter reading with the actual meters, meter application (how the stop is read), film handeling, and processing. I don't think the meter manufacturers could give this information out since very few people meter light the same way, besides they'd be in a lab some place and not out in the field. ;-)
Hope this helps,
MW
Mark Woods
6-Dec-2005, 23:41
Hey Bill,
As a lawyer friend of mine says, "There are many ways to skin a cat, and they're all ugly!" There are many ways to achieve the color temperature you desire with RGB and YCM filters. I have diminished the green layer with a magenta filter only to have to use a cyan filter to cut down the red cross talk with the magenta light/filter. It worked and the final product was really amazing. That said, again, there are a number of ways to change the color temperature that will affect the film differently. I personally have a set of YCM filters that I use on a regular basis. If I could justify it, I would buy a set of RGB filters and could make any combination of CT shift specific to a color layer. Man, that would be the bomb! I just ran out of money and jobs before I got there and don't know if I'll be there again with all the shift in technology.
MW
Mark, thank you for the nice response...... for the benefit of many of us who are not quite as educated and experienced as you, tell me if this is correct....
A given color temp can be the result of many different RGB values. For example,
xyz values for RGB = 7500K, and
abc values for RGB = 7500K
If this is correct, then using a field color temp meter in my proposed solution in my early post...... the color temp value is NOT enough information to apply an accurate light meter correction factor.
For my proposed system to work, we would need the individual RGB values the color meter is reading, not the combined color temp. Then we could apply an accurate correction factor to the light meter reading. This assumes there was a set of curves done in a lab whereas it produced reliable spectral response curves at many different light intensity levels. I certainly understand none of this is feasible, but just making sure I am grasping theory of what would be necessary.
Yeah?
Mark Woods
7-Dec-2005, 15:02
Bill you got it right! There are spectometers that can analyze color in terms of RGB. I believe Spectra meters used to sell a meter that did that. It was one of the original color temperature meters. The current meters are designed for Chromes and Color Negative film for motion picture work. The old Technicolor field technicians used meters like the older Spectra meter. They had filters made up for the common exterior lighting one would encounter on a MP film. That said, they knew the bias of their system and could use magenta to shift the daylight color temperature instead of red when in a very green environment (magenta is the complimentary color of green and can diminish it's effect on the image, like having a green reflection from plants). It's a lot to wrap you mind around, I find it interesting, but I know I'm a minority. If you're dealing in a 5500*K (daylight) environment, I don't think your meter, nor you CT meter, will be off because of the color. In a 3200*K environment, Kodak reccomends decreasing the EI by 1/3 stop (i.e., open the stop up by 1/3 stop). When I was shooting B&W on Tungsten lighted sets, I did that and had no problems. I don't compensate the meter for color neg balanced for Tungsten.
Hope this helps.
MW
Thanks Mark, I thought I had it right, I just needed you to slam dunk it into my brain :-) This further demonstrates just how tremendously difficult the variables are to fine tune exposure with color temp. This also further solidifies just how brillaint Kirk Keyes "Ultimate Light Meter" concept is. The most painful part being, his meter concept is easily attainable with todays technlogies. Starting with proper indivudual R, G, B values and having a meter calibrated then programmed to correct for each films response would surely be "Light Meter Utopia". And with so few films left, this is not such a huge task. Test once, share with everyone, what a novel concept, anyway, Kudos to Kirk Keyes!
But back to the real world..... Mark, is there any general rules that are sensible, such as, if a meter is calibrated to 5500K light, then at 3200K decrease exposure 1/3, and at 8500K, increase exposure a 1/3 stop? I am just tossing these correction factors out since you used 1/3 in your example. If in the end, this is the extent of the corrections we need, well, the problem is much less then I feared. (which would be the only good news so far) Any general rules of thumb that exist such as this? Can we at least say, under 5500K decrease exposure, over 5500K increase exposure? Or is this assumption also dangerous?
Kirk Keyes
7-Dec-2005, 17:10
"A given color temp can be the result of many different RGB values."
And it is dependant on the color space that you are generating the RGB values. (Unless you are talking about RGB densities here.)
I've made a graph of the Minolta Spotmeter V's spectral response. I just need to upload it so I can make a link to it for you guys.
Kirk
Mark Woods
7-Dec-2005, 18:31
Hi Kirk,
I was speaking of RGB densities, not color space which is a whole other ball o'color. ;-)
MW
Jeff Conrad
7-Dec-2005, 19:17
It's possible to get the same 3-point response (e.g., RGB) from many
different spectral response curves—this is why you get metamerism.
It's also why you get more a more accurate profile of a monitor or printer
with a spectrophotometer than with a 3-point colorimeter.
I think most incandescent light sources reasonably approximate black body
radiators, so the concept of color temperature is applicable. The
spectral response curves of film and blue-filtered silicon photocells are
nothing like those of a blackbody, however. It's probably reasonable to
recommend speed adjustments for a given film at different color
temperatures (Kodak have had considerable experience ...). It may not be
quite so simple to apply corrections for changes in meter response,
especially if meter response curves differ among manufacturers. If we
believe the old ANSI standard, the response isn't supposed to change that
much with color temperature, although I certainly wouldn't assume this
without some good test data.
Again, I think changes in color temperature may be the lesser problem
compared with a meter response curve that bears no resemblance to that of a
blackbody or any film, and which is influenced by the spectral reflectance
of the object metered as well as the characteristics of the illuminant.
I've seen two meters agree on a gray card yet differ by three steps when
pointed at ostensibly blue or red objects. I say ostensibly, because the
objects may have differing reflectances outside the visible spectrum.
The problem is well illustrated by this graph (http://www.davidromano.com/trixfilm.jpg) on David
Romano's site (http://www.davidromano.com/). This is exactly
the behavior described by Fred Picker when Zone VI released the modified
meters: relative to film (Tri-X was his target as well), unmodified meters
over-read IR and under-read UV. The filter pack added by Zone VI dealt
with the IR, but the recommendation was to use a UV filter on both the
camera and the meter. It looks as though Romano takes the same approach
for metering for IR film.
The problem would be a lot more manageable if the spectral responses from
all manufacturers were reasonably similar, even if not perfect. Hopefully,
Kirk's tests will indicate how much of a problem the lack of similarity is.
Kirk Keyes
7-Dec-2005, 20:04
OK - here's what I came up with:
http://www.keyesphoto.com/Resource/TechInfo/Meter%20Spectral%20Scans.pdf
I placed the meter in the path of the spectrophotometer beam and adjusted the meter to give me the highest intensity with the wavelength selector set to 550 nm (a nice, bright green color). I then pressed the measuring button on the meter for about 5 seconds, and since I was in a dark room, I turned on the meter light and read the spot reading. I started at 550 nm and took readings every 10 nm going upward in wavelength until I got into the 800 and then dropped the stepping a little. When I hit 1000 nm, I then reread the values every 50 nm downwards until I hit 550, and then went back to 10 nm steps, going downwards until I got to 320 nm. I then again to check reading on every 50 nm on up to 550 nm again. The check readings were either identical to the first reading or only off by 0.1 EV. Seemed pretty repeatable.
As I mentioned above, the instrument seems to change diffraction grating order around 475 nm, and you can see there is a dip in the meter readings from 450 to 500 nm. I suggest taking that dip lightly at this point...
So in the spreadsheet, I took the EV readings and multiplied them by 0.3 to convert the measurements to density. I then combined ranges of wavelengths into "color ranges". You may disagree somewhat about the wavelengths I've associated with each color, but we can discuss that later...
I then took the wavelength densities and then multiplied them by the width of the reading steps, 10 nm usually, and came up with an "integrated area" (think back to calculus and Simpson's Approximation). These integrated areas were then summed together for each color range. The sum of all the color ranges was determined, and then a percent relative area was calculated by taking each color range integrated area and dividing it by the total summed integrated area and converted to percent.
This then gives us a percent amount of the total meter signal that would be contributed to a light meter reading of this light beam. As you can see, the IR and UV both contribute a fair amount with this meter, 10.9% and 5.5% respectively. So that means about 15% of the meter signal is form non-visible light, assuming the subject was a perfect reflector. And of course, that is with light from this bulb, which I am guessing is about 2800K. Using a 5500K light source, I would expect to have a relatively greater influence from the UV and likewise lower influence from the IR.
A friend and I compared our spotmeter this summer, using some tungesten studio lights, a Macbeth Color Checker Chart, and a piece of "black" polyester fabric. With the high IR lights, the Minolta Spotmeter F read high on the "black" fabric compared to the MacBeth black target, especially when compared to a more recent Pentax Spot V (non-Zone VI). I'm thinking of retesting the meter with a Hoya CM-500 magenta filter to see it that can pull down the IR sensitivity of the Minolta Spot-F. Just need to find one of those filters.
I'll go see if I can take my Pentax Spot V apart to get the light working...
Kirk
Kirk.... very interesting, and thanks for sharing.... I need to make sure I am understanding your graph.... Forget that 475nm hip area for now.... is this graph suggesting, that in the visible spectrum 400 - 750nm, you delivered the meter the exact same intensity light, and the EV values it gave you ranged 3 EV?
Whereas if the light meter used was the hypothetical "Ultimate Light Meter", then the meter readings would produce the same EV readings throughout the entire visible spectrum? If so, this is a huge finding? right?
Kirk Keyes
7-Dec-2005, 23:12
"you delivered the meter the exact same intensity light"
Quick answer before I go to bed -
I gave the meter light from a tunsten bulb of approximately 2800K color temp. The light then passed through the spectrophotometer which using a diffraction grating, split that 2800K light up into individual wavelengths. Then meter then made readings at the wavelengths indicated in the chart.
Your hypothetical "ULM" will always be at the whim of whatever light source it is reading. SO you need to compare the graph I presented with a graph of a 2800K light source and look for the differences. THe differences will be due to the spectral characteristics of the meter.
Jeff Conrad
7-Dec-2005, 23:30
Kirk,
Great work! Your results are quite similar to the ones I got 20 years
ago for my Minolta Flashmeter III (my meter's response was pretty much
limited to 460–710 nm, but the curve shape was similar).
Bill,
I think what you really want is a match to the film response rather than
uniform response from 400–700 nm. A good match for IR film is shown
in this
graph (http://www.davidromano.com/filteredfilmandsensor.jpg); of course, both the meter and the camera have 89B filters. A
perfect match to say, Tri-X, would be a bit more difficult because of that
film's rising sensitivity toward the UV end of the spectrum.
Again, although I'd love a perfect match that could be set to every
individual film, I could live with far less as long as the response was
halfway sensible and reasonably consistent among all of my meters. I don't
need perfection to get reasonably good exposures.
I eagerly await the results for the Spot V ...
Kirk Keyes
8-Dec-2005, 07:31
"I eagerly await the results for the Spot V ..."
I finally got the cover off my Spot V meter last night, and it looks like the bulb in it is ok - I get a continuous circuit across it, about 30 ohms, and it looks litke there is about 3+ volts going to it when I press the button. So I'm stumped at this point as to why it doesn't work...
I'll see if I can borrow a friends meter.
Kirk
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