View Full Version : Error in filter factoring?

Rick Durbin
9-Mar-2002, 11:21
Being new to LF, I started reading Steve Simmons' book on using view cameras. H e recommends holding the filter in front of the exposure meter when taking readi ngs, and then adding a filter factor to the exposure determined from the reading (p,28, rev. edit.). What am I missing? Doesn't this method add the filter fact or twice? Is this idea of holding the filter in front of the meter a good metho d to use?

David A. Goldfarb
9-Mar-2002, 11:33
That looks like a proofreading error to me. Yes, that would be adding the filter factor twice.

You could use the method of holding the filter in front of the meter with a spot meter or other reflective meter, but obviously not with an incident meter with a dome-type diffuser. There might sometimes be differences, though, between the spectral sensitivity of the meter and the spectral sensitivity of the film, so it isn't a bad idea to do your own tests with different films and light sources, or use the factors recommended on the film's technical data sheet, usually available on the manufacturer's website.

Steve Gangi
9-Mar-2002, 11:43
Doing that would cause you to add the filter factor twice. Either you can meter through the filter, or you can meter and then add the filter factor, but not both at the same time. I don't meter through the filter. I meter without it, and the add the filter factor. Sometimes I even remember to NOW put the filter on the lens. I'm almost as bad about that as I am about remembering to pull out the darkslide. But I still somehow manage to muddle through it :)

John Hennessy
9-Mar-2002, 14:01
Probably this second factor is "Hutchings Fudge Factor" (a la Gordan Hutchings). The concept is that the meter does one thing but it is not enough perceptually. The HFF is different for different filters right? As low as zero for some filters as I recall even if the filter's own factor is not zero. My HFF chart is in my camera case but from memory the highest HFF is less than 2x. It is not a typo.

As far as metering through the filter: that is a good idea especially if you are out under strange light (e.g., early, late, stormy etc.) but usually I just use the filter's published factor and usually use the HFF too.

Jason Greenberg Motamedi
9-Mar-2002, 14:10
Hi Richard,

I have always heard that since meters do not 'read' color and light the same way film does (particularly films like infrared, or polarlizing filters), one is best off using the published filter factor, rather than what the meter says... My own experience has affirmed this.


Jorge Gasteazoro
9-Mar-2002, 15:21
you can do it that way but the best way is to take a zone V shot with your filters and then read which negative has the correct density. For example when I use a red filter, although the published factor is 8x I use 3 and 1/2 stops instead of 3 stop, because when I took a pic of a gray card the negative that most closely came to a density of .65 for Zone V was the one with 3 and 1/2 stops more exposesure, not 3 as specified by manufacturer. Until you do a personal test you will always have a little bit of fudge factor built in.

mark lindsey
9-Mar-2002, 19:37
but isn't the reason we have to use filter factors based on the idea that the filter subtracts that particular color from the scene when put to film? How could the filter factor always be the same since that same color is not equally present in every scene.

Jorge Gasteazoro
9-Mar-2002, 20:31
Exactly Mark that is why you test with a neutral gray subject! This way you can see how much light is being substracted without worrying about the color.

mark lindsey
9-Mar-2002, 21:02
Jorge, are you saying you carry a grey card around with you and check it every time? or test once with grey card and then use that correction every time. frankly neither is very accurate since the color that you filter for will be different at every shooting session and will be different where you are as opposed to where your subject may be. why not just get an adjusted meter (zone 6) which makes a world of difference and not have to ever worry about it?

Jorge Gasteazoro
9-Mar-2002, 23:02
I disagree with you Mark, it is the most accurate way to test filter factors. I guess I will have to explain the method, I thought it was evident. Ok, I take a red filter, focus on a gray card and take 3 sheets of film, one at the manufacturers recommended factor, one at 1/2 stop over and one at 1/2 stop under, the one that comes closer to the zone V density (0.65)is my "corrected" factor. SInce you have no color you are only measuring light absorbtion by the filter. Once you are taking a real subject you are correct, some colors get absorbed and some get through the filter, but remember in adition to this phenomena there is an even amount of light absorbtion across the spectrum, which is why we use the factors. Look if you wish to continue using the factors it is not a bad way to go, but if you ever come across underexposure or overexposure you will remember what I am telling you.

mark lindsey
10-Mar-2002, 00:33
Jorge, I never said I use factors, nor will I use your method, both of which I find simplistic and inaccurate. I use a zone 6 corrected spot meter which takes care of these problems.

I and others have shown in film tests that different amounts of a color affects the factor that will correct an exposure. Can you honestly say that in the same scene if you have a dark yellow and a light yellow subject that they will transmit the same amount of light? This is why filters work in the first place!

I know why we use factors, but this doesn't totally account for this change of values.

Of the 15 years or so that I have been shooting bw I have had the adjusted meter for many years and haven't come across any under/ overexposure problems due to this method.

I understood you completly, I just disagree with you, I thought this was evident.

Steve Gangi
10-Mar-2002, 11:24
To further complicate matters, is your subject in open shade, full shade, indoors, or in full open sunlight? What about the time of day? You're starting out with different "base" color temperatures then. I suppose you could drag gray cards, densitometers, color meters, light meters etc etc etc everywhere, but why? Folks, it really is not that critical. After re-reading that section of the Simmons book, it appears he was talking about the "Hutchings fudge factor" which is an attempt to allow that meters (and filters) don't treat all colors or wavelengths the same. If they did, there would be no filtering. But again, why overanalyze everything? I and many others have never held a filter over a meter, nor have we tested everything to death, or used the fudge factor. As an engineer, there is enough testing and measuring and recording at work every day. I'd rather be out shooting. Really, lots of people shoot black and white, which is sort of a departure from "reality" anyway. Even your choice of film is a manipulation. Then factor in the different tones that each film and paper have, variations in processing, variations from one batch of film to the next, and there you go. You're doomed from the start if you're searching for the perfect definitive magic numbers. So, have fun, make the best pictures you can, but don't agonize over it. Some of the most famous photos ever made were those where the person only had time to guess at everything and expose the film.

Jorge Gasteazoro
10-Mar-2002, 12:01
Mark you use your zone VI meter in an attemp to do what I simply did with a little sensitometry. I also thought it was evident, sure different hues of a color complimentary or suplementary to the filter will overexpose or underexpose the film but, as I said there is an OVERALL light absobtion. But look you wanted to spend your money on a meter fine, I am glad it works for you, OTH just becuase you think a method is simplistic and/or inaccurate does not make it so, maybe it is because you dont understand the theory. In the end I agree with Steve G, this is a test I made about 12 years ago and have used "my" FF since then without a problem. I am glad the zone VI meter works for you but dont say other methods dont work or are inacurate when it is clear you dont understand the sensitometry and color theory.

Brian Ellis
10-Mar-2002, 20:26
It isn't a typographical error. He published a table in "View Camera" magazine a while back with the same idea. I tried it and it works very well. Filter factors aren't precise because there is no way of predicting in advance how much of a particular color will appear in a particular scene. For example, the "filter factor" when using a red filter to photograph the side of a red barn would be very different than the "filter factor" when photographing the side of a green barn with a red filter. The red filter would block very little light when the subject is red, but would block a lot of light when there is little red in the subject. So filter factors are rough guides at best. Metering through the filter is also not very precise because your meter and your film aren't equally sensitive to the same color. I've gotten much better results with orange and red filters with the sky and clouds using Steve's table (which calls for one additional stop with an orange filter and two stops with a red filter after metering through the filter) than I used to get either by using filter factors alone or by relying solely on reading through the filter with the meter. I don't know how well the method works when using it with things other than the sky, e.g. using a green filter to lighten foliage.

Steve Gangi
10-Mar-2002, 21:58
Filter factors are an approximation, probably based on some average scene. Usually, they are close enough. In the example of a green filter, used to photograph green foliage, any green portions would appear light because the filter is passing that color through. Any red colors would appear darker because the filter is blocking them. How much of each there is, the overall percentage, could be said to shift the filter factor as you say. The main thing is to know when it is time to stop testing and start photographing. For pictures of clouds and skies, the primary reason for filters is because without them the sky would just be a blank off-white patch. When all is said and done, no matter how much or how exactly you test, there are still going to be judgement calls based on how you want the final product to look - how you see it happening. That's the art.

Jorge Gasteazoro
10-Mar-2002, 22:28
Brian and Steve I agree with you completely, all I am saying is that for my film, lens meter combination I have come up with a very reliable method, now I wont go as far as Mark and tell you I have never had any under or over exposures......as the both of you stated the factors rely on many variables to be able to take into account with one test, but I sure as heck find testing more reliable than trustin a meter no matter how well it was tinkered with at Zone VI.... and for a test that I did 12 years ago, to still have reliable results no matter what meter I use....well I think I am on the right track.

Steve Gangi
10-Mar-2002, 22:47
If it works, then keep doing it. You've had enough time to know it works, and that's good. If you were not getting good results you would have tried something else, so there's no way I can argue against that. Everyone has their own approach and every person who posted had valid points, mine is just a little more casual and works for me. To be honest, my paycheck does not depend on photography, so I can afford to be a little more lax. I was more concerned with the fact that the original question was posed by someone new to large format and all of us (myself included) were maybe starting to get a little too technical. Learning is like eating. It's better to take small bites than to choke while trying to gulp it all down at once.

mark lindsey
11-Mar-2002, 20:48
Steve, if I said,"close enough" about something related to engineering would you have a problem with that? This isn't a hobby for me, and I don't put "fudge factors" on the wall. this is a big part of how I make my living, so yes, it does matter.

Jorge, if "close enough" is good for you, then thats fine, just admit it. To say that I don't understand sensitometry or color theory is laughable, especially if you knew my background and education. What you say is correct about absorption, except for the fact that you fail to compensate for variations in the amount of color transmitted by the scene. I don't know how to say it any more plain than that. If that additional variance isn't big enough for you to be concerned then thats fine, but don't claim to know what my education in these matters based on this conversation. I also never claimed to not have ever had under/overexposure problems before, I said that I haven't had over/ under problems due to filter usage when using the spot meter.

Brian, yes it is true that metering with filters in front of the meter is unreliable, unless you have a meter calibrated for that purpose. I use the pentax spot meter calibrated by Zone 6, its extremly accurate for this type of situation.

Steve Gangi
11-Mar-2002, 21:26
Mark, we have a funny saying, "There eventually comes a time to shoot the engineers and get on with production". No I would have no problem at all if you said "close enough", since engineers are expected to know when something is close enough. We call it the design tolerances. You earn a living at this, so you have to be more exact than I do. Your tolerances are more stringent. As an amateur I can get away with saying "close enough", as can most people here. You could say we have looser design requirements. I was attempting to speak from my perspective and would not presume to speak for you. There are always unavoidable variations or tolerances which must be allowed for, no matter what the field of work. One advantage to not being paid is that I only have to please myself. No budgets, time constraints, impossible customers, unfriendly critics... plus the luxury of not having to show anyone my really crappy pictures (only the good ones). Wider tolerances. More leeway in what is "close enough".

Jorge Gasteazoro
11-Mar-2002, 22:07
Mark, I fail to compensate for the color variations the same way your ZOne VI fails to compensate, why dont YOU admit it that my way is just as good and cheaper than buying a Zone VI meter. YOu seem to think that you know everything and your background of which you are so proud of allows to make the statements you made about the testing I have made. I dont know, seems to me you are unwilling to learn and listeng to new ways, plus the fact that even though you might be the greatest optics engineer you still failed to grasp the concept of filtration. SO look, I was once told dont argue with a fool, people looking at you dont know which is which, so in that vein I give you the absolute reason, you are completely correct, I AM WRONG, and I wish you luck in your blisfull ignorance.

mark lindsey
11-Mar-2002, 23:18

1.The meter compensates for both absorption and variations in color 2.no your way isn't as good because it doesn't compensate for color variations. 3.How is it that I don't grasp the concept of filtration? 4. the proof is in the pudding as they say, lets see your work.

Jorge Gasteazoro
12-Mar-2002, 00:03
LOL...if I dont wish you argue with you any more, what makes you think I am going to get into a "I'll show you mine if you show me yours" deal?? 1.- since you rely on a gizmo to do your thinking, I have no interest on either showing you my stuff or knowing your opinion. Please read my statement about arguing with a fool! 2.- I have admited to all you are correct, so this will be my last post on this matter, have a good life Mark!

Photo Bob
12-Mar-2002, 00:10
If Mr. Lindsey makes a living from what he shows on his web site, I would think that he would starve.

Steve Gangi
12-Mar-2002, 00:34
I'd actually enjoy seeing this "Big Shootout" and would be willing to toss in one or two of my own, just for laughs. I wouldn't expect to win, have no great secrets to pass on, there's no pressure on me, so what the heck. Just be warned, I'm a stubborn SOB who's been playing with film since the late 50s so no matter what, I will still do things my way. Now, how do we do it?

13-Mar-2002, 23:29
Enjoying reading this thread. I learned a lot. One question though:

Am I correct that published filter factor is based on Zone V ? And we usually expose for Zone III/IV ....

An accurate filter factor should be the one that makes Zone III/IV as it should after a filter is applied ....and it certainly is not the published factor, Yes ? No ?

Regards, C.J. Wong

Jorge Gasteazoro
14-Mar-2002, 12:12
C. J. Not necesarily, if you wish to test for your factor I would test for zone III or IV since these are the zones with the most important information, in addition I would do it in the shadow to recreate the color most likely to be present when you photograph. When I did this I used a color chart and it was great for information so I would use this too. I did it for Zone V because I calibrated my printing times to ZOne V as opposed to Zone I as most people do.

Steve Gangi
14-Mar-2002, 22:07
Hahaha I see another argument in the making :) For *negative film* the general approach is to meter for Zone 3. You decide which area is the darkest one for which you want to keep detailed. Then, you adjust the development for the highlights. This is what Ansel Adams says in his books. For slide or transparency film, the general practice is to meter Zone 7. If you are as lazy as me, then measure the dark area and the light area, see what the spread or "scene brightness range" is. Then depending on the spread, decide what you are willing to block up, blow out, turn into mud etc. Let the games begin!

Jorge Gasteazoro
14-Mar-2002, 22:41
Actually Steve I agree with you, and when I am in a hurry I do the same as you, check the spread and decide on developing. I guess I should not have assumed C.J. was using B/W neg film. With transparency you are correct and should meter for the highlight thus CJ would have to tailor his method depending on what he is using.

Steve Gangi
14-Mar-2002, 22:51
Well, you said you calibrate in order to get a good print. That's the whole idea anyway, so you are right. It seems a lot of people are using color slide film though, so that's why I brought it up. When there is a chance to get an exceptional picture for showing off at work, I generally use TMax 100 and before shooting, my favored way is to meter, double check, take a test Polaroid (Polaroid 54 is a nice proofer for TMax 100), and then shoot. The two films don't have exactly the same characteristics, but this makes for a good "sanity check". Tmax is sort of sensitive to changes in development time/temperature though, so consistency is a must.

Jorge Gasteazoro
15-Mar-2002, 23:59
Yes I calibrated with both TMX and TMY, but now after I tried ACROS on 8x10 I am getting away from TMX. It does not blow the highlights as easily as TMX does, the only problem is I have not been able to find it in 4x5 which is my format of choice for enlargement. BTW ACROS with filters looks great, you are going to get beautiful skies if you use an orange or red filter.

Steve Gangi
16-Mar-2002, 11:31
Do you have a good paper cutter? If so you might be able to cut the 8x10 sheets down. I never tried it, but others have. And yes, TMax is a bit "contrasty". But, sometimes you get something that makes you say "Oh yeah". It's great in shots where you want to "pump it up" a little - just like Velvia can "pump up" a bland scene in color.

Jorge Gasteazoro
16-Mar-2002, 11:57
Yeah I have a good paper cutter, but I tried that before with Pan XX and needless to say it was not a big success....... I guess I just will keep checking Badger until they have it.