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View Full Version : Metering through filters, exposure comensation



Andre Noble
23-Dec-2005, 09:53
I read on page 27/28 Steve Simmons book about metering through filters, then adding a filter factor based on G. Hutching recommendation to of that. Question: In this case, do you still set your meter ASA to that which you would normally use, then take reading through filter? His reasning is based on insuring enough light due to color cut off in the shadows. Sounds reasonable.

My traditional way was to meter normally, then add the a filter specific factor, whci was only slihgtly larger than G Hutching's.

steve simmons
23-Dec-2005, 10:25
yes, set your meter as you normally would.

steve simmons

bglick
24-Dec-2005, 15:13
Andre, you may want to run some tests on this before actually using this technique. Metering through filters is dangerous. It's a simple test, if you using a spot meter, point it at a subject while mounted on a tripod, be sure light level is consistent....now put filter over the spot meter, it should read the value of the previous reading, minus the filter factor...but in reality, unless you are using ND filters, this will rarely happen. The reason is due to photographic light meters spectral responses curve. A large thread was on this topic not long ago. It's Russian Roullete putting filters over yoru meter, rely on the makers estimate as it will eliminate the spectral response issue.

This is also true of color temp meters. If you take a color reading with a Gossen 3, it gives you the filters to apply to acheive a color temp you desire, such as 5500K for daylight film. However, if you take these filter (s) and put them over the diffuser dome and re check the reading, you will almost never get the reading you would expect....quite often, the reading is not even close to what you would expect. Bogen describes this as the meters reaction to the filters, which is not true.... makes you wonder, huh?

Jorge Gasteazoro
24-Dec-2005, 15:34
Metering through the filter never worked for me, it always resulted in underexposed negatives. What I did is take a meter reading of a gray card and then take pictures of the gray card through the different filters at different filter factors. The negative that resulted with a density of 0.65 or close enough was the negative that received the appropriate exposure and had the appropriate filter factor for my meter/filter combination. You will be surprised how different your personal filter factors will differ from the manufacturer's.

steve simmons
25-Dec-2005, 11:02
The suggestions made in my book came from Gordon Hutchings and were carefully tested by himself, myself, and many other photographers. They take into account the reflective surface and color of the subject as well as the color of the light at the time of day the photograph is being taken.

The mfg recommendations don't do the same and neither does photographing a gray card under different conditions.

steve simmons

Jorge Gasteazoro
25-Dec-2005, 11:51
The suggestions made in my book came from Gordon Hutchings and were carefully tested by himself, myself, and many other photographers. They take into account the reflective surface and color of the subject as well as the color of the light at the time of day the photograph is being taken.

Well, perhaps you would like to explain to us the reasoning and theory behind your statement.

In my case, knowing about testing procedures and stablishing a baseline I was more interested on the relationship between the meter reading and how film responded to the filter.

According to what I read on Hutchings book the filetr factor does not change according to the light temperature or time of day, so how is really that this method takes into account the color of the subject?

Kirk Gittings
25-Dec-2005, 12:18
I have used Gordon's method for a few years since he and Steve and I taught some workshops together a few years ago. As a demo for students the second year I did a presentation to display the effect of various filters on the light sandstone and sky of Chaco Canyon and Gordon's method. Chaco is a difficult place to find the proper filter for because the right filter for the sky will wash out the sandstone etc. Anyway In putting together the demo I found Gordon's method to be very effective and accurate (with my Zone VI modified Pentax) and have used it ever since.

Jorge Gasteazoro
25-Dec-2005, 12:25
Kirk, as it was stated in another thread the fact that it works is only a testimony to the great latitude film has to tolerate errors than to a well thought out reason backed by measurable facts. What is more, this is a method that once again relies on experience and trial and error than in the scientific methodology of photography.

IMO just saying "it works" without offering any reason why it works is not the purpose of an information site. I would like to know how has this filter factor been integrated into your film developing testing? How do you know the spectral response of your film is the appropiate to the filter in question?

I am going to go out on a limb here and guess this is why Mr. Simmons does not like tabular films, because he does not know how they work and the spectral response they have.

Kirk Gittings
25-Dec-2005, 12:54
The caveats I have found with this approach is that you have to be very careful of a few things. One is touching the filter actually on the meter and abrading the filter. Gordon has solved this with a small set of identical filters. I solve it by a bit of black tape on the barrel of the meter barrel.

Also you must be very careful not to be reading thru reflections of light objects behind you too. I don't know if that makes any sense, but light objects behind you, reflected off the rear of the filter can significantly skew your reading as you meter thru it.

Also the thru the filter/factor recommendations work most consistently for me when basing the meter reading off a Z3 shadow placement for base exposure or secondarily a grey card and Z5 placement (in the same light as the subject). My concern with filtration once the proper filter is determined is to preserve shadow detail. Strong yellow/orange/red filters deepen shadows and basing the exposure on a Z3 shadow thru the filter with Gordons factors solves that.

Jorge I have seen Gordon's extensive testing records on this at his home and have confirmed his findings with my own limited testing. I initially though Gordon was full of it on this but I was wrong. It works well with the diverse films I have tested, T-max 100, FP4 and Tri-X.

Jorge Gasteazoro
25-Dec-2005, 13:54
Kirk, your example shows exactly my point, your basis for exposure correction relies on experience not on testing.

Let me give you a couple of examples. Tmx films have a greater sensitivity to red than normal films. This is why the polarizer+red filter trick does not work as well with Tmx films as it does with "normal" films (which have a greater sensitivity to blue light). They were specifically designed this way so that the rendition of "normal" skies did not require a filter. So, if you are using Tmx films and you meter through a red filter and applied an additional filter factor, you most likely obtained an overexposed frame, how much overexposed? depends on where you metered, which brings me to my second point.

If you meter a red wall through a red filter you will get a much lower exposure recommendation than if you meter lets say the shadow of the wall through the red filter. This is not taking into account " the reflective surface and color of the subject" as Mr. Simmons erroneously stated, it is simply measuring the amount of light and the color of light the filter is letting pass through, this error is further magnified by the type of color sensitivity the light meter cell has.

In contrast take my method of testing filter factors. I meter a gray card, get an exposure recommendation and add the manufacturer's recommended filter factor. With this I have done two things, established a base line and reduced as much as possible the meter cell bias towards color.

I then bracket in 1/2 stops above and below the manufacturer's recommendation and develop the film to what you would call my "Normal" development. In my case it would be an SBR of 7 or an Average gradient of 0.67.

With this step I have integrated the filter factor testing into my film developing (which I hope you will agree it is important for the tonal response) and I have obtained without relying on the meter bias a knowledge of how my film responds to the filter by measuring the density of the negative which is closer to middle gray. In addition I have introduced into the filter factor testing the tolerance levels I can live with with my film testing.

I hope you can see this is a much more integrated testing designed to reduce errors and biases than just metering through the filter without taking into account many other variables that are important. Furthermore, if someone uses the same method for developing with the same film and developer, I can provide them with the data so that they can reproduce my results without relying on experience, this IMO is the goal of testing and knowing how things work.

Saying "it works for me and many others" is a disservice if you are trying to give information to someone who is just beginning or not clear in the use and testing of filter.

Bottom line, I am not saying the Hutchings method does not work, I am saying there is more accurate and better ways to determine filter factors that do not rely on myth and anecdotal experience.

steve simmons
25-Dec-2005, 14:34
from Jorge

"According to what I read on Hutchings book the filetr factor does not change according to the light temperature or time of day, so how is really that this method takes into account the color of the subject?"

this is what Isaid

"They take into account the reflective surface and color of the subject as well as the color of the light at the time of day the photograph is being taken. "

The factordoes not change. What does change is the meter's reading at through the filter at different times of the day as the color temp of the light changes and the meter's reading changes also depending in the color of the reflective surface which is also somewhat influenced by the color temp of the light. It is a very fluid system that takes into account the changing variables that photographers working outdoors encounter all of the time.

again from Jorge

"...and guess this is why Mr. Simmons does not like tabular films, because he does not know how they work and the spectral response they have."

This is Jorge trying to pick a fight. He is completly misrepresenting my position in this matter. As I have stated many times I do not like the T-Mazx films becasue I do not get the tones I like, especially in the mid values. I also find that they are fussy and the people who do the best with them mechanically process the film so they have rigid control over time and temp and agitation. I prefer to process my films in trays.

As Kirk Gittings stated above Gordon has done extensive testing and his methods work. Jorge is a known antagonist to people who do not follow his dogma and can become abusive and insulting to people who disagree with him. This is my last post. If Jorge wants to try and fan the flames he can do it on his own. There are other successful methods beyond what he preaches.

steve simmons

Kirk Gittings
25-Dec-2005, 14:43
"In contrast take my method of testing filter factors. I meter a gray card, get an exposure recommendation and add the manufacturer's recommended filter factor."

I did this similarly for 20 plus years and found Gordon's method (with my caveat about shadow placement) much more accurate. As a rule though I never try and make meter readings off of strongly colored areas if I can help it, red or otherwise. But, I never found manufacturer's recommended filter factor to be accurate and neither did Gordon and that what drove him to devise his method.

Although I always shoot two negatives of a scene, that is for insurance against my occasional stupid processing mistakes or dust. I have not found the need to bracket exposures on either color or b&w negatives in years when in constant lighting conditions. In rapidly changing lighting conditions I do bracket for obvious reasons.

Jorge Gasteazoro
25-Dec-2005, 14:52
I did this similarly for 20 plus years and found Gordon's method (with my caveat about shadow placement) much more accurate. As a rule though I never try and make meter readings off of strongly colored areas if I can help it, red or otherwise. But, I never found manufacturer's recommended filter factor to be accurate and neither did Gordon and that what drove him to devise his method.

Well, apparently you did not read all of my post. I said I used the manufacturer's filter factor as an initial baseline, the final factor is determined by the exposure and development that gives me a negative with a density of 0.65 developed to an average gradient of 0.67.

Regardless of the shadow placement your meter cell color bias is influenced by metering through the filter. Not so in my case.

There are other successful methods beyond what he preaches.

Yep, and there are other methods which are more accurate and successful if one understands the science part of photography. I posted the metering through the filter never worked for me, and have subsequently posted my reasoning and methodology for all to see....you, on the other hand only post "it works for me" although you do not know why nor can you explain the basis of your statements.

Seems to me the one who gets upset about someone posting other methods other than what you preach is you Mr. Simmons.

Brian Ellis
27-Dec-2005, 05:45
I've never found any system of adjusting exposure for filter factors that works perfectly all the time. I've tried taking a reading through the meter, using filter factors , and taking a reading through the meter and then adding additional exposure based on the numbers in a table that was published in View Camera magazine a few years ago (I'm not familiar with Gordon Hutchings' method, maybe this table was based on his method). The latter system worked the best of the three methods with an in-camera averaging type meter but it didn't work as well for me with a spot meter.

I think there are too many variables involved to get everything right every time - differences between the film's response and the meter's response, the fact that few scenes contain only a single color, the different responses of different films to different colors (Jorge's point about Tmax sensitivity to blue skies is absolutely correct, that's one I learned the hard way), etc. Fortunately the latitude of b&w film usually makes up for these variables and I'm able to get good negatives most of the time just using the filter manufacturer's factors.

One thing I've learned (and unfortunately have to periodically re-learn) is that it's a very bad idea to put a filter on the lens, take a reading, and then forget to adjust the reading for the filter. That isn't a good system at all.