Metering through filters, exposure comensation

[Andre Noble]

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]

yes, set your meter as you normally would.

steve simmons

[bglick]

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]

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]

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]

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]

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]

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]

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]

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.