Metering through filters

[Kevin Kemner]

My question is about metering through filters. I recently returned from a photo trip where I decided to try metering through the filter rather than adjusting t he exposure according to the filter factor. (as I normally do) Now that I'm dev eloping, the shots where I did this are fairly underexposed. I'm guessing about one stop to two stops depending on the filter. I use a Gossen Luna-Pro F with the variable angle attachment and Bergger film developed in Pyro. I haven't had problems with this combination before so it must be the change in technique. D oes anyone have any thoughts?

Thanks

Kevin

[N Dhananjay]

The spectral response of film often differs from the spectral response of the meter cell. Which means readings from brightly coloured areas or through a filter must be interpreted with care. Typically, metering through a red filter will underexpose by about 2/3 stop with most panchromatic film, depending on the meter cell. Filter factors are based on the reproduction of a middle grey. Personally, I don't even know if filter factors are necessarily the best compromise either because in many shooting situations, I find the effects of filters on local contrast extremely difficult to predict with any precision. For e.g., I know that a red filter will darken a blue sky but I'm never able to predict by how many zones it will darken the sky. I sort of makes stabs at it by metering with and without the filter. That, I think, is the information metering through a filter can perhaps give you. However, for exposure, the filter factor is perhaps a better compromise to make, at least for most field shooting situations. If I have a very complicated (for me) subject, I take the lazy way out and shoot a couple of sheets and develop them one by one. DJ

[Ron Shaw]

I also find that metering through the filter doesnt give me the proper compensation factor. When I first started using a polarizer, I metered through the filter and it gave me a 1 1/3 stop factor, but using 1 1/3 stop still gave me an underexposed chrome. By trial and error, I finally came to a 2 stop compensation factor, which seems about right (for my polarizer, anyway). So... good idea, it just doesnt work!

[Sean Billy Bob Boy yates]

And so the spectre of Zone VI modified meters rears it head....

I believe it was Gordon Hutchings that developed a filter factor technique that has been published in Steve Simmons book, Using the View Camera and also in View Camera magazine, It may be on the V.C website. If interested I can look it up for you so e-mail me.

[Mark Brown]

Not much to add, except to say that I too have found metering through filters to be not as reliable as I would have thought, esp. for polarizers. Could be due to spectral sensitivity of the film, meter, or whatever. Now I shoot according to the data book (colour compensation filters only, no black and white work) and it seems to work.

[Robert A. Zeichner]

At what are you aiming the meter when you take a reading through the filter? If you were to aim the meter at a target that was the same color as the filter, the filter would transmit most of the light striking it. On the other hand if you were aiming at a complimentary colored target, the filter would block far more light. A good illustration is the technique commonly used for shooting sand dunes at dawn. Yellow filter, no compensation, place highlight of dunes in Zone VI, give N+1 development. The lightstruck areas of the dunes are very near in color to the yellow filter. The filter passes pretty much all of that light. The blue light in the shadow area is partially blocked by the yellow filter, creating a thinner negative in that area. This, plus the extended development, which pushes areas placed in Zone VI into Zone VII, enhances the contrast of the negative, thus transforming what, in color is somewhat flat, into a contrasty, dynamic black and white image. Perhaps aiming the meter at a grey card would yield exposure offsets that would more accurately reflect the specified filter factor. One other note: Very often a filter's factor is a suggested range as opposed to a single number. Depending on the spectral response of the film, the color temperature of the light source or some of the other variables (like the color of the subject) can influence the practical factor for that situation.

[Chris Partti]

For more than you ever probably wanted to know on this subject, see http://members.aol.com:/workshops5/zsfilter.htm.

[pat j. krentz]

Hint! I have a Zone VI modified spot meter (Soligor) which give me very accurate readings in all light situations, with and w/o filters. Pat

[mark eban]

Hate to say it but the modified Zone VI meter really does let you meter accurately through the filter....

[Doremus Scudder]

I have to agree with the Zone VI meter faction here. I own two modified Zone VI meters, a Soligor and a Pentax digital, and routinely meter through them with go od results. There are, however, some other factors which affect film speed, etc. to be considered when using filters besides matching the spectral sensitivity o f the meter to that of the film one is using. A look at the spectral response cu rve for any B&W film will show you that the film is more sensitive, i.e. faster at certain wavelenghts and less sensitive, or slower at others. A sharp cutting red filter (that means, photographing with red light only) can slow some traditi onal B&W films by up to three stops! Other colors have different effects. This i s also the reason why B&W films have different speeds in daylight and tungsten l ight. One could get very scientific about the whole thing and compare spectral c urves of filters and films and different phot cells and probably earn a Doctorat e at RIT. Empirical testing, which takes much less time, shoud get you in the ba llpark so that you can use your meter to read through filters (whatever it is, b ut I recomment the Zone VI since it approximates the sensitivity of B&W films mo re closely) and then apply the appropriate film speed "fudge factor" which has been determined from tests. Contrast can also be affected, so test that too, you may need a development factor as well. Using filters is unpredictable and inexact, but one can reduce the inconsistenci es significantly and have a practical working method that produces consistently printable negs. For more info see David Kachel's article on exactly this subject . You can find it and many other interesting articles at: http://members.aol. com/workshops5 Hope this helps. ;^D)