spot metering with color filters

[brian steinberger]

when shooting black and white film, i know what color filters do. so say that i want to shoot a landscape with sky. i meter the sky and place it on zone VI. that will give me a correct reading for the entire scene. but when i throw on a red filter, the filter brings the sky down to like zone IV. do i just not worry about the filter, and just take the reading as i see it? i understand the filter factor, and for a dark red filter i would add 3 stops, but that's beside the fact. but when different colors take on different tones after you've metered i'm just wondering if i should consider that when metering. thanks

[Ralph Barker]

I meter the scene, decide on exposure, and then choose the filter (or not) based on whether or how I want to modify the tonal rendition of certain colors in the scene. Then, I apply the filter factor - usually close to what the manufacturer recommended, but verified through experience and testing. There are, however, multiple methodologies by which one may divest the feline of its epidural enclosure (more than one way to skin a cat).

[Bruce Watson]

What I do, is determine my zone system exposure first. Then I add a filter, and adjust the exposure for the filter factor. In that order.

You can, if you want, use a color corrected meter such as a zone VI modified Pentax spot meter, and read through the filter. I find this method to be awkward, a good way to introduce flare into the equation (reflection off the back side of the filter and into the meter), and a great way to scratch a filter.

You should use the workflow that you find most comfortable.

[robc]

some testing would not go amiss on this.

Get a colour checker such as a Macbeth. Meter each colour on the card, note the readings down and photograph it using the reading from the middle gray reading. Then photograph it using each of your filters adjusted for their filter factor.
From your results you will then be able to see how much effect your filters are having on different colours and whether your filter factors are where you think they should be.

You can meter the prints of the results with a spot meter to compare the relative differences from your original readings but a purely visual judgement of the filter effects should tell you a lot.

[John Z.]

I beleive it makes more sense to meter through the filter. I use the technique mentioned above, with a modified Pentax spot meter, and meter through the filter. I use mainly orange, yellow, and green filters. The reason for metering is I have seen too many occasions where applying a universal filter factor would have been incorrect for the scene. For example, an orange filter in Death valley would overexpose if using the prescribed factor.

The only time you would not want to meter through a filter is if using a polarizing filter, unless you are using the filter only as a neutral density filter.

[Marko Trebusak]

Brian, I just put filter factor into equation. You must remember that all the scene will be effected with your exposure. If you meter the sky as you explained, your photo will be well expose and filter will do it's thing (reducing amount of blue colour that fall on film). If you go metering through filter, you must know what you are doing! If you meter sky through filter and place it on Z IV, you did the same thing. But if you meter sky and forget that filter will make it Z IV instead of Z VI, your highlights will go away. So IMO your method is just right, as long as you know what will filter do in your photograph.

Marko

[Brian Ellis]

Filter factors may or may not be accurate in any particular situation depending on the colors that are present in the scene and the film being used. Meters and film are sensitive to different colors in different proportions (one of the problems the Zone VI modified meter was designed to address). So neither filter factors nor readings through the filter will produce perfect exposures every time. Fortunately perfection isn't needed with black and white film.

FWIW, when I'm using a colored filter to bring the highlights down (as opposed to using it for tonal separation) I take all readings without the filter, then adjust the exposure based on the filter factor and adjust the development time based on my best guess as to the zone on which the highlights will fall when the filter is used. However, the filter factors I use aren't those provided by the filter manufacturers, they're the factors I received in a workshop based on testing. And I may make some minor adjustments to the filter factors based on the colors in the shadow areas and the filter's anticipated effect on them.

When using a Polaroid filter I just increase exposure by the filter factor. Contrary to what you sometimes read, a Polaroid filter's effect on exposure doesn't vary with the amount of polarized light in the scene (i.e. on how dark things look through the filter). The factor remains constant so just using the filter factor seems to work pretty well.

In the example you give you seem to be basing your exposure on what is usually the brightest part of the scene (i.e. the sky). That's a little unusual (though as I recall Fred Picker advocated that method). The more common practice is to base your exposure on a reading of the darkest area in the scene in which you want detail (and if you use the zone system or some variation of it, use the highlight reading to determine your development time).

[Kirk Gittings]

Gordon Hutchins has tested filtering thru filters extensively and I use his method. He has a small set he keeps with his meter and meters the shadows with a Zone III placement. His method is outlined in Steve Simmons book on the View Camera. It is the most accurate method I have found.

[Rob Vinnedge]

If you check out the Zone VI spotmeter info on Calumet's website, you will find an interesting article by Alan Ross on this question. He details what John has suggested, i.e., metering through a modified spotmeter.