Use of coloured filters with zone system

[vinny]

It should be noted that modern emulsions dont react to filtration the way old films did.

[Ken Lee]

Meter designers try to obtain a linear spectral response curve.

Film manufacturers try to obtain a linear spectral response curve.

Photographers try to get every exposure perfect.

Given that the color of light changes throughout the day, one could spend considerable effort trying to eliminate all possible variables, which amount to a fraction of an f/stop. By that time, the light will have changed, or the clouds will have moved.

In my humble opinion, as long as the meter isn't picking up IR or UV light, I think it should be plenty close enough.

[kev curry]

You should read about the method devised by Gordon Hutchings on metering through filters and then adding the filter factors that he advises. Its all explained in Steve Simmons book 'Using the View Camera'. Never fails and makes life simple. There will definitely be threads dealing with this if you can find them.

[Heroique]

...as long as the meter isn't picking up IR or UV light, I think it should be plenty close enough.

You should read about the method devised by Gordon Hutchings...Never fails and makes life simple.

Both Ken’s method (and Jim’s in post #2) are my field methods, but I’ve always noted that they often contradict what I “learned” from the book Using the View Camera and its section about “Hutching’s Factors” – that is, factors that one adds after metering through the filter.

According to the book, the reason to apply this “extra” factor is to help prevent under-exposed shadows. “Shadow areas,” it explains, “are primarily illuminated by blue light, and blue light is most severely curtailed by yellow, orange, and red filters.”

This additional factor is not negligible:

For example, the Hutching’s Factor asks you to take a meter reading through the filter, and then add an additional stop of exposure for filters #11 (light yellow-green), #16 (medium orange), and #21 (light red) – and to add an additional 2 stops for filters #25 (medium red) and #29 (deep red).

It recommends no additional exposure for yellow or medium yellow filters.

I suspect that even devout believers in “Hutching’s Factors” typically ignore them when their compositions contain no significant shadows.

[Ken Lee]

I am not familiar with Hutching's methods, but if we meter the shadows through the filter with a spot meter - or any other portion of the subject for that matter - there is no need to further compensate for whatever darkening the filter may introduce. We are metering it directly, not estimating.

If we only metered a standard gray card - rather than shadows lit with blue skylight - then we would miss the minus-blue effect of the filter. But that would defeat the whole point of metering through the filter: to measure directly.

If you think about it, blue skylight is not always the same color, and not always the same depth of blue. Applying a correction via formula will get us close, but measuring the shadows through the filter, is the direct method.

Short of metering at the film plane (which can be done with a Sinar metering back) that's as close as we can get, to directly metering what the film sees.

[Andrew O'Neill]

Go to this thread:

http://www.largeformatphotography.in...ad.php?t=45535

[Bill Burk]

I can't imagine a subject without an important shadow, especially since that's where I meter.

I checked spectral response of TMY-2 - it starts well-responsive to UV and blue, slopes down then drops off sharply in IR.

I checked specs for my L-758DR, no spectral curve provided but it uses silicon photodiodes and Wikipedia shows a typical spectral curve for a silicon photodiode: low-responsive to UV slopes up deep into IR then drops off - but a few hundred nm higher than the film dropped off.

I just did a quick check to see if it's sensitive to IR. Looks like it is. I'm cooking dinner right now so I pointed the meter at the electric stove on medium high (not glowing red). The hot burner in deep shadow reads 30 f/1.4 while an area in light also reads 30 f/1.4

So for blue shadows and infrared reflecting foliage, I can see where the meter is going to be a problem without IR and UV cutoff filters. So I can buy into the Zone VI Studios sales pitch.

I read the thread, Andrew, and the tests John performed are a service to the community. But I suspect metering a gray card, even a Macbeth color checker target, isn't going to tell us what's happening in subjects with excess IR and UV.

[Brian Ellis]

There was a recent thread that discussed the use of filters and the zone system extensively. Sorry I don't have a link but it would be worthwhile to try to find it by searching. I think it was within the last four or so months.

In general filters won't make a difference in your use of the zone system because all you care about with the zone system is the darkest important shadow area and the lightest important highlight area. It would be somewhat unusual, though not unheard of, for a filter to change the darkest important shadow or the brightest important highlight from one spot or area to another by enough to seriously affect your exposure or development time, i.e. the filter probably won't cause some whole new area to become the darkest or the lightest or if it does the difference won't be so great that exposure or development will be significantly affected.

As an example, suppose you're metering a red apple surrounded by green leaves. Without a filter you determine that some part of the red apple skin is the brightest important area and some part of the green leaves is the darkest. If you're going to use a red filter to darken the leaves and lighten the apple (and thereby better separate the tones with b&w film) the red filter will only make the already-brightest area of the apple brighter and the already-darkest area of the leaves darker. If OTOH you were using a green filter to separate the tones, that would cause the brightest area to become darker and the darkest area to become lighter. But probably not by enough to cause a complete flip flop or reversal of the brightest and darkest areas or to make some whole new third area the brightest or the darkest, at least not by enough to matter.

I never meter through a filter when using a spot meter, I use the manufacturer's filter factors. On balance they work out well most of the time, at least as well I think as if I tried to test myself since the conditions of the test are unlikely to be duplicated when I'm making a landscape or architectural photograph.

[Bill Burk]

Sekonic wrote me back...

The spectral sensitivity curve for Sekonic light meters begins at 430nm, peaks at 560nm and ends at 700nm.

I guess I "flooded" it with IR when I aimed it at the stove. Probably not a suitable test.

[Brian Ellis]

I am not familiar with Hutching's methods, but if we meter the shadows through the filter with a spot meter - or any other portion of the subject for that matter - there is no need to further compensate for whatever darkening the filter may introduce. We are metering it directly, not estimating.

If we only metered a standard gray card - rather than shadows lit with blue skylight - then we would miss the minus-blue effect of the filter. But that would defeat the whole point of metering through the filter: to measure directly.

If you think about it, blue skylight is not always the same color, and not always the same depth of blue. Applying a correction via formula will get us close, but measuring the shadows through the filter, is the direct method.

Short of metering at the film plane (which can be done with a Sinar metering back) that's as close as we can get, to directly metering what the film sees.

Years ago View Camera magazine published a table of compensating adjustments to be made after metering through the filter. I used the table for many years to make compensating adjustments when I metered through the filter with my Pentax 67 system. Worked great.