Use of coloured filters with zone system

[Curtis Lowe]

I understand how the zone system works by exposing for the shadows and developing for the highlights but what happens if I use coloured filters to further alter the tones.

How does one know how many stops a coloured filter will lighten or darken certain colours in a scene after the filter factor has been applied? For example if a green filter is used on a landscape scene, the grass will be lightened and the blue sky darkened but is there a way to measure this?

Edit: I just thought should one take their spot metre readings through the filter?

[jim kitchen]

Dear Curtis,

You ask a great question, and you will get many excellent answers...

I am not that attentive to such detail, nor do I meter through the filter prior to the exposure, but I am attentive to the filter factor prescribed by the filter manufacturer, and I apply that factor; accordingly, prior to the exposure. Experience and the filter's effect will be your friend going forward.

I found an old filter factor chart that might help you, but if you have a moment, you should search for a filter chart that is indicative of your filter's manufacturer.

jim k

[Ken Lee]

I regularly meter through the filter with a spot meter.

[Ed Richards]

Metering assumes that your film and the meter agree - which I think is true of Tmax pretty much. But it also assumes that you can see what the differences mean in your head. I would strongly recommend shooting some duplicate negatives with different filters until you get an idea of what you want. I find that the green is the hardest to judge - it does darken the sky or lighten the foliage as much I expect, despite being a pretty aggressive filter. I generally shoot two sheets for each important shot, and that lets me shoot different filters and pick which works best.

[neil poulsen]

That was a claim made by Zone VI regarding their Zone VI altered Pentax and Soligor meters. For Tri-X type films, one could meter through the filter and get accurate results.

Otherwise, one can do some testing and determine correction factors for each filter.

[Bill Burk]

Hi Neil,

You're right about that claim. I just re-read Fred Picker's newsletter describing all the problems with meters. He did correct the Sologor II for Tri-X.

His graph would scare you into buying his meter because he showed that unmodified meters are typically 1-4 stops off depending on the scene. Especially foliage gets underexposed several stops because of the high amount of infrared reflected.

One minor detail about the Zone VI calibrated meters. He put a UV blocking filter in the meter and assumes you will put a UV blocking filter on the camera too.

He claimed the UV problem is not as bad as the infrared problem, and you might be OK to ignore it. But he recommended at least using a UV filter in the mountains.

Newsletter No.37 Nov 1983 p.8

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Curtis,

Maybe it's oversimplifying Zone System filtering, but seems to me the color filter won't affect "that" color at all. For example (ignoring the infrared problem) if you use a green filter on grass, and open up two stops because of the filter factor... Then you really placed the grass two zones higher (because the filter shouldn't have had any affect on grass at all).

[ki6mf]

Agree with Ken Lee with the first to reply with meter through the spot meter. Recently while waiting for the sun to clear a building to get a shoot i metered the filters i carry against the same back ground in the same light and found that my red filter had a different reading than what the filter factor suggested! Through the Meter solves the problem.

[Maris Rusis]

A light meter can see colours very differently to film.

My Pentax 1 degree analogue spotmeter looking at a neutral surface through a #25 red filter indicates a light loss of 1.5 stops. The actual filter factor established by exposure testing on film is 3 stops. The light sensing cell in the meter is overly sensitive to red light and "thinks" there is twice as much light as is actually present.

Solution: meter the subject through the filter, calculate twice the indicated exposure, and place it on the pre-visualised exposure Zone in the usual way.

All my strongly coloured filters, red, orange, green, and deep blue have a "meter error" correction factor established by experiment. In no case is a direct meter-through-the-filter reading exactly right.

[Curt]

I found that with my Pocket Spot from Metered Light I can meter though the filter and get an accurate reading. I'm very pleased, I also have a Fred Picker Zone IV Soligor meter.

Curt

[mikebarger]

I haven't had any problems metering through the filter with my zone VI modified meter (tri-x 120 and HP5+ in 4x5).

Mike