Stacking filters - how many is too many?

bvy · Feb 21, 2019

For color printing purposes, I'm wondering what the difference is in using say a CP40M filter versus stacking four CP10M filters? Does the stacking add neutral density? I think it must but I'm wondering if it's negligible. Thanks.

Kilgallb · Feb 21, 2019

More than one means a chance of Newton’s Rings. Each filter surface interface will cause up to 12% loss. So two filters means two more surfaces or up to 24% loss unless there are anti-reflective coatings on the filter.

bvy · Feb 22, 2019

Kilgallb said:
More than one means a chance of Newton’s Rings. Each filter surface interface will cause up to 12% loss. So two filters means two more surfaces or up to 24% loss unless there are anti-reflective coatings on the filter.

Why would Newton Rings matter when making a color print? Typical application is at least two already...

Photo Engineer · Feb 22, 2019

You will see Newton's Rings as colored patterns.

But, each filter does add density and thus exposure must be increased.

PE

DREW WILEY · Feb 22, 2019

Are the filters going to be in a drawer above the negative carrier, or used beneath the lens? It makes a big difference. The effect of rings between sheets in a drawer can be minimized by adding a sheet of frosted diffusion mylar beneath the filters. For below the lens, you should acquire specific cc high quality glass filters if you want the best results.

pentaxuser · Feb 22, 2019

I thought bvy's question was whether the additional exposure caused by a CP40M was the same as 4 CP10Ms Intuitively I'd have thought the effect to be the same. What would cause it to be different?

Presumably one filter from an interference aspect is preferable?

pentaxuser

Photo Engineer · Feb 22, 2019

Each filter has a small but real effect on exposure. Part is due to the substrate of the filter and the other part is due to surface reflections.

PE

pentaxuser · Feb 22, 2019

Photo Engineer said:
Each filter has a small but real effect on exposure. Part is due to the substrate of the filter and the other part is due to surface reflections.

PE

So my inference from your reply is that 4x10CP10Ms do result in a different exposure from 1 40CP40M. I take it that 4 x10 is greater than 1 x40 but it is not possible to calculate by how much? It is "suck it and see"

Thanks

pentaxuser

DREW WILEY · Feb 22, 2019

A darkroom meter with time readings or perhaps even a lux meter would give a clue. An easel densitometer, though pricey, works superbly if you combine it with a basic ten buck high school math calculator that works in log units. Otherwise, just adjust the lens opening and match test strips. How much simpler can it be than that?

Photo Engineer · Feb 22, 2019

It is possible to calculate by measuring the density of one filter and multiplying by 4 and then measuring a 4x filter. There is a difference but it implies that you have these filter combinations to measure. I have them. You may not.

PE

pentaxuser · Feb 23, 2019

OK and thanks PE. I have learned something. From a practical exposure point of view would the difference between 4 x10M and 1x40M be enough for it to be obvious or would most viewers see the "same" print to all intents and purposes?

pentaxuser

Photo Engineer · Feb 23, 2019

OTOMH, IDK! I would have to measure the densities of both packs. You see, it may vary from manufacturer to manufacturer and etc.... It could be anything from 1/8 stop up.

PE

pentaxuser · Feb 23, 2019

Thanks PE. Ralph Lambrecht and maybe quite a few others believe themselves capable of distinguishing between shots where the exposure is as little as 12th of a stop different but this, I think, was with reference to B&W prints. I know that excludes me and I suspect a lot of others and it makes me wonder if a difference of 1/8th stop has the same/more/less impact in a colour print. I suspect less but that is simply a "gut feeling" as they say on my part.

pentaxuser

Photo Engineer · Feb 23, 2019

There is a difference between a camera exposure that is off, and a printing exposure that is off. It is subtle, and possibly it can be ignored, but in the negative that is underexposed, the information is not there. In this case, the information is there but not available due to the filter. It can be revealed by selective dodging or it may just come through in the print. IDK for sure.

PE

Stacking filters - how many is too many?

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