Using CMY Controls as Neutral Density Control

[Dan Rainer]

About a year ago, I upgraded my Beseler 67 from a condenser head to a diffusion head with Dichro color filters. I mostly print small, often 5x7, so I use a neutral density filter under the lens to maintain an optimal aperture and feasible print times. This has worked well enough, but I recently had a thought—could I use the dichro filters as a sort of built-in ND?


If the paper needs a grade 3 filter for the desired contrast I would set the magenta knob to 40. Alternatively, could I set the magenta knob to 200 and both the yellow and cyan to 160? Would this still give the correct contrast, while using the remaining joint density of the three dichro filters as an ND?

 

[DREW WILEY]

With actual CMY dichro coloheads, if the filters are still in good condition and clean, then by equally adjusting (increasing) all three dials or readouts, you hypothetically get consistent neutral density. But different brands of coloheads have used different cc spacings or values. Some provide a scale or list of how much density this involves in their own specific increments, some don't. I have an easel densitometer or cc reader which makes this easy, regardless of which colorhead I'm using.

Your colorhead math is correct, but doesn't automatically mean you'll get your exact desired result. You could try it with a test strip as your starting point and see what happens.

 

[cowanw]

Page 3 here

https://www.ilfordphoto.com/wp/wp-content/uploads/2017/03/Contrast-control-for-Ilford-Multigrade.pdf

tells us Beseler uses Kodak numbers and tells you which dual controls to use.
Assuming we are talking about Black and White, Cyan is not usually used as it acts as a minus red and red is the safelight colour.
I have always found that the amount of Blue light is a more dramatic response and so multiplying both yellow and magenta by the same factor is problematic.
As you can see in the dual settings (which are meant to keep a consistent time) the difference in 0 (90 yellow)and 00 (162 yellow) maintains approximately the same time.

 

[DREW WILEY]

It also depends on if there is internal monitoring feedback to the light output, since over the long run, the main dichroic filters can degrade due to heat as well as grime build-up.
Those don't technically fade like dyed filters, but can spall off some of their coating, and eventually perform less effectively, and even a little differently from one another.

One of my 8x10 Durst colorheads has a table containing both Kodak and Durst cc increments in relation to its own settings. But in actual practice, that's only approximate. Yet when it comes to B&W VC printing, rather than color printing, approximate is generally adequate.

The ratio of sensitivity to blue vs green light varies somewhat between different VC papers.
But using my true additive RGB colorheads, instead of CMY, the green layer behaves as more sensitive. I won't go into the specific of why here; but in its practical sense, it is worth noting. CMY filtration is somewhat different, because that always includes an amount of "white" light spillover.

 

[MattKing]

It also depends on if there is internal monitoring feedback to the light output,

Definitely not in the Beseler 67 dichroic head.
Which type did you get - there are at least three?
The newest has the power supply in the head.
The oldest two I'm aware of (and had at one time) had separate power supplies feeding the head and the 82V halogen bulb inside.
One used a proprietary connector between the power supply and the head.
The other used what look like a normal plug for a wall outlet - what could go wrong???? And how do I know the answer to that question?
FWIW, when I used mine, I worked from the appropriate "speed matched" contrast setting table and just added equal amounts of all three filter settings to reduce the intensity - usually in increments of 30. 30 of course being a remnant from my days doing colour printing.
I know that the cyan was probably unnecessary, but it just seemed to feel appropriate!
Drew is almost certainly accurate about it being both not strictly linear - the contrast probably changes a very tiny amount - and the non-linearity not mattering enough to matter for B&W variable contrast work.

 

[Doremus Scudder]

For black-and-white enlarging, you don't need to dial in any cyan. The paper is blind to red, so you don't need to remove it. Equal amounts of Y and M should get you neutral density, then add whatever extra you need for contrast on top of that. That will make the image a bit easier to see too.

Since you're testing for contrast as you go, there is no need to worry about how matched the increments are, just get to a reasonable printing time with equal parts of Y and M and then find your final contrast by adding more Y or M. EZPZ.

But, since you've already got a ND filter, that's a sure thing and also easy to use. Either is fine.

Doremus