On the "Contrast Control" fact sheet for Ilford multigrade papers, there are two methods of contrast control for colour heads: single filters and dual filters.

Under single filters, for Kodak filtration, Grade 00=199Y.
Under dual filters, for Kodak filtration, Grade 00=162Y/0M.

I don't get it. On my Devere head, dialing in only 199Y implies 0M, i.e., I set the magenta filter to 0. So, why when it is dual filters does this value change to 162Y even though magenta is still 0?

As usual, I hope this is not the stupidest question in the world for today.

2. ## Re: colour head/b&w printing

Copy editor fell asleep? Either that or they are trying to speed match.

I doubt you'll see any difference between 160Y and 199Y. Maybe with a densiometer. But just maybe.

3. ## Re: colour head/b&w printing

This might be a fun question to post for Simon Galley over at APUG.

4. ## Re: colour head/b&w printing

I found no difference on a Beseler color head between 120Y and 200Y on Ilford paper, just extra neutral density.

5. ## Re: colour head/b&w printing

Originally Posted by Nick_3536
I doubt you'll see any difference between 160Y and 199Y. Maybe with a densiometer. But just maybe.
Maybe, but that is not the point. Let me give another example:

for single filtration, grade 4 1/2 is 140M (which would imply 0Y, right?)
for dual filtration, grade 4 1/2 is 0Y/150M!!!

I am thinking that your first observation about the copy editor might be right. But am I the FIRST person to notice this? Geez.

6. ## Re: colour head/b&w printing

The Illford charts are correct.

With a color head, a given contrast level can be obtained by many different color combinations. Using diffferent color combinations on a color head also produces changes paper speed (sometimes big changes in speed!) because the filtration is not density corrected as it is in filter packs.

The dual filtration values listed on Illford’s spec sheet are speed rated, and are designed to be compared with other dual filtration values to obtain different contrast levels using approximalty the exposure time. Comparing the single color table and the dual color table reveals an apparent paradox where, given the same contrast level, the dual filtration values (using only one color) differ from the single filtration values. This is OK, because at the paper’s very high contrast end, 4+ and over, and very low contrast end, 0 and lower additional color filtration has little marginal affect on contrast but still has some effect on exposure time (see John’s example where dialing in additional yellow has no effect on contrast but does have an effect on time because of the additional “neutral” density.)

7. ## Re: colour head/b&w printing

David, sorry. I just don't get it. I am standing in front of my Devere 504 dichroic head. I will now dial in the single filtration value for grade 00, which Ilford lists as 199Y. So, I set the cyan dial to 0, the yellow dial to 199, and the magenta dial to 0. I will now set the DUAL filtration value for grade 00. I set the cyan dial to 0, the yellow dial to 162 and the magenta dial to 0.

Let me recap the settings the three dials on the head for both single and dual filtration:

0C 199Y 0M - settings for single
0C 162Y 0M - settings for dual

I don't get it. What am I missing?

8. ## Re: colour head/b&w printing

David is proposing that the contrast is the same, but the exposure time is not. The non-constant exposure chart doesn't need to worry about keeping the time consistent, so for that one there's no reason not to go with less filtration and shorter exposure time.

Very interesting hypothesis - easy enough to test...

9. ## Re: colour head/b&w printing

Don - You'll get 00 contrast for both of those settings! The exposure time will probably be different for each. Its the way the various emulsion layers work on VC papers. Contrast is based on the relative proportion of blue and green light that hits the paper. Once you hit a certain threshold of yellow filtration, adding more yellow has no effect on contrast because you've already maxed out the amont of green light the paper can take. (more yellow filtration = more green light = less contrast).

10. ## Re: colour head/b&w printing

David, I get that now. So why did Ilford put two different numbers when there is no difference? Just to confuse me? If so, it sure worked.

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