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Single v dual filter settings

David Lingham

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Is there a discernible difference in tonality between the single and dual filter settings for a dichromatic colour head when printing on multigrade paper? I have been using a dichro head on my De Vere 203 with VC paper for well over 25 years and have always used the Kodak single filter numbers appropriate to the De Vere. Recently I had to make a series of small prints (5x7) and found the exposure time from the single numbers were too short for any print manipulation. In order to create a longer exposure time for dodging and burning I switched to the dual filter numbers. I subsequently noticed a very slight improved smoother tonal response at the same grade settings, to my eye the difference is only very marginal and would probably be lost if I tried to upload any examples. My theory, and please prove me wrong, is that whereas the single numbers use either the hard or the soft contrast emulsion layer in the paper, the dual numbers use both. For example, grade 3 in single numbers is 25 magenta, grade 3 in the dual figures is 23 yellow 56 magenta.
 
No, there won't be a difference. But using multiple filters you can end up with a slightly different contrast grade due to imperfections in the filers themselves and/or the translation tables used.

David Lingham said:
dichromatic colour head
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'Dichroic'. Dichromatic would be something else. The filters are dichroic, which means they're basically interference filters that work by the selective reflection of certain wavelengths in a very thin metal layer that's deposited on the glass of the filters. This sets them apart from e.g. gelatin filters that use dyes for selective absorption. Dichroic filters are more durable and generally better resistant to heat. Sorry for the nitpicking.
 
What you are doing kind of makes sense, when using a dichroic enlarger for colour and we wanted longer times we would use three filters by incorporating the cyan filter as well. For Black and white I think you are achieving the same thing with your method, as far as a smoother transition of tones with two filters I never heard of this but maybe you have noticed something of value.
 

seems logical. However, the way I understand it, there are no different contrast layers in Ilford's VC papers but a single layer containing blue and yellow sensitive components with different contrast behaviour, which would call for no difference between single or dual filtration.
 
RalphLambrecht said:
there are no different contrast layers in Ilford's VC papers but a single layer containing blue and yellow sensitive components with different contrast behaviour
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I've been corrected on this a few times, so I've stored it in my memory - this is not the case. It is indeed a single emulsion, but in the case of Ilford's Multigrade paper, there are 3 light-sensitive components, each of the same contrast, but they vary in the degree to which they are sensitive to green light. All three components are sensitive to blue light.

The Science Behind Ilford Multigrade

rps.org
 
David Lingham said:
Is there a discernible difference in tonality between the single and dual filter settings for a dichromatic colour head when printing on multigrade paper?
Click to expand...
koraks said:
in the case of Ilford's Multigrade paper, there are 3 light-sensitive components, each of the same contrast, but they vary in the degree to which they are sensitive to green light. All three components are sensitive to blue light.
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I've asked myself a similar question for a long time, in the specific case of the Ilford MG papers., An optimum D/logE curve is obtained by the relative shifting of the three emulsions (in a single layer). As the "hardness" is modified the D/logE curve of the intermediate (green/blue) emulsion should move towards/away the D/logE curve of the blue-only emulsion at half the rate of the green-only emulsion. Once general exposure is accounted for, this requires two degrees of freedom, that must be properly coordinated to achieve a proper curve at the intermediate grades.

Now, with a dichroic color head, or a blue/green LED head, we have (again, once general exposure is accounted for) just one degree of freedom. Maybe the resulting shifts of the three D/logE curves will be near optimum way, maybe not. One might imagine that the Ilford MG filters are carefully engineered in that respect.

In practice, nobody has seen a demonstrable difference. And then there are Foma papers: two or three emulsions?
 
koraks said:
Dichroic'. Dichromatic would be something.
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Koraks. De vere in their manual call the colour head a Dichromat, my apologies the typo was predictive text.
Thank you Bernard, I think I understand.
 
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Thank you Bob, I forgot about adding cyan filtration. I believe it’s 30 for one stop.
 

Thanks for the reply Ralph
 

I believe what the OP is seeing is simply a slightly different characteristic curve between single and dual filtration. As he says, the difference would probably get lost in the upload.
 
koraks said:
What does that mean, specifically?
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Come on. You know what an HD curve is about. Depending on filtration, they are different, and so is the look of the print.Single and dual filtration could have the same paper contrast overall, but ondividual portions of the curves could be slightly different.
 
To the best of my knowledge, so far nobody has ever shown a convincing analysis nor practical examples that illustrate this. Hence the question; you seem to be adamant that these differences exist, so let's see them. If possible, please also explain how the paper 'knows' the difference between the same wavelengths coming through an overall denser or less dense filter pack.

To the contrary; what experiments have been done and also reported on including here on Photrio have always shown no practical/visible difference between split grade and single grade exposures. Just like the theory would suggest.

Like I said, the likely difference at work is just a slightly different grade due to side-band absorptions of both magenta and yellow filters, which will likely be a little different, and therefore the net result will be a different paper grade. We're probably just looking at an overall 0.5-1 grade difference.
 
Question is more if the both filter tables of Ilford are correct (what I guess) and if your enlarger set up fits the Kodak/Durst/Agfa values what is more the question. Is mor what you want to see on the paper than knowing that my picture is grade 2,5. The real difference between 1 and 2 filter mode us that with two filters, you need less enlargement time adjustment with changing the grade - as far as I understood the whole thing. I personally use either an Analyzer with under-the-lens filters even if my 4x5 Homrich has a color head or a multigrade head with test strips for splitgrade or traditional enlarging or an Heiland automated splitgrade system.
 
The paper sees the same color, irrespective of single or dual filter combination. Adding Y to M or adding M to Y is "seen" by the paper as adding in neutral density.

One can empirically verify this with any "Color Analyzer/Exposure Meter."
 

You are right, It needs a proper test and comparison to verify my claimbut thiall depends on how accurately the published single and dual filter numbers actually produce the same paper grade and how closely our enlarger filter settings match those used by Ilford. I suspect some difference there too. I will be hard to set up a valuable experiment. No argument from me, by the way, on single-filter vs split/grade filtering.
 
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