Some information about calibrating the filters in an old thread of mine here:
https://www.photrio.com/forum/threads/making-a-multigrade-calibration-table-for-color-head.42839/
I have a Beseler 23CII-XL with the older Dual Dichro head (external stabilized power supply). I have it set up with the condensers and the conic light integrator in the head, although I have the diffusion kit as well.
I have started experimenting using the enlarger for variable contrast printing. I find that I cannot get sufficiently long exposures at the optimum lens f/stop without using the dichro filters as a neutral density filter. For example, I may set the yellow-magenta-cyan knobs (marked 1 to 200 each) to 60-60-60 to give an attenuated white light for longer exposures. This seems to work fine.
I have two questions about using the filters in this way.
The first question is whether the calibrations on the filters are linear. For example, the Arista Edu VC paper insert recommends a 10M (magenta) setting for grade #2 for "Beseler" enlargers (no model given). If I dialed the Y-M-C knobs to 60-70-60 would that give me the same (except for exposure time) contrast as 0-10-0? In other words, are the scales on the dichro head theoretically linear.
Similarly, if I achieve a good exposure using the setting 60-70-60 setting (hopefully contrast grade #2), could I change the contrast without altering the exposure by setting the dials so that the sum of the Y-M-C setting remains the same while creating the same offset of the needed color? So for example to change from Grade #2 (60+70+60 = 190) to Grade #0, with an Arista-recommended setting of 80Y, could I set the knobs to 116+37+37=190 (Yellow is about 80 more than Magenta and Cyan and the sum is still 190) and expect the exposure to remain unchanged.
Regards and thanks for any insight,
Don
Yes, the pictures are long gone from the thread, but I measured my filters with a light meter and the response was 30cc per stop and this was shown in a graph.
Depending on your lamp temperature and paper, your Cyan filter might possibly do something to the print, but I ignore the Cyan setting on all my B&W multigrade printing. Otherwise this thread could go on and on with formal diatribe on the subject.
I'm using RED as a surrogate for Neutral Density. If you swing in the Cyan filter, the RED becomes true Neutral Density. If you remove the Cyan filter, then the Neutral Density becomes RED. Since the paper is not sensitive to RED light, the more you shift to RED the less the paper gets exposed. In the first paragraph of my linked thread it mentions "adding RED" but it means shifting the filtration so it looks more red. CMY is subtractive, so technically that should read "subtracting Cyan." Ok now I have mentioned Cyan and the confusion might start. So, just ignore the Cyan dial. If the Cyan filter is in place 100% or out of place 100% the paper does not care, the wavelengths to which the paper is sensitive pass right through the filter. The Cyan filter is a clear filter as far as the paper is concerned. So if the Cyan filter falls out of your enlarger or is broken the paper won't know.
Yes, the pictures are long gone from the thread, but I measured my filters with a light meter and the response was 30cc per stop and this was shown in a graph.
Depending on your lamp temperature and paper, your Cyan filter might possibly do something to the print, but I ignore the Cyan setting on all my B&W multigrade printing. Otherwise this thread could go on and on with formal diatribe on the subject.
I'm using RED as a surrogate for Neutral Density. If you swing in the Cyan filter, the RED becomes true Neutral Density. If you remove the Cyan filter, then the Neutral Density becomes RED. Since the paper is not sensitive to RED light, the more you shift to RED the less the paper gets exposed. In the first paragraph of my linked thread it mentions "adding RED" but it means shifting the filtration so it looks more red. CMY is subtractive, so technically that should read "subtracting Cyan." Ok now I have mentioned Cyan and the confusion might start. So, just ignore the Cyan dial. If the Cyan filter is in place 100% or out of place 100% the paper does not care, the wavelengths to which the paper is sensitive pass right through the filter. The Cyan filter is a clear filter as far as the paper is concerned. So if the Cyan filter falls out of your enlarger or is broken the paper won't know.
I'm using RED as a surrogate for Neutral Density. If you swing in the Cyan filter, the RED becomes true Neutral Density. If you remove the Cyan filter, then the Neutral Density becomes RED.
The cyan filter is 'clear' to the paper. Doesn't matter what you do with it. Only your eye can tell the difference between gray (ND) and red the paper can't.Aren't these two statements saying opposite things? Just trying to grasp the advantage of using red-only to adjust exposure.
The cyan filter is 'clear' to the paper. Doesn't matter what you do with it. Only your eye can tell the difference between gray (ND) and red the paper can't.
Otherwise your next step is to get a step wedge and make the exposures. Checking things with the meter just gives one a clue where to start with the filtration. Your step wedge exposures will tell how the paper is responding. Make sure you get one with some numbers on it (1, 2 ,3 etc.) because you need to line up the same step wedge density on the processed paper test strips. You don't need a calibrated step wedge, so long as all steps are close to 1/2 step apart.
Although the cyan dichro filter does not affect the contrast, it certainly attenuates light in varying degrees. That attenuation would certainly be "seen" by the paper. It is not clear unless set to 0cc.
I get the step wedge part, though.
Best,
Don
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