Beseler Dual Dichro head for variable contrast printing

[DonF]

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

 

[ic-racer]

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/

 

[DonF]

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/

Thanks!

I'm not so interested in absolute calibration of the color scales as to how to achieve an equivalent exposure time while varying the contrast mix.

Your example seems to indicate my proposed adjustment would work:

"So, for example, 80cc of Yellow gives ISO R (contrast) of about 120. This will eventually become M 32 and Y 112 after the neutral density (32cc RED) is added, so that the printing time matches all the others."

In your example, 80Y provides a certain contrast value. Adding neutral density involves adding 32cc to each of Y-M-C so settings become 112-32-32. This implies the dichro head has linear attenuation across the scale, as simple adding a constant to a contrast setting preserves the same contrast with a longer exposure time (higher neutral density).

A correlation would seem to be that as long as the sum of the Y-M-C values remains the same, the ND attenuation should remain constant? A little math would reveal the settings that would maintain the Y-M-C total while providing the needed yellow or magenta delta for the contrast change.

Good info!

Best,

Don F.

 

[ic-racer]

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.

 

[Chan Tran]

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

The marking of CC on the head is not very accurate. Not bad but not accurate. That is why Beseler made the 45 computerized color head with sensor inside the head to actually measure the degree of filtration the knobs have no CC marking.

 

[ic-racer]

Yes, and anyway the filter tables are approximation. Depending on how demanding you are as a printer, multiple test images might be needed for an expert print. Little off topic but I never write down the settings anyway. I have some prints from 1975 with all the information recorded in a notebook. The enlarger, paper, lens, developer, and timer (home made timer with longer than normal seconds) are no longer available. So the information is essentially useless. Plus most prints I did in the 1970s suck and I can do much better today with the same negatives.

 

[DonF]

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.

Hmm...I think I grok your terminology about using "red" as a neutral density color. In the context of a dichro head using subtractive Y-M-C controls, "adding red" means dialing in equal amounts of Y-M while leaving C out of the path completely, correct?

Therefore, one could add red "neutral density" by dialing in equal amounts of Y-M, offsetting Y or M by the recommended amount for the desired contrast grade.

For example, the Arista EDU VC paper I use calls for 60M for a Grade #3 contrast. I could dial in 0-60-0 for the Y-M-C values. If I required light attenuation, I could dial in 100-160-0. This would add additional red (as I am not using the cyan filter), which should have no effect on contrast. If each color control is linear, the overall contrast change should remain the same.

I ran some tests on the Beseler Dual Dichro head and found that a 30cc change in all three Y-M-C controls at once resulted in a one stop change in the overall brightness, as measured by an incident light meter. 30-30-30 resulted in a 1 EV reduction, 60-60-60 resulted in a 2 EV reduction, 90-90-90 in a 3 EV reduction up to the 200cc maximum.

However, each color alone did NOT result in the same change. Changing changing the yellow filter alone barely resulted in a 1/3 EV difference at the 200cc maximum. Changing the magenta control to 200cc resulted in a 1.5 EV reduction.

My conclusion is that each filter is fairly linear within its own setting range, but only equal combinations of Y-M-C result in the 1 EV per 30cc factor.

Therefore, my hypothesis that the exposure would remain constant if the sum of the Y-M-C values remained the same can not be correct.

I measured the following exposure variations for the recommended settings for the Arista EDU VC paper, using the 0-0-0 Y-M-C setting as a reference"

Grade 0, 80Y, -1/3 stop
Grade 1, 30Y, 0 stop
Grade 2, 10M, 0 stop
Grade 3, 60M, -1 stop
Grade 4, 120M, -1.5 stop
Grade 5, 200M, -1.5 stop

Best,

Don F.

 

[DonF]

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 don't understand why you would only use only red (equal amounts of Y-M) for neutral density? Using equal amounts Y-M-C provides true neutral density with more available attenuation. Also, as you pointed out, the 1 stop per 30cc change of all three filters only holds true if all three filters are used. You would need to figure out the exposure change for "adding red" separately and the relationship might not be as linear as using all three filters.

Regards,

Don F.

 

[DonF]

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.

Aren't these two statements saying opposite things? Just trying to grasp the advantage of using red-only to adjust exposure.

 

[ic-racer]

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.

 

[DonF]

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

 

[DonF]

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

Duh. You're right of course.

The cyan filter should only increase or decrease the amout of red light hitting the paper, regardless of setting. The paper is insensitive to red, so it is effectively clear, regardless of setting.

Need more coffee.

Regards,

Don

 

[Doremus Scudder]

ic-racer,

Your explanation is 100% correct, but seems a little confusing to me.

I would express things differently, i.e., saying that the paper is only sensitive to blue and green light, not red. Paper is "red-blind," meaning that whether red light is there or not makes no difference. Since the cyan filter controls the amount of red that makes it to the paper, it's basically superfluous when printing black-and-white.

Adding cyan will change what the human eye sees on the baseboard, but not what the paper sees. Since it's usually "the more light, the better" for focusing, we can safely set the cyan filtration to "0" and let as much red as possible make it to the baseboard.

And, since the paper doesn't "see" red, there's no use reducing it to get neutral density. Just dial in equal amounts of yellow and magenta, then add your filtration to that. And, yes, if you don't use cyan filtration, progressively stronger "neutral density" will appear progressively more red. I don't know if the "red quotient" is easily calibrated with a YCM head or even an accurate measure of neutral density as far as the paper is concerned, however.

DonF,

If you haven't got the Ilford tech sheet on contrast control, maybe a look at it would help. It's here: https://www.ilfordphoto.com/wp/wp-content/uploads/2017/03/Contrast-control-for-Ilford-Multigrade.pdf

FWIW, when I print VC paper with my dichro heads, I don't think in paper grades or even contrast steps. I'll do a ring-around when I need to adjust contrast by making a big change for the next test strip and then guesstimating what filtration the subsequent print will need. Small refinements are made from there. I still find that making a new test strip when I have to change contrast filtration significantly to be the fastest way to finding the final setting. Usually I want to dry several prints of slightly different contrast/exposure/etc. and evaluate them side-by-side before I make a final selection anyway. Calibrating the whole contrast spectrum is not really helpful to me, since I don't really have a "value" that I want to change a print by in mind to start with...

I hope that my stating the same thing in a slightly different manner helps some,

Doremus