The results are the same, but the working method is quite different. I wanted an additive Blue/Green like the Zone VI head for a long time and even tried to make something. Eventually I came up with a working method for color heads that suits me well; I've thought about trying to write that method up for some time.
I'm curious what system people use for color heads that works as well as the Blue/Green additive. I like to have the ability to adjust the highlight or shadow somewhat without new test prints (or exposure charts). I believe the additive heads accomplish that, but never did get a chance to work with one.
Using a subtractive CMY head to make the blue (er, 100% magenta) and green (100% yellow) exposures sequentially is like using an additive head. Obviously one can't make both exposures at the same time.
But it is the ratio of blue to green that is important and that ratio can be controlled by the conventional method of dialing in both yellow and magenta filtration and making one exposure.
It is possible to get identical prints either way. Some find it easier to get their heads around additive exposure and find it easier to control - split grade printing is an additive technique.
LED heads are also additive and quite easy to use for contrast control.
I'm going to guess that Mark is interested in having both colors during a single exposure, and 'riding the dials' to tweak the test prints.
You actually CAN do the same thing with a subtractive head but my personal view is that it makes the process much more complicated than it needs to be. The way it works is that the condition of both green and blue lights OFF is the same as 100% magenta and 100% yellow filtration (red, which is the same as darkness as far as the paper is concerned). To get more light to the paper you either increase your blue or green lights or you can decrease you magenta or yellow filtration. The other end of the scale would also correlate exactly being that 100% blue and 100% green bulb intensity is the same as 0 filtration on the color head.
If it is hard to conceptualize that, one can throw 100% cyan into the mix and keep it there (it won't have any effect on contrast or exposure). That way your eye can 'see' the changes in intensity. For example with 100% filtration of all 3 the baseboard will be dark, just like both green and blue bulbs being off. As you dial OUT magenta, the light will get brighter green to your eye.
Heat removal and dichroic bulb life can be an issue using the dichroic head that way, I suspect that is one reason it is not so popular.
Both 'riding the dials' and split grade printing with 2 exposures drive me crazy because the changes in mid tones are too much with any effective change in coloration.
Last edited by ic-racer; 12-26-2010 at 10:12 AM. Click to view previous post history.
That's a much better way of looking at it.
Originally Posted by ic-racer
If you set all three dials to 100% the result should be black (well, "dark", the tint depending on your head). Then dialing down the yellow filtration will produce a visible blue and dialing down the magenta will produce a visible green.
That is an interesting thought, and one that never occurred to me. I agree that it is probably not entirely practical.
I've used color heads with VC paper for a couple decades or more now. The blue/green heads just always seemed like an elegant method of working with VC paper. They don't seem to appeal to many in the responses in this thread, so I was just curious what approach other people use for adjusting their contrast with the dichro heads.
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There have been some articles about DIY LED head using blue/UV and green LEDS. I believe there was just an update to one of them using a Beseler 45 enlarger.
An obvious choice would be the Minolta/Beseler 45A color head, which is RGB additive, has a fabulous control system allowing changes of 1% or less (works in CCs), and has a great analyzer built in too. Of course it's a fantastic color printing head also, but could work for Blue Green additive B&W printing too. They go for a pittance on Ebay. I have 4 of them, one I am using and 3 spares. I don't think I paid over $100 for any of them.
Heiland electronics in Germany has a cold light solution. Unfortunately it seems the description is only in German on their website:http://www.heilandelectronic.de/html...licht_main.htm
(There's an email button on the website.)
It's made with LEDs and can be made in the formats 6x9 cm / 4x5 inch / 13x18 cm / 8x10 inch. Also special versions are possible.
PS: I'm not related to Heiland, I'm using an Aristo VCL 4500, but since these are no more available, if I'd need a replacement (fingers crossed) I probably would go for that one.