View Full Version : difference using dichroic vs variable contrast light head?
I leaned that Saunders/LPL enlargers have two kinds of heads. One is color dichr oic and another is VCCE (variable contrast/constant exposure). For black and whi te printing, is there any difference using dichroic vs variable contrast light h ead? Thanks for any information.
I asked a similar question in the B&W world a year back or so. In litterature the VCCE is said to provide "constant exposure", by using a combination of the coloured filter and a neutral density filter. I suppose this means that the light reaching the paper is the same regardless of filter setting. But it's still confusing, I think using one (VCCE) would be the only way to see what really happens to shadows and highlights respectively when changing the filter setting. I suspect that only the middle values retain "constant exposure". Split filtering with a color head seems to me to be a more exact way to control changes, but that requires a really sturdy enlarger so that the head doesn't move even a 1/10 of a mm when changing the filter setting.
I played with a VCCE head in a shop recently. The filters are provided for convenient B&W multigrade printing, so you adjust contrast by just twiddling a single dial, rather than looking up a table and twiddling two dials (for a colour CMY head). There was also a 'neutral density' dial, which would be useful for some purposes.
The 'constant exposure' should be defined for a single shade of grey, as it is for Ilford or Kodak filters.
I've never had success doing split grade by twiddling dials. Only below-the-lens filters works for me.
Be careful using VC papers with these heads. Most VC papers are designed to be used with tungsten sources..
The VCCE heads are supposed to render a mid grey exposure the same for all contrast settings. But what must be understood is that the light used does not produce the same spectral range that a tungsten bulb does ie #2 on a cold light does not produce the same contrast as #2 on a tungsten bulb or a #2 grded paper. You must test your own light source with a step wedge. George
I have a Saunders/LPL 4550 enlarger with the dichroic module. I do only black & white printing, no color printing. The dichroic head works great with VC paper, allowing me to have a different density range (contrast) on different parts of a single print if I need to. I used the methods outlined on Paul Butzi's web page (http://www.asymptote.com/butzi) to use the dichroic head as a constant exposure head. I calibrated it so that the same exposure time will give me the same highlight value when I change the contrast with different combinations of yellow & magenta. You could just as easily calibrate your combinations for the shadows or midtones or whatever value you want.
I believe that the only real practical difference between the dichroic head and the VCCE head is that you can get a little more magenta from the VCCE head, so you can get a bit higher contrast from your paper.
Chris Cline Salt Lake City http://risky.wcslc.edu/pers_pages/c-cline/cline.html
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