difference using dichroic vs variable contrast light head?greenspun.com : LUSENET : Large format photography : One Thread
I leaned that Saunders/LPL enlargers have two kinds of heads. One is color dichroic and another is VCCE (variable contrast/constant exposure). For black and white printing, is there any difference using dichroic vs variable contrast light head? Thanks for any information.
-- Yong-ran Zhu (email@example.com), July 14, 1999
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.
-- Peter Olsson (firstname.lastname@example.org), July 15, 1999.
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.
-- Alan Gibson (Alan.Gibson@technologist.com), July 15, 1999.
Be careful using VC papers with these heads. Most VC papers are designed to be used with tungsten sources..
-- C MATTER (email@example.com), July 15, 1999.
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
-- George Nedleman (firstname.lastname@example.org), July 15, 1999.
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
-- Christopher A. Cline (email@example.com), July 16, 1999.