DIY enlargergreenspun.com : LUSENET : Large format photography : One Thread
I am building a 5x7 colour enlarger. I have sourced a schneider g claron 210mm. i dont belive ill have any problems finding some diffusion material or a suitable housing but i was wondering if anyone out there has used 12V dichroic halogen downlights as a light source. As IR (heat)wavelenghts are passed through the reflector instead of focused into the beam i thought that would be good to use, but perhaps the removal of some wavelenghts will affect colour balance, does anyone have any ideas?
also I need to know where i can put my CC filters, is at the lights output a bad choice because of heat, or can i place the CC gels between the carrier and the lens. It would be nice to place them behind the diffuser but i cant find filters big enough to cover the full 7".
The enlarger will be used for enlarging 6cmx17cm format to up to 40' wide on ilfochrome.
-- Phil Brammer (firstname.lastname@example.org), June 22, 2001
A lot of enlargers use a 12v dichroic reflector halogen lamp, but they're proper projection type lamps, not the cheap downlighter ones. There's not that much difference in price, so you might as well use a lamp that's designed for the job.
The light from the dichroic lamp(s) is directed into a mixing chamber before passing through a diffuser. A reflection chamber is much more efficient at evening out the illumination than using a single sheet of heavy diffuser material.
A neat solution to the problem of making a variable filter system would be to use 3 lamps, filtered red, green and blue, and have them on electronic dimmers. Philips used this system in a 6x7cm enlarger, and it worked very well. It also gives you additive filtration, which is supposed to give slightly better results than the more common subtractive CMY system.
The dimmers in the Philips colour head were cross-linked to give a constant brightness, regardless of filtration.
-- Pete Andrews (email@example.com), June 22, 2001.
I would not use gel filters. I would go to the Edmunds Scientific web site and get some Dichroic filters - no worries about fading, melting, warping, etc. Plus they are MUCH more efficient than gels. Also look at the way that a Cromega Dichroic color head is made. The filters are only about a half inch square and are mounted on a bigger black metal plate. the filters are moved into or out of the front of the light but at no time do they completely cover the light - too small. The filters are availible in different sizes. Hope this gives you some ideas.
-- David Vickery (firstname.lastname@example.org), June 24, 2001.