There are really three types of heads, condensor, cold light, and diffusion.
(well, there is point source, but that's for microfilm) Diffusion is a
relatively new thing.
I recently replace the variable condensor head on my D2 with an Ilford 500
VC diffusion head. Diffusion light sources are the common type in color
heads. If you've ever had a color negative hand printed by a pro lab, it's
99ure it was on a diffusion head. People have translated color filtration
to VC filter settings, but success is limited, as you can't get a full range
with the normal color printing filters. Then, Ilford (and others?) made a
head that is of the same design, but for VC paper. Two bulbs project light
through dichroic filters into a mixing box, with a piece of opal plexiglass
on the bottom. This is the head I have been using for about three weeks.
I find that the contrast is indeed less than with the condensor head.
Scratches are reduced, although not eliminated, and dust is hardly affected
at all. The great advantages are the ease of changing filtration (especially
for split filtration), and the fact that the negatives are not heated, and
don't pop as readily.
Cold light heads are a different animal. They use flourescent tubes, and
require the same VC filters as a condensor head. If buying one used, be
careful. Special tubes are required for VC paper. Uneven or inconsistent
light can be a problem without a compensating timer.
Bill Pearce
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