"john joseph" wrote in message
m...
Richard Knoppow wrote:
"Lew" wrote in message
...
Can anyone give me a run down of what's available, what
to look at &
what to avoid? Thanks.

Since others have given you some answers I will ask
a question: Why do you want to change to a cold-light
head?

I would like to know as well. I'm rebuilding a Saltzman
8x10 with condensers. I know that four 250W bulbs is going
to be hot, but such has a reliable on/off quality of
light. Cold heads - dunno - they seem so finnicky -
someone enlighten me.

Cold lights are not really finnicky but they are
fluorescent lamps and, like all gaseous discharge lamps, the
output varies with temperature increasing with increasing
temperature. While some Aristo models have heaters to even
out the output most lamps of this sort like to run hot and
run continuously.
Cold light has had all sorts of magical qualities
attributed to it. For the most part they are not so. A cold
light head is a diffusion head but so are many other kinds
of heads such as most color heads and the original Saltzman
head for that matter. For black and white silver negatives
the diffusion source produces about one paper grade less
contrast than the usual condenser head which focuses a
large, diffuse, lamp on the negative. There is no difference
in tone rendition between a condenser and diffusion source
provided that the overall contrast is compensated for either
in the print material or the negative.
Diffusion heads also tend to suppress negative
blemishes of some types but this is often illusory since the
harder grade of paper needed will tend to pick up the
blemishes again. It _does_ make a difference in color
printing where the _Callier Effect_, which is what is
responsible for the contrast difference, is very slight.
That is, a color negative or transparency will have about
the same contrast on a diffusion or condenser source.
True point sources tend to produce somewhat greater
resolution but, for the usual condenser type enlarger
source, there is no detectable difference in resolution
between the two types.
A properly designed and adjusted condenser source will
have just as uniform illumination as a good diffusion
source, including cold light sources. There is really very
little to choose between them. However, for small negatives
the condenser may allow shorter exposure times because its
light is concentrated.
I have both the original condenser source and an Arista
cold light source for my Omega D2v. I think I originally
bought the cold light because I was getting uneven
illumination. I was able to make good prints using it,
especially from 4x5 negatives. But, I eventually discovered
that the enlarger was considerably out of alignment and,
once aligned, the condenser had better uniformity of
illumination than the cold light head. For that reason and
some others, I switched back and have never gone back to the
Arista.
The D5v has a better method of adjusting the focus of
the condenser system than the D2V and should produce even
better results.
Now, the original poster may have other reasons for
wanting to switch, or perhaps the condenser head is missing.

--
Richard Knoppow
Los Angeles, CA, USA