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Compatible Cold light heads for Omega D5V



 
 
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  #1  
Old June 5th 09, 12:48 AM posted to rec.photo.darkroom
Richard Knoppow
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Posts: 752
Default Compatible Cold light heads for Omega D5V


"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?


--
Richard Knoppow
Los Angeles, CA, USA



  #2  
Old June 5th 09, 02:09 AM posted to rec.photo.darkroom
john joseph
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Posts: 3
Default Compatible Cold light heads for Omega D5V

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.
  #3  
Old June 5th 09, 03:46 AM posted to rec.photo.darkroom
erie patsellis
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Posts: 35
Default Compatible Cold light heads for Omega D5V

john joseph wrote:
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.


*waves wand* I pronounce you enlightened....as if my opinion really mattered (been married
too long to think otherwise)


I think most people want to go to a diffused light source to minimize the dust and scratch
issue. Personally, I lean towards the flourescent bulb and white diffusor approach, which
reminds me, John, you wanna let go of that electromagnetic (solenoid actuated) shutter
from the enlarger?

back to the subject at hand, if you know a good (I mean really good) neon bender, a
coldlight head is not much more than a neon tube bent in a serpentine pattern. I bent one
up (years ago) for a friend that had vertical returns and had 1/2" spacing, used a bit of
glass up, but worked wonderfully. It's really important to ask you bender to bombard the
glass properly, most glass guys just seem to do good enough, as opposed to allowing all
the contaminants to be burnt off before pumping the glass down. I could probably look up
the specifics if anyone is interested, I may have my notes still.

e
  #4  
Old June 5th 09, 03:52 AM posted to rec.photo.darkroom
Richard Knoppow
external usenet poster
 
Posts: 752
Default Compatible Cold light heads for Omega D5V


"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



  #5  
Old June 5th 09, 11:04 AM posted to rec.photo.darkroom
Jean-David Beyer
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Posts: 245
Default Compatible Cold light heads for Omega D5V

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?

Richard's implied suggestion is a wise one. All manner of magical properties
are ascribed to cold light heads.

The most important one is supposedly that you can use it to print negatives
that are unprintable otherwise because their contrast is too great. Of
course, that should seldom arise because you calibrated your exposure,
developing, etc., to your existing enlarging system already, right? So if
your negatives have excessive contrast to print even on the softest grade
paper, you mane a serious mistake in exposure, or development. Picker seemed
to feel that exposing and developing for (IIRC) grade 3 paper and printing
with a cold light gave better quality prints than exposing and developing
for grade two paper and printing with a condenser head. But as Dr.Richard J.
Henry proved, the two will have identical D/H curves. So this argument turns
out to be of no validity. A cold light head will be helpful in controlling
contrast only for those who overdevelop their negatives. It was my
impression that people used to underexpose their negatives (they thought
they were increasing the speed of the film), and over develop them to
maintain contrast in the mid tones (only to get burned out highlights). But
if you calibrate your film, you will get the best speed of which the film is
capable (but not 800 from Tri-X; probably not even 400).

The next most important claim is that with diffuse illumination, dust and
other defects of the negatives simply disappear. This turns out to be
nonsense. Picker's most important cure for this problem is not his (or
anyone else's) cold light head, but his negative cleaning brush, the one
with a 5000 volt neon sign transformer that produces a corona near the
bristles of the brush with which you wipe the dust off the negative. A cold
light head lowers the contrast of your print by about one contrast grade
compared with what you would get if you used a condenser head. But then you
have to use a grade harder than the condenser head required to get the
proper contrast, and the dust and scratches are back. Sorry, the only good
solution is to keep your negatives clean, or to clean them.

As far as I can tell, the only reason to use a cold light head is that it is
somewhat cooler than the typical condenser head. This can reduce the risk of
the negative's popping between when you focus it on your paper and when you
actually make the print. I have never had this happen, but I do not doubt it
can happen, especially with small negatives (e.g., 35mm). It does not happen
for me with 4x5" negatives because I use Beseler's Negaflat (I call it their
nega-stretch) film carrier there that puts the film under slight tension so
it must be flat. Others call it their nega-scratch carrier because it tends
to scratch the extreme edges of the negative. I do not compose my images
quite that close to the edge of the image area, so it does not bother me.
For other sizes, you might consider using glass holders (I forget what they
are really called: the ones where the film is held between two pieces of
glass) that should also keep them flat.

If you get a cold light head with two tubes, a blue one and a green one, you
will not need to bother with variable contrast filters to get the contrast
grade you need (if you use variable contrast paper). You just dial in the
amount of blue and green you need to get the contrast you want. I find this
a convenience, but a color head would do the same thing. Aristo still make
these, and Zone VI used to. The main troubles with the Zone VI are that the
thing is not really bright enough, though it is definitely usable; and that
the green tube has to be warmed up considerably to get the regulator to keep
it stable, which is annoying. I hope that the Aristo does not suffer from
this problem.

--
.~. Jean-David Beyer Registered Linux User 85642.
/V\ PGP-Key: 9A2FC99A Registered Machine 241939.
/( )\ Shrewsbury, New Jersey http://counter.li.org
^^-^^ 05:40:01 up 72 days, 11:54, 3 users, load average: 4.12, 4.16, 4.07
  #6  
Old June 5th 09, 01:23 PM posted to rec.photo.darkroom
john joseph
external usenet poster
 
Posts: 3
Default Compatible Cold light heads for Omega D5V

erie patsellis wrote:
john joseph wrote:
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.


*waves wand* I pronounce you enlightened....as if my opinion really
mattered (been married too long to think otherwise)


I think most people want to go to a diffused light source to minimize
the dust and scratch issue. Personally, I lean towards the flourescent
bulb and white diffusor approach, which reminds me, John, you wanna let
go of that electromagnetic (solenoid actuated) shutter from the enlarger?


If you mean the one I diagramed, then sure. It won't work at all with my
timer. It is in pieces now. I think you have my email address. Write and
I'll try to make it so.


back to the subject at hand, if you know a good (I mean really good)
neon bender,[...]


Funny you should ask. I DID know one but he fell deeply into alcoholism
twenty years ago and is good for nothing now except some good story
telling - over and over and over. No benders anywhere near here.
  #7  
Old June 5th 09, 10:53 PM posted to rec.photo.darkroom
Richard Knoppow
external usenet poster
 
Posts: 752
Default Compatible Cold light heads for Omega D5V


"Lew" wrote in message
...
I replacing a Zone VI VC enlarger & head which after some
years of
reliable service seems to be becoming finicky. I'm fairly
certain the
electronics are not repairable, not to mention the prospect
of
replacing bulbs when that time comes ... or even evaluating
if that
time has come already. In any event, I have many years of
negatives
developed to a contrast level suitable for a cold light
head. This
creates the possibility that negs which I've printed on
harder paper
in the past will not print well in the contrast ranges
afforded by my
new enlarger with condensers. The simplest solution I could
think of
was to scale back my development times for new work, but to
get a cold
light head so as not to lose any flexibility printing my
older stuff.

Since it seems likely that this thread may go on to ask how
I chose
the Omega, I'll answer now: It has no more electronics than
a common
lamp and the bulbs aren't much harder to find either. I
can't envision
a time when this enlarger would become unusable.

For the most part I have had no difficulty in printing
the same negatives on either type of head. While variable
contrast paper does not _exactly_ duplicate the curves of
graded paper it comes close enough and can be adjusted over
a very wide range.
The difference in contrast depends on the design of the
head. Most condenser heads are partially diffusing because
the source is usually a large lamp with a highly diffusing
(opal glass) surface. This has the effect of lowering the
Callier factor and also makes focus of the condenser system
less critical. Ideally, the condensers should focus the
light on the entrance pupil of the enlarging lens. Probably
the best way to check for focus and alignment is to focus
the enlarging lens with a negative in the holder, then
remove the negative and examine the uniformity of the
illumination on the baseboard. The enlarging lens should be
stopped down enough to eliminate mechanical vignetting from
the lens mount, usually two stops is enough. The condenser
focus can then be varied to get the best center to corner
uniformity. The D5v allows continuous focus so its not hard
to find the right setting. Any lack of symmetry in the
illumination indicates that the optical system is out of
alignment. On Omega enlargers alignment is fairly
straightforward. I found on mine that once set it stays in
alignment pretty well. I bought mine used and suspect it had
never been adjusted since leaving the factory.
Beside the problems with variable contrast paper I
found that the cold light did not deliver enough intensity
for 35mm negatives. While the brightness of the diffuser is
constant one is using much greater magnification for small
negatives so the baseboard intensity can become quite dim.
Between that and the loss due to the density of the
anti-light-piping pigment in 35mm B&W negative support, the
exposure times for large prints were quite long. Since the
condenser concentrates the light at the lens this is
alleviated although the magnification still reduces the
illumination.
This is more than I intended to write. Try printing on
VC paper and experiment with the paper grades, I am pretty
sure you will be able to get satisfactory prints.


--
--
Richard Knoppow
Los Angeles, CA, USA



 




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