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Compatible Cold light heads for Omega D5V
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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. |
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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
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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 |
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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
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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
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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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