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  1. #1
    aparat's Avatar
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    Help with a cold light head

    As I am continuing to learn BW printing I decided to try a cold light head. I had a chance to get an old Aristo head for free, so I thought I'd give it a try. The head came with a power supply. It seems to emit blueish light. I mounted it on my Beseler 23c III and ran a few tests. Overall, I really like the results with Ilford Multigrade RC paper. I used a contrasty negative, without multigrade filters. The tonality was really nice, with lots of highlight and shadow detail.

    However, the light intensity is not consistent. It varies from exposure to exposure. So my question is whether there is anything that can be done about it, or should I just forget about and use my condenser head instead.

    Thanks!

  2. #2
    Ian Grant's Avatar
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    Cold heads need to warm up. I used one for about 30 years with no problems, but for critical work I'd make sure I switched it on for a few seconds, often with a piece of card shielding the paper. Taht seemed o work well.

    Ian

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    aparat's Avatar
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    Quote Originally Posted by Ian Grant View Post
    Cold heads need to warm up. I used one for about 30 years with no problems, but for critical work I'd make sure I switched it on for a few seconds, often with a piece of card shielding the paper. Taht seemed o work well.

    Ian
    Thanks, Ian. That helps. It makes perfect sense. I will try that when I have a chance.

  4. #4
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    Read about the Stop Clock Vario, a timer with a light sensor that gives consistent exposure, time after time. http://www.rhdesigns.co.uk/darkroom/...ock_vario.html
    Also if you search here on sponsor R.H. Designs and F stop timer you will find quite a lot of positive feed back. Finding one for free will be a bit more of a challenge.

    John Powers

  5. #5
    RJS
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    All my cold lights have had heaters (all are Aristo). There should be 2 cords coming from the light housing. One operates the light, the other the heater. The heater cord gets plugged into a regular switch like a light switch - off and on. On the Beseler enlarger there is a plug on the motor housing to plug into. You leave the heater on while you are printing - the light will feelquite warm. Withouht being warm the tube in the cold light does not go on immediately and tends to flicker a bit. Irregular, inconsitent exposures. With the heater mine is very consistent. Some people feel the need for a feedback sensor arrangement sold by RH Designs with their excellent timer for cold lights, but I have not found the need for one. All my tests indicate good consistency, but by all means look at the RH Designs web page for good information!

  6. #6
    aparat's Avatar
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    Quote Originally Posted by RJS View Post
    All my cold lights have had heaters (all are Aristo). There should be 2 cords coming from the light housing. One operates the light, the other the heater. The heater cord gets plugged into a regular switch like a light switch - off and on.
    Yes! I was wondering what this cord was for. Thanks so much, this is incredibly helpful, as I would have never guessed that the extra cord was for a heater.

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    No mention of a voltage stabilizer. When the lamp is cold, you cannot achieve much intensity without the source becoming unstable (goes from nice constant beam to a high-freq flickering). A voltage stabilizer also compensates for the light-up and light-down, i.e., voltage is always unstable when turning on and off. I would have to check mine, but the stabilizer is an extra box between timer and enlarger.

    The strong blue hue put off by the light must also be compensated for with VC papers. (Perhaps Arista is different, but still a fluorescent source, thus heavily blue.) This makes no difference with graded papers. A simple color correction filter, light yellow, like a Kodak YCC40 between light and diffuser will bring your unfiltered VC papers to a grade 2 or 2 1/2 (vice about grade 5 without). Of course, once you have the CC filter up top, use regular multigrade filters below for your printing. Hope this was not too convoluted an explanation. Good luck.

  8. #8
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    My coldlight has a heater. Understanding the nature of the unit allows me to easily work with it rather than against it.

    http://www.apug.org/forums/forum43/5...mperature.html

  9. #9
    aparat's Avatar
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    Quote Originally Posted by Rich Ullsmith View Post
    The strong blue hue put off by the light must also be compensated for with VC papers. (Perhaps Arista is different, but still a fluorescent source, thus heavily blue.) This makes no difference with graded papers. A simple color correction filter, light yellow, like a Kodak YCC40 between light and diffuser will bring your unfiltered VC papers to a grade 2 or 2 1/2 (vice about grade 5 without). Of course, once you have the CC filter up top, use regular multigrade filters below for your printing. Hope this was not too convoluted an explanation. Good luck.
    Thanks, that helps a lot! My Aristo head is about 5 inches in diameter. Where can I purchase a Y40 filter of this size? I suppose this could be a simple resin square filter that I could cut to fit the bottom of the cold light housing. Is that correct?
    Thanks!

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    Interesting Thread : Aristo CC heads are rare (but not completely unknown) in the UK. The CC heads I'm most familiar with are those made for DeVere 54 enlargers. I've seen some of these attached to voltage stabilisers and some not. There's no heating circuit in the DeVere heads and, although I've seen some heads fitted with timers (alwaysmade by Rayco), I always understood this to be bad practice because of the time required to reach a steady output.
    It was more common to have a simple (double pole) switch, in the line between the head and the power supply and to leave the head switched on all the time. Exposure being controlled by swinging a safelight filter into the light path.
    Exposure times tended to be long (30 secs +) and I never heard it mentioned that the output diminished as the head became hotter : Presumably we simply accepted that the head reached a steady state.
    Whether controlled by a simple switch or timer, all switching devices featured 'double pole' switching.
    Regarding the large Y40 flter, You need to find a local supplier for Rosco filters - they make filters for movie making and stage lighting - I usually get them from a shop that sells and hires 'disco' lighting kit, much more common than photo suppliers.
    Regards Jerry

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