Making a Cold Light

Discussion in 'Enlarging' started by Dave Wooten, Oct 28, 2005.

  1. Dave Wooten

    Dave Wooten Subscriber

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    Specific color temp. recommended if one was to construct a large cold light head...any off the shelf bulb suggestions? straight tube bent tube curled tube etc....?

    thanks again all!
     
  2. David A. Goldfarb

    David A. Goldfarb Moderator Staff Member Moderator

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    14x17" isn't big enough? I've seen things made from straight tubes, if that's what you're thinking, though I think the ones from Aristo are made with long custom curved tubes.

    Well, whatever you decide on, you might look and see how the heater circuit works in the newer cold light heads. One downside of cold light is that the bulbs have a ramp up time that makes it difficult to get consistent output without something like a compensating timer (Metrolux) that reads the output and adjusts the time accordingly. The current style Aristo heads have a heater in them that keep the bulbs warmed up between exposures for much more consistent results without a Metrolux.
     
  3. Dave Wooten

    Dave Wooten Subscriber

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    thanks,

    confession, some of my street project stuff is done on "small format 5 x 7" and the 7 x 17.5 cameras I am testing...these will be enlarged to minimum 16 x 20 etc.....so I have recently "raided" e bay and added to my omega enlarger stash. D 2, D 2V, E5 omegalite-(bulb burned out need to find replacement...hopefully off the shelf) E5 condensor, B8 condenser, 2 B3 and 2 B22...also a "retro elwood 5 x 7--love that shape-being repainted possibly in psycho colors....and a lovely bessler 45 left out in the street for the taking.thus the question for off the shelf bulbs and also to construct a larger enlarger am looking at using the columns from an omega or bessler 45m to hold a lite for 2 x enlargement of the 7 x 17.....possibly this will have to be on a horizontal track but dont think so at 2 x etc....

    the enlargers are intended for near future use in planned analog teaching lab.

    Can you believe a perfect E5 enlarger with lenses, table and neg carriers for 66 bucks.....I just love this digital fad.
     
  4. Mike-D

    Mike-D Member

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    I've used a "deluxe warm white" which is nearly 3200k with a high CRI. CRI or color rendering index sort of measures how close the lamp comes to continuous spectrum. Cheaper lamps have spikes at certain color frequencies.

    Not sure how much that matters, but that lamp worked well with VC filters.

    Mike D
     
  5. L Gebhardt

    L Gebhardt Subscriber

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    Why not try making a VC head out of LEDs? They are very bright and use little power. An array of blue and green LEDs would make a good VC head. I have seen some plans on the net in the past and they looked simple enough to make. I am thinking of making a 5x7 head this way.
     
  6. jimgalli

    jimgalli Subscriber

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    Dave, As above, some of the stuff they're doing with LED's is fascinating but I'm completely ignorant. Hey, how many $15 Costco flashlights could it take? Wonder how the LED's would do as UV for the Pl / Pt's?
     
  7. Mark Fisher

    Mark Fisher Subscriber

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    FYI - you can get ultra bright LEDs from places like digikey.com for about $2.50 each in blue and green. If you can adjust the voltage to the LEDs, then you have a VC head. There is someone who hooked up an LED head to a RH analyzer: www.huws.org.uk It is on my list of things to do (I have a long list!)
     
  8. Donald Miller

    Donald Miller Member

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    I have used 395 nm UV LEDs in an attempt to expose Azo. My attempt was unsuccessful even when the LEDs were immediately adjacent to each other. Pt-pd would be even more problematic.

    The UV LEDs do not emit enough light even though the emission is in the appropriate band.
     
  9. Donald Miller

    Donald Miller Member

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    It's not a matter of adjusting voltage, since the LEDs require a specific voltage to operate, but rather having a circuit to switch them in and out of the circuit.
     
  10. Donald Miller

    Donald Miller Member

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    A lot depends on what you are wanting to print on. If you were printing on graded material a F15t8BLB would give you very short printing times. It may also work on Azo...the problem is that this is a black light bulb with high UVA output.

    For VC and graded materials using VC filters I would lean towards a F15T8DSGN50 which has a color temp of 5000 Kelvin.

    Both of these bulbs are off the shelf items at Bulbman. They should be able to fix you up with the correct ballasts for these too. These lamps are about 18 inches long and you could lay them side by side and six should give you the width that you need for your 7 inch negative width.

    I would plan on six lamps and three ballasts.

    The other thing is what someone already mentioned. That is that these lamps will drift as they warm up. The answer is to use a light integrator or a Metrolux timer. The other thing that could be done is to incorporate a shutter into the enlarger design. A Packard should work if you pull the pneumatic actuator and replace it with a low voltage (24VAC) electrical solonoid (available at WW Grainger and Johnstone Supply). Doing that you could leave the lamps on continually while printing and have your timer switch the solonoid and the shutter. A switching relay circuit would need to be built...but that is not rocket science.

    If you decide to go the shutter route it would require a 24 VAC solonoid, 115V-24VAC 100 VA transformer, a double pole single throw relay with 115VAC coil voltage, an enclosure, SJ 14/3 cord and grounded plug.

    Good luck...sounds like fun.
     
  11. Nick Zentena

    Nick Zentena Member

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    I had planned to do this but have been side tracked for the moment. My thoughts:

    1) Use a bunch of bulbs not one. I think T5? Home Depot had some that were pretty thin.

    2) Add a shutter of some sort. I was just planning on manual timing.

    3) Forget the warm bulbs. Look for at least daylight. 5500K or maybe the cool white bulbs. I think the 5500K bulbs will be more efficient then the warm bulbs. At least for VC paper.
     
  12. Nick Zentena

    Nick Zentena Member

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    T5 are the long ones-( I should have said T12 I think.
     
  13. Nick Zentena

    Nick Zentena Member

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  14. Loose Gravel

    Loose Gravel Member

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    Why not just have Aristo make it for you?

    With that out of the way, I would stay away from LEDs. At this size, there would be so many of them, even as cheap as they may seem, it would be expensive. And their colors may not be exactly what you want, especially if you want UV or even high power violet. LED light is so locally intense that much diffusion would be required and this amounts to severe attentuation. It might be the best light source on the planet, but the risk is high. LEDs have been around a long time and trying to buy even a small one is difficult and expensive.

    If you must work with LEDs, they are current devices. Their intensity is fairly linear with current. The other way to control their apparent intensity would be pulse width modulation: turning the LEDs on and off very rapidly.

    For coldlights, various tubes will work. If you use a Metrolux or similar, a heater may not be required if you darkroom is not freezing all the time. You can always warm the tubes by turning them on for a bit. Beware that cold cathode tubes do increase intensity with increasing temperature and then at some temperature actually decrease their output intensity with temperature. Thus the use of a heater, but it is not perfect whereas a light integrator can make the exposure perfect.

    I don't know if the newer coldlights from Aristo use a different heating system than mine, but the one I have, that isn't that old, uses a bank of resistors (the gold ones) bolted to the top of the metal chamber where the tube is. These resistors are in series with a simple thermistat that controls the temperature to about 90F.

    If you don't want to use a Metrolux, then I think you'd have to have a heater controller with a fan. The temperature would have to be accurately and evenly controlled to the peak intensity output of the tube, as this is where the output is least sensitive to temperature.

    Lots to think about. Good luck.
     
  15. Peter De Smidt

    Peter De Smidt Member

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    The daylight bulbs print about 1 stop faster than standard bulbs through a blue (high contrast) filter.

    -Peter