Work in Progress - Blue/Green LED Enlarger Head

Discussion in 'Darkroom Equipment' started by rmann, Apr 26, 2006.

  1. rmann

    rmann Subscriber

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    I am tinkering with a Blue/Green LED enlarger head, thought I would share my progress as this has been discussed here a couple of times. I first started thinking about doing this after reading Huw Finney's article on his project, and other posts about using LEDs. What pushed me to start on this was getting a De Vere chassis without a head.

    I have an array up and running enough to do a couple of quick tests to see if I am on the right track. The first results look pretty good.


    For blue - I am using 12 - 1 watt Luxeon Royal Blue LEDs.
    For green - I am using 18 - 1 watt Luxeon Green LEDs.

    I am using an LED driver that has a dimming feature built in (LuxDrive - BuckPuck). I am planning on full manual control with no computer chips, just switches with light level control by varying the resistance.

    The test sheets are on Ilford MGRC 8x10 using a 2 1/4 negative step wedge and a 135mm lens. As the head still has a number of light leaks there was some fogging - on the left side of the test sheets. This was more noticeable with green than the blue tests.

    The Blue test was at f16 for 7 sec - I can see tones from zone 3 to 12.
    The Green test was at f11 for 7 sec - I can seen tones from zone 2 to 17
    The split test was at f11 - 3.5 sec Blue and 3.5 sec Green - I can see tones from zone 2 to 17.

    Some observations from what I have done so far -

    The head is going to be bright - about 2 or 3 stops faster than my current cold head. The paper reacts faster to blue than green. Both blue and green together have a cool white look, I do not think I will add any red LEDs as the image is bright and easy to focus. A swing away red filter should be just fine for the few times I would need red light.

    The head runs cool - the LEDs are mounted on an aluminum plate with no heat sinks for fans so far - after 10 minutes the temperature rise inside the head was from 72 to a constant 115 degrees.

    The layout of the LEDs for an even light distribution took a number of tries - I finally settled on an arrangement very close to what Huw did in his head article. I am using an old piece of fused opal glass as a diffuser, it is about 3.5 inches below the LEDs. I used the lambertain LEDs which have a narrow focused beam, rather than the batwing design. My only reason was they were cheaper. Perhaps the batwing design would allow for a shorter distance between the LEDs and the opal glass. I lined the light box with mirror scraps - it is about 7" x 9" so there is good even coverage for a 4" x 5" negative.

    I now need to finish up the switching controls - I will probably use a rotary switch and resistors for setting constant light levels at a number of different settings. Also, I need to close up the seams where there are light leaks.
     

    Attached Files:

  2. Peter De Smidt

    Peter De Smidt Member

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    Interesting work! Please keep us posted.
     
  3. Donald Miller

    Donald Miller Member

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    I agree with Peter...good work and I look forward to developments as they are completed. Thanks for posting.
     
  4. wildbill

    wildbill Member

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    good luck with the project. If you need heavier diffusion you should try Rosco or Lee sheets from expendables supply houses or wherever movie equipment is rented. There's opal, 251,250, and 216 being the heaviest.
    Led technology is becoming a bigger and bigger part of lighting as well. There are a few led lights we use. Lite panels makes a very small source that we use for shooting car interiors. Check it out. The 12x12 would make a nice 8x10 enlarging source but very expensive.
    http://litepanels.com/

    vinny
     
  5. Donald Qualls

    Donald Qualls Member

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    I'm curious -- what did the 30 LEDs cost for this? And how much additional went into the power supply? I have a D2, currently with Zone VI cold light, that might be a good candidate for this kind of conversion.

    Given the non-linearity of resistive dimming of LEDs, I'd be tempted to use a chopper circuit (like a DC-motor speed control, possibly lifted from a dead cordless drill or similar) for each array to control relative brightness, or else just split print as I've been doing with under-lens filters with my cold light, using separate timers for the two colors. Chopper speed controllers can be bought as spare parts from companies that repair these cordless tools, though a trigger isn't exactly the control input I'd like to have; I'd bet I could replace the trigger with a knob, though, since the trigger itself is just a variable resistance that supplies a control voltage to the chopper.

    Have you tested the swing-away red filter? I think you'll find it gives you, not red light, but blackness -- though the light you have may look whitish in the dark (especially under safelight, which adds a yellow or red component), there is probably no emission that will pass an under-lens "safelight" type filter. In the end, you'll almost certainly wind up having to add some red LEDs if you find you need red light for any reason (though I can't offhand imagine why you would for B&W, unless you need to adjust focus after placing your paper for some reason).
     
  6. MurrayMinchin

    MurrayMinchin Membership Council Council

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    Hey, thanks for sharing what you're up to!

    Do you know if the LED's will give consistant output, or do they vary like other light sources?

    Murray