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A proportional LED colour head for Durst 138/139

  1. stormpetrel
    At last, I found a moment to finish this project of LED head for a 5x7 Durst 138/139 enlarger, I have started 6 months ago.
    The design is very similar to my first home made LED head I presented here on APUG except this one is far more powerful (the first prototypes were for a 4x5 Omega enlarger).
    I was very close to finish the omega LED head project , when I found a Durst 138/139 on our local ebay.
    Those 5x7 enlargers are so rare here in NZ, I could not resit to break my piggy bank and replace the omega with this beast

    Anyway, here are the characteristics of this new head:
    * 3x independent colour channels (R,G, B)
    * Each channel is current controlled. The amount of light can be adjusted in real-time thanks to a PC software and a remote control
    * The transfer function of each channel has been linearized
    * In its current configuration, the maximum power consumption is ~85W (equivalent to a ~500W light bulb at least). I could extend it to the limit of my driver (120W). This would require me to invest in a new and big power supply but as my darkroom is quite full. I prefer to avoid this option for the moment. The head can be run at 150W with a more powerful driver (~ 900W light bulb) but this, I'm sure, won't be necessary.
    * Cold design (the LEDs are mounted on a big heat sink)

    The red channel has a maximum power consumption of 11Watt. The red light is only used as a safe light for B&W so there was no point to increase its power. It is composed of 4x high efficiency LZ1-00R200 LEDs (Uf=2.8V, If=1A, lambda=660nm, manufacturer: Led engine)

    The green channel is composed of 30x 941-XPEGRNL100D01 high efficiency LEDs (Uf=3.55V If=0.5A, 133 lumen, lambda= 520nm, manufacturer: Cree). At its full power, the green channel consumes 35W. It might be extended to 52W if necessary but actually the current is limited to 350mA per led to fit my power supply). The amount of light produce goes up to 3200 lm!

    The UV/blue channel is made of 32x unbranded UV 395nm LEDs bought on ebay. They are rated 3W but I am using them at ~1W for the moment. I suspect from the shape of the die they are EP-U4545V produced by EPILEDS but who knows. Anyway here are the EPILED UV LEDs characteristics (Uf=3.8V, If=.7A, 40lm). The actual maximum power consumption of the blue/UV channel is ~37W but I did a try at 57W and it works like a charm!

    For the full story about LED wavelength choice, drivers, please read my previous post in this group.

    Some pictures of the head:

    On the right, the light source of the Durst139, on the left my home made light source
    On the bottom left, the remote control which is connected to the driver.
    The LED head is on and we can easily see the network of green and UV/blue led.

    My DIY B&W proportional LED head for my Durst 139/138 enlarger by stormpetrel_geek_mode, on Flickr

    At full power!
    It is VERY bright indeed. The heat think and the LEDs remains at room temperature. This is very impressive as I expected more heat generated by the LED.
    It might be another story once in the enlarger head box, but this enlarger came with an air duct and a fan to cool down the krypton head light of the durst 139, so it will be very easy to evacuate the heat if necessary.

    My DIY B&W proportional LED head for my Durst 139/138 enlarger by stormpetrel_geek_mode, on Flickr

    The red channel:

    My DIY B&W proportional LED head for my Durst 139/138 enlarger by stormpetrel_geek_mode, on Flickr

    The next step will be to try the head with 5x7 enlargement. However I will have to make a lens adapter for a nikkor 210mm first as it is the only 5x7 enlarging lens I own.
    Unfortunately it is quite a big lens designed for the Devaer enlargers, and it does not fit on the Durst.
    Maybe this weekend.
  2. stormpetrel
    The title might be a bit confusing.
    This is not a RGB colour head for colour printing but a RGB head for B&W printing only.
    The LED wavelengths have been selected to optimize printing on MG paper.
    They might not be appropriate for colour printing.
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