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  1. #11

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    Eugene, see if the manufacturer gives the range of color wavelengths for the 3 watt RGB LED. The small blue LEDs I used (at 470nm) weren't, well, blue enough. The RGB LEDs I used also didn't go far enough into the spectrum to work well.

    Sounds pretty neat refitting a old color enlarger. You'll lose a lot of light intensity bouncing around in a dichroic mixing box--this is a complete guess, but I'd say you'll need several of the big RGB LEDs in the mixing chamber to match the original halogen bulb.

    ic-racer, yes, I deliberately made the grid bigger than the 4x5 frame as I knew the corners wouldn't be as bright as the middle. The grid I built is six inches square illuminated, and it's cropped in slightly from that by the bottom portion of the box/housing that holds it all.

  2. #12

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    i just use an old crown graphic, a graflarger and a copy stand... pretty much the same concept with less diy

  3. #13

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    Hey konakoa
    I like the LED thing !
    but Beseler made a 45H it was about the same frame as a 23C II XL
    but it has a 4x5 Condenser Head !
    I have one & then made one with a Cold head
    1banjo

  4. #14
    cmo
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    Building an LED enlarger head is an interesting project. My enlarger, an Agfa Varioscope 60, is a great machine like a Focomat II, but it was was a bargain because it has a condensor head and no filter drawer. This series is high on the list of very good enlargers that could become the best choice for variable contrast papers.

    Below the line, how much would it cost to build such a head? How much time is needed to build it?

    I also saw this project:

    http://www.huwswebthing.talktalk.net/leden.htm

    Combining an LED head with an analyer/lightmeter timer is a logical step towards a homemade Heiland Splitgrade...
    The future belongs to the few of us still willing to get our hands smell like fixing bath.

  5. #15

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    Thank you konakoa for encouragement!

    An update - I finally received the 3W RGB leds. By running two of them into the mixing chamber of Beseler 67s I get about 1.5 stop less light than the halogen. Not perfect, but it should be usable for initial testing. I'm now in the process of building an f-timer with R/G/B controls...

  6. #16

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    Very nice work. I have been wondering how one might do this sort of project.

    One (of many) things that have slowed me down from considering doing a similar project (i.e. LED conversion) is that data there is no data on how contrast grade varies with wavelength. This would require a lot of experimentation to unravel, as you are finding out.

  7. #17
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    Quote Originally Posted by alanrockwood View Post
    One (of many) things that have slowed me down from considering doing a similar project (i.e. LED conversion) is that data there is no data on how contrast grade varies with wavelength. This would require a lot of experimentation to unravel, as you are finding out.
    I have decided that I don't need to know what grade someone has assigned to a particular contrast response. I just need to know that I can increase or decrease it.


    Steve.
    "People who say things won't work are a dime a dozen. People who figure out how to make things work are worth a fortune" - Dave Rat.

  8. #18

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    Quote Originally Posted by Steve Smith View Post
    I have decided that I don't need to know what grade someone has assigned to a particular contrast response. I just need to know that I can increase or decrease it.


    Steve.

    However, it would be nice to know which wavelengths produce maximum contrast, which produce minimum contrast, and which wavelengths produce little or no paper response. This information would help in choosing which LEDs to use for designing the LED array.

  9. #19
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    Yes, getting a single test-LED to evenly illuminate a 21-step wedge may not be so easy.

  10. #20

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    Quote Originally Posted by ic-racer View Post
    From the looks of it, the blue LED puts out too much green. The UV LED puts out no green, that it why it works better.
    I've been curious about what you had said, so I went about trying to find out. What I did was build a home-made spectroscope and I sampled several light sources. I went a bit more in depth here: www.deadbread.com/crumbs/spectro.html You were spot-on Ic-racer, there was some green hidden inside the blue LED spectrum. No green in the ultraviolet LEDs; yet there was bit of blue.

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