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  1. #11

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    Nice trick with the photodiode megamahi - thanks!

    If you're going to go to all that effort anyway, why not go down the LED head route. There have been posts in the past if you're interested and I have a few ideas of my own...

  2. #12
    ic-racer's Avatar
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    Quote Originally Posted by megamahi View Post
    For the screw-in CFL bulbs, to test if its fully warmed I use a IR photodiode
    Yes, good idea. I do something similar with my coldlight. :http://www.largeformatphotography.in...4&d=1203349768

  3. #13

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    If you are worried about temperature try getting a probe meat thermometer. You can get one at the kitchen store and they are pretty cheap. You just set it to beep if it gets too hot. You may just want to turn the bulb on and leave it on for an hour or so with the probe in, see what temp it hits.

  4. #14

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    @David: I'll have to take a look at doing a LED head. I'll have to search a bit for more info on that. Not sure about how bright the LED head would have to be to work well. Any idea on the light output or spectrum output that would be needed? Any ideas are welcome.
    @Zach: Easy enough, haven't done much work on it this week as my schedule is packed, though there should be some progress this weekend.

    I was able to obtain a Beseler 23C with a 23dga, color meter, and other assorted goodies on Monday. I'm not saying that we have abandoned this project (we haven't), but I'm cleaning that up a bit and making notes as to what I see that can be easily implemented into this enlarger. Going along with David's idea, would building a LED head with many colored or RGB LEDs work for making a form of dichro head?

  5. #15
    htmlguru4242's Avatar
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    I believe CMY LEDs would be needed for a dichro head; not sure what RGB would do in that respect.


    It's a great idea, though.

  6. #16

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    Actually you'd want it to be RGB. CMY works with having a continuous spectrum and filtering parts of it out. LEDs have only a narrow emmission spectrum and thus are more suited to the additive approach.

    The Phillips Tri One enlargers used an additive system using tungsten bulbs and filters (VERY inefficient).

    You can look at the spectral sensitivity curves for the paper you use (they're all fairly similar anyway) to determine the best wavelengths.

    Sorry for the short, fragmented reply - will post more when I get home tonight or tomorrow morning...

  7. #17

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    Ok, see here for a previous thread which discusses an LED head for multigrade paper (green/blue LEDs). Just add red

    Personally I'm not sure I'd bother with a microcontroller - I'd probably try a linear variable current source first with a 10 turn potentiometer or similar and ammeters to provide a value.

  8. #18
    Steve Smith's Avatar
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    Quote Originally Posted by David Grenet View Post
    Personally I'm not sure I'd bother with a microcontroller - I'd probably try a linear variable current source first with a 10 turn potentiometer or similar and ammeters to provide a value.
    I wouldn't use a microcontroller either. And instead of a linear current source I would use a variable duty cycle switching circuit working at around 1 - 10 KHz.


    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.

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