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  1. #11
    Rick A's Avatar
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    All I need to add are Horizontal and Vertical Hold controls and it will resemble a 1960s TV!


    Steve.[/QUOTE]

    And your dad sitting in his favorite easy chair directing you how to adjust the thing, and "change that channel, I dont like what you're watching!"
    Rick A
    Argentum aevum

  2. #12
    greybeard's Avatar
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    All I need to add are Horizontal and Vertical Hold controls and it will resemble a 1960s TV!

    Oh, come on---this is the 21st century; you should at least come into the 1970s and add a wired remote control

  3. #13
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    Keep working on it Steve, it's a fresh breath of hope in light of the Aristo demise, I know I'm following your work with great interest. Maybe when you are ready a photo of it would be nice.
    Everytime I find a film or paper that I like, they discontinue it. - Paul Strand - Aperture monograph on Strand

  4. #14
    Steve Smith's Avatar
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    Here are the pictures I have made so far:


    Steve.
    Attached Thumbnails Attached Thumbnails DSCF0387.JPG   DSCF0388.JPG   DSCF0389.JPG   DSCF0390.JPG  
    "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.

  5. #15
    Thomas Bertilsson's Avatar
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    Well done, Steve!

    So you balance contrast by altering how many green and how many blue diodes are illuminated?

    It's great to be able to focus with green light also, because that's the color our eyes are the most sensitive to.

    Forgive my ignorance, but what are the red LEDs for?

    Thanks,

    - Thomas
    "Often moments come looking for us". - Robert Frank

    "Make good art!" - Neil Gaiman

    "...the heart and mind are the true lens of the camera". - Yousuf Karsh

  6. #16
    Worker 11811's Avatar
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    Steve,

    How handy are you with electronic circuit building?
    Can you make a pulse width modulation circuit to control the brightness of the LEDs?

    You don't want to try to vary the brightness of the LEDs with pure resistance because they are not voltage driven devices, they are current driven devices. If you try to use a potentiometer you won't get a linear response out of them. You'll drop the voltage below the forward threshold of the LED and it will just peter out on you.

    Instead, vary the length of time each LED is lit by minute amounts. Do this and you will have very precise control of the mixture of red, green and blue light emitted by your array.

    And, in turn, you might get a very interesting method of contrast control from your enlarger which is operationally similar to dialing in contrast settings on a diachronic color head.

    Here is an example of the PWM control I am talking about for LEDs.
    http://www.robotroom.com/PWM4.html
    (Just the first part at the top of the page.)
    Randy S.

    In girum imus nocte et consumimur igni.

    -----

    http://www.flickr.com/photos/randystankey/

  7. #17

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    Quote Originally Posted by Thomas Bertilsson View Post
    Forgive my ignorance, but what are the red LEDs for?
    They could be used as a safelight for aligning paper etc, like enlargers which have a red filter which can be put beneath the lens...

    How safe are they Steve? (and where can these be had inexpensively )

  8. #18
    Curt's Avatar
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    It that a 74AC14 Hex Schmitt-Trigger Inverter? Do each LED have a separate circuit or can they be group in Red, Green, Blue etc.?

    If the light is right then control is the problem to be solved. Thanks for the photos Steve.
    Everytime I find a film or paper that I like, they discontinue it. - Paul Strand - Aperture monograph on Strand

  9. #19
    BetterSense's Avatar
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    Making your own PWM circuit is a valid exercise, but LED drivers are pretty cheap and available. I bought a digitally regulated, multi-mode driver board for a homemade flashlight on Dealextreme.com for $1.63 with free shipping. So there are probably ready-to-go PWM led drivers available, especially with LED becoming more popular for household lighting.
    f/22 and be there.

  10. #20

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    (re: red LEDs)

    Quote Originally Posted by David Grenet View Post
    They could be used as a safelight for aligning paper etc, like enlargers which have a red filter which can be put beneath the lens...
    I'm not the one who designed and built it, but if they're the right color (and if the blue and green LEDs are the right color), the whole setup could be used for color printing, too. This would be conceptually very similar to a Philips Tri-One enlarger, which uses halogen bulbs behind red, green, and blue filters to provide light for VC B&W and color printing. I've got one of the Philips machines and it works quite well.

    How safe are they Steve? (and where can these be had inexpensively )
    I don't know about the LEDs that Steve used, but I've got a red LED safelight above my darkroom's wet side. It's bright, compared to other safelights I've used, and safe out to at least several minutes. (I don't recall the limits of my tests, but it was probably at least five minutes.) Of course, the intensity may be less than what would be projected by a red LED light source in an enlarger....

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