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  1. #11

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    Well I think a controller like the arduino should be great for a full auto exposure monster... Something with a cds cell embeded to use instead the test strips...
    A higher wavelenght Uv source should be interesting for alt processes (but will ned a UV friendly coating on the lenses ) that's just thoughts.

    The idea is great! I will try to keep following this thread...
    Réparation, Restauration d'appareils et équipements anciens, exotiques et modernes: http://www.atelierdeblanc.fr

  2. #12

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    Quote Originally Posted by Steve Smith View Post
    At the moment I just have a rotary switch with four positions: Red, green, blue and all three. I will arrange it so it works through this permanently at 100% or via the variable controller. It will need a permanently on position anyway for focusing.
    Consider focusing with green light only. That's where the human eye is most sensitive, and Patrick Gainer did some tests (published in Photo Techniques a while back) in which he found that focus via a grain focuser was best when using either green or white light. Since your "white" light is a combination of separate red, green, and blue wavelengths, it's not clear that it would be the same as "white" light from a typical enlarger bulb. FWIW, I'm in much the same situation via different technology, since I've got a Philips PCS130/PCS150, which uses a color head with red, green, and blue light produced via halogen bulbs with filters. I use green light for focusing.

  3. #13

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    If the color balance is close enough for the eye to percieve the light as "white" from the red, green, and blue LEDs, it will be good enough. Certainly better than using red alone.
    Kirk

    For up from the ashes, up from the ashes, grow the roses of success!

  4. #14

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    How possible would it be to construct a colour LED enlarger head?

    Tom

  5. #15
    Steve Smith's Avatar
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    Quote Originally Posted by Kirk Keyes View Post
    If the color balance is close enough for the eye to percieve the light as "white" from the red, green, and blue LEDs, it will be good enough. Certainly better than using red alone.
    I have been using blue and green together as they are the colours the paper is sensitive too. It's bright enough without the red.


    Steve.

  6. #16

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    Quote Originally Posted by Tom Kershaw View Post
    How possible would it be to construct a colour LED enlarger head?
    In theory, the head under discussion in this thread would work for this, depending on the exact frequencies of the red, green, and blue LEDs vs. the sensitivity of the red-, green-, and blue-sensitive layers in color paper. You could then vary the brightness of the red, green, and blue LEDs instead of adding cyan, magenta, and yellow filtration. This would work just like a Philips Tri-One (PCS130/PCS150 or PCS2000) enlarger.

    Quote Originally Posted by steve smith
    I have been using blue and green together as they are the colours the paper is sensitive too. It's bright enough without the red.
    The sensitivity of the paper isn't really important, unless your lens suffers from pretty bad chromatic aberration. (Some do, but good enlarging lenses minimize these effects.) What's important is the sensitivity and focus characteristics of the human eye. Patrick Gainer's article in the January/February 1997 issue of Photo Techniques magazine tells the story in detail, but the summary is that he got best results using either green alone or white light. I don't believe he tested the blue/green combination, but blue alone was slightly worse than green alone or white, and red alone was abysmal compared to green or white.

  7. #17
    Steve Smith's Avatar
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    Quote Originally Posted by srs5694 View Post
    but the summary is that he got best results using either green alone or white light. I don't believe he tested the blue/green combination, but blue alone was slightly worse than green alone or white, and red alone was abysmal compared to green or white.
    The fact that blue was worse than green is interesting in view of the fact that some of the grain focusing devices come with a blue filter. Perhaps a green filter would be better.


    Steve.

  8. #18

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    Quote Originally Posted by Tom Kershaw View Post
    How possible would it be to construct a colour LED enlarger head?

    Tom
    I'll let you know in a month when I complete my 'proof-of-concept' version. Fifty RGB Endor Stars, with each color on a separate PWM circuit.

    justus

  9. #19
    Nicholas Lindan's Avatar
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    These things have their own micro-controller and are meant to be controlled by computer. Some control is available from the switches on the back.

    The DMX protocol is available on the web http://en.wikipedia.org/wiki/DMX512

    DMX is designed to be used by dummies (volunteers at the community theater and that sort of thing) and will generally make sense out of anything that 'looks about right'. Some of these lights will work connected to an RS232 port - just because that's often what happens to them - along with the RS485 signaling specified.

    You can send the light a simple command to set the intensity of the three color channels as a level between 0 and 255. The lamp's micro-controller does 3 channels of PWM to control the intensity. 255 grades of paper should make most anyone happy.

    You could make rather a nice VC head/f-stop timer connecting one of these to a lap-top and doing a bit of programming. Oh, dear, cat's out of the bag...

    Google for more.
    Last edited by Nicholas Lindan; 08-12-2010 at 06:42 PM. Click to view previous post history.
    DARKROOM AUTOMATION
    f-Stop Timers - Enlarging Meters
    http://www.darkroomautomation.com/da-main.htm

  10. #20
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    Steve,

    Thanks for all of this - I had been thinking about this for some time and feel very inspired to draught up my own designs. Very innovative work and I look forward to going through your articles more thoroughly right after I make this post. Startiinnnng.....NOW!
    -dereck|james|gignac
    dereckjamesgignac.com

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