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  1. #1
    Steve Smith's Avatar
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    Results from LED Enlarger light Source

    Further to my posts on getting a large format enlarger and converting it to use an LED light source, here are some scans of some actual prints produced!

    The first is one which I'm optimistically calling 'normal' contrast uses both the blue and green LEDs on together. It does appear normal to me:



    The next print I made was with just the blue LEDs. As can be seen, the contrast is higher:



    And with only the green LEDs being used, contrast is lower:



    The negative is 5" x 4" and is one of four I took on the first trip out with my home made camera a few years ago (yes, I only owned two film holders at the time!). It is not particularly exciting but is adequate to test the enlarger out. Prints are 10" x 8" on Ilford MG IV.


    Steve.
    Last edited by Steve Smith; 07-29-2010 at 05:39 AM. Click to view previous post history.

  2. #2

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    Whow nice!

    And with less powerfull leds placed in a kind of matrix you should fine-tune the contrast?
    Réparation, Restauration d'appareils et équipements anciens, exotiques et modernes: http://www.atelierdeblanc.fr

  3. #3
    Steve Smith's Avatar
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    I can fine tune the contrast using varying ratios of blue to green on time. I have plans to make a rotary 'contrast' control which is green only at the anti-clockwise end and blue only at the clockwise end, crossing over with 50-50 in the middle using pulse width modulation.

    It could be done just as easily with separate exposures for each colour though.

    I think I am getting about grade 1 with the green LEDs and no higher than 3.5 with the blue. Whilst it would be nice to have a grade 0 to grade 5 range, having it limited a bit may make me think a bit more about getting the contrast right in the negative!

    There is a bit more information on my previous thread here: http://www.apug.org/forums/forum43/7...ad-update.html


    Steve.

  4. #4

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    Arduino controller for control?

    Steve;

    Really interesting thoughts! Thank you.

    For a timer/contrast controller, the little Arduino boards may be good for it. Program in "C"; can take a potentiometer as input (or switches, or...) and IIRC the newer boards can directly control a couple of leds using PWM outputs, just what you need for controlling the amount of light output.

    Whatever - you are doing really neat work. I have 2 older Omega condenser enlargers, and you have me thinking... (b600 and b66xl)

    JohnS,
    Ottawa.

  5. #5
    Greg Davis's Avatar
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    Since you had red LEDs in there originally, you may want to replace some with LEDs that extend higher in the blue wavelength to gain more contrast. If they are violet or near UV it may give more of a grade 5. Just a guess. More of a yellow green may also produce lower contrast.
    www.gregorytdavis.com

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  6. #6
    Steve Smith's Avatar
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    Quote Originally Posted by johnalex141r View Post
    For a timer/contrast controller, the little Arduino boards may be good for it. Program in "C"; can take a potentiometer as input (or switches, or...) and IIRC the newer boards can directly control a couple of leds using PWM outputs, just what you need for controlling the amount of light output.
    I will build the controller myself then I can have exactly what I want. Plus I don't like spending money on things I can build!!!

    Quote Originally Posted by Greg Davis View Post
    Since you had red LEDs in there originally, you may want to replace some with LEDs that extend higher in the blue wavelength to gain more contrast. If they are violet or near UV it may give more of a grade 5. Just a guess. More of a yellow green may also produce lower contrast.
    Whilst that is a good plan, I like the idea of having it limited to around 1 to 3.5 as I will then think a bit more about getting the negative right.

    The reds are wired in so I can have a safe setting for checking that the easel hasn't moved and for positioning dodge and burn masks before exposing, etc.


    Steve.

  7. #7
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    Fascinating and inspiring! Thank you Steve for posting this series of articles and sharing your findings. The preliminary(?) results looks very encouraging.

    A few questions poped into my mind so, I'm just going to blurt them out...
    What are you using for a diffuser?

    What is the distance, roughly from the LEDs to the negative? and where is the diffuser relative to the negative?

    In your previous post, you showed a photo of the LED array...is that an off the shelf item?
    any idea what the specs are for the individual LEDs?


    Thanks again!

  8. #8
    Steve Smith's Avatar
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    The LED PCB came from an LED stage light like this: http://www.matrixproductions.com.au/...LED_Par_64.jpg

    Being sold here: http://www.ledssuperbright.com/par-6...ight-rgb-p-205

    I do some live sound engineering for a local sound company and repaired a couple of their lights and got to keep a PCB from one of them.

    I have no idea what the specifications are. They are probably the cheapest and brightest the light manufacturer could get.

    The LEDs are about 5" above the negative. There is a diffuser layer near the LEDs and one just above the negative. The one above the negative is part of the original light system which used a water filled diffuser (I couldn't believe it either!). I cut out most of it leaving just the base which is a semi-translucent/milky plastic. The diffuser just below the LEDs is a few sheets of velvet textured polyester (Autotex V207) which we use at work for printing control panel/membrane switch graphics onto.

    The diffusion seems to work well as the prints appear to be evenly exposed all over. A quick, un-scientific check with a light meter showed this to be the case too.


    Steve.

  9. #9
    MattKing's Avatar
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    Steve:

    If you are looking for ideas ....

    For those who are into split grade printing, it would be very useful to have an "either/or" control. By that I mean a control that either uses the rotary control, or uses a switch that goes from full green to full blue, and gives repeatable results each time.
    Matt

    “Photography is a complex and fluid medium, and its many factors are not applied in simple sequence. Rather, the process may be likened to the art of the juggler in keeping many balls in the air at one time!”

    Ansel Adams, from the introduction to The Negative - The New Ansel Adams Photography Series / Book 2

  10. #10
    Steve Smith's Avatar
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    Quote Originally Posted by MattKing View Post
    For those who are into split grade printing, it would be very useful to have an "either/or" control.
    That's probably what I will do. 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.


    Steve.

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