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  1. #1

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    VGA projector as an enlager light source

    I'm thinking of using an old LCD- or DLP- projector as a light source for my MF enlarger. With such a light source and a notebook one can literally paint masks for dodging, burning and local contrast contol, all in one mask that can be stored and used later. It seems to be a great tool, some blend of digital enlarger and an analog one. Resolutions of 640x480 or 800x600 seem to be enough for the purpose.

    Is it a weird idea? Can anybody suggest possible pitfalls? First of all, it would be hard to obtain extreme paper grades, but they are rarely used anyway. Second, projector lenses are designed to focus at long distances, and mask may become blurred to a degree that makes it useless.

  2. #2
    Jadedoto's Avatar
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    The nature of them, it won't block all light if you make an area black- a projector doesn't "turn off" that area of light, just filters it out more... I'm not sure you'll get the same effect as a true blocking in real dodge/burn.

    Also, how would you control time precisely? Even modern projectors are hell to get consistently on and off to any precision needed in printing... I'd see a defocused projector as a really expensive alternative to a plain lightbulb and lens... My 2cents.
    Vincent Purcell
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  3. #3

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    Quote Originally Posted by Jadedoto View Post
    The nature of them, it won't block all light if you make an area black- a projector doesn't "turn off" that area of light, just filters it out more... I'm not sure you'll get the same effect as a true blocking in real dodge/burn.
    Ok, we need "true" blocking in case of an old-style burning and dodging. With the variable light source I am thinking about all of this can be done in one exposure. You just paint grey the area you want to dodge. Or yellow. Or magenta.

    Quote Originally Posted by Jadedoto View Post
    Also, how would you control time precisely? Even modern projectors are hell to get consistently on and off to any precision needed in printing... I'd see a defocused projector as a really expensive alternative to a plain lightbulb and lens... My 2cents.
    Yes, this is the real problem. Projector lamps are inconsistent in relation to time of exposure: e.g., 20s and 10s exposures differ more than 1 Ev. Second, they are inconsistent between exposures: an already hot lamp burns brighter. One possible solution of both problems is some kind of shutter. Preheat, open, burn, close.

  4. #4
    Jadedoto's Avatar
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    You still wont get true blocking with colors... IT would most likely be putting a bayer array in an lcd or screening it in from of the dlp chip and you would still get some light leakage from unwanted spectra of light... I would test it out if you want, but since most projectors and light based systems use RGB, you will not be able to get a true enough yellow and depending on the polarizing effect of the filters used, i doubt the crystals will turn enough to block other light you dont want... Ever notice how a black image projected is never really black on a digital projector?
    Vincent Purcell
    Lexington KY Photographer + Media Artist
    http://vincenttpurcell.com

  5. #5
    Steve Smith's Avatar
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    There is only one way to find out - Ignore everyone who says it won't work and try it.

    I have successfully converted an enlarger to an LED head. With normal LEDs you do not get a full grade 0 to grade 5 range. Mine is closer to grade 1 to grade 3.5. I suspect that you will get similar results with the LCD backlight.

    I think you will need to diffuse it quite a bit to blur the red, green and blue together.

    As for selective masking - why not. In Ansel Adams' book The Print, he shows his enlarger with a 64 bulb source which had a switch for every bulb so he could selectively vary the light over the negative.


    Steve.

  6. #6
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    I think it's a great idea!

    To be concerned with the fact that a projector can't produce black is silly.. it's an enlarger light source! The fact that you have any control over the illumination in an area is a huge boon. It doesn't need to produce a wide range... any variability will give you control, the only question is 'how much?'.

    It's implications for masking are very enticing, as well as the VC and split-grade printing aspect.

    Figure out how much change in contrast can be affected by the light source while producing yellow & magenta, and I'd bet that it'll be more than adequate for useful effects. Coupled with typical VC filters, the effects could be very strong.

    A shutter is probably your only option if you're using the source from a projector. As for the lens not being able to focus at close distances, well, unsharp masks are still useful, and perhaps a different lens could be put in place. Alternatively, place the bayer filter (or whatever is in a digital projector) near the film plane and you actually could just use a normal light source.

    The ability to block the light in a very controlled and high-resolution manner is what's so promising about the project, not the light source per se.
    If you are the big tree, we are the small axe

  7. #7
    Steve Smith's Avatar
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    Quote Originally Posted by holmburgers View Post
    Figure out how much change in contrast can be affected by the light source while producing yellow & magenta, and I'd bet that it'll be more than adequate for useful effects. Coupled with typical VC filters, the effects could be very strong.
    I think you need to forget about yellow and magenta and see how much blue and green you can get out of it and what grades you can get with these individually.

    Yellow and magenta are just red added to green and blue respectively and the paper isn't sensitive to red.

    I don't think conventional filters would be needed, just varying proportions of blue and green.


    Steve.

  8. #8
    holmburgers's Avatar
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    Yes indeed. Point being, just see what the maximum range you can get is, which should be easy enough. You could even adapt some of the methods used by digital negative makers, like RNP arrays... http://www.inkjetnegative.com/images/RNP/rnp.htm Admittedly, I offer this idea with a sub-adequate understanding of the digital side of things.

    I thought that maybe the VC filters would get you in the ballpark, and the LCD-thingamajig could further refine it, but IDK really.
    If you are the big tree, we are the small axe

  9. #9
    Steve Smith's Avatar
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    I think it's definitely worth a go. The only problem I can think of is brightness. Exposure times might be a bit high.


    Steve.

  10. #10
    E76
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    It's definitely possible. DeVere makes an enlarger very similar to what you plan on making: http://www.de-vere.com/

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