VGA projector as an enlager light source

Discussion in 'Darkroom Equipment' started by swilf, Apr 24, 2011.

  1. swilf

    swilf Member

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    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. Jadedoto

    Jadedoto Member

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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.
     
  3. swilf

    swilf Member

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    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.

    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. Jadedoto

    Jadedoto Member

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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?
     
  5. Steve Smith

    Steve Smith Subscriber

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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. holmburgers

    holmburgers Member

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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.
     
  7. Steve Smith

    Steve Smith Subscriber

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    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. holmburgers

    holmburgers Member

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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.
     
  9. Steve Smith

    Steve Smith Subscriber

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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. E76

    E76 Member

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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/
     
  11. swilf

    swilf Member

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    Most probably, I will not be able to get really deep blue from an LCD projector, and a DLP-based projector should be better in respect to purity of color. Anyway, there is little need in extreme paper grades, at least in my practice.

    Vignetting seems to be another serious problem. In a normal enlarger we have somewhat abundant source of light. The limited rectangle of light from my digital mask will get darker towards its corners. There are two solutions for the problem:
    1. Digital. I can print a clear negative, scan the print and use it as a mask in PS.
    2. Analog. I can expose a piece of T-MAX, develop and use it on top of my negative carrier just like a center filter.
     
  12. Steve Smith

    Steve Smith Subscriber

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    That's exactly what I found with my LED enlarger. Grade 3.5 or possibly 4 was the most I could get.

    I think this is a good thing as if I need to go to grade 5 then I am not exposing properly or developing properly.


    Steve.
     
  13. swilf

    swilf Member

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    This sounds true regarding full frame. But sometimes it is necessary to print small part of the image with extreme contrast. A possible solution is to expose this part of the image with blue (or magenta) light filtered further through blue or magenta filter. Maybe I should always use light magenta filter in order to cut out some green from blue and get something like 1.5...4 instead of 1...3.5.
     
  14. Bill Burk

    Bill Burk Subscriber

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    I imagine a diffusion type enlarger, where you project onto a translucent sheet above the negative.

    When you go to solve the close-focus problem, you might find that you still have to crop. Cropping might solve your light fall-off at the edges.
     
  15. swilf

    swilf Member

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    I must admit that I do not have deep knowledge of optics, but it seems to me that focusing the projected image close to the negative plane is enough for the job. Sharp focusing, of course, is the thing to avoid here.

    Some cropping is tolerable as long as resolution of mask remains decent: say, 500x400 or so. Light fall-off still seems to be unaviodable.
     
  16. swilf

    swilf Member

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    By the way, most projectors now use DLP instead of LCD. In short, white light is reflected from the matrix of micromirrors and then projected through rapidly rotating color wheel:

    http://en.wikipedia.org/wiki/File:I..._DLP_-_4-segment_color_wheel_-_Green_Blue.JPG

    It seems easy to attach a piece of 00 grade yellow gel filter to the surface of green sector and a piece of 5 grade magenta filter to the blue one. And to add some balance to the red sector to avoid vibrations.