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Thread: DSLR Scanner: Light Sources

  1. #1
    Peter J. De Smidt's Avatar
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    DSLR Scanner: Light Sources

    DIYS (Do It Yourself Scanner—pronounced like ‘dice’)--Light Source Thread

    Frank Pertronio started this project by suggesting that someone come up with an affordable and contemporary drum scanner, as there is currently huge gap in price and quality between consumer and professional scanners. Domaz suggested using APS-C sensors and using them to take samples of the film, similar to what Gigapan does with large stitched mosaic images. This lead to talk about making a copy stand scanning system using a dslr, a light source and a movable negative stage. Both horizontal and vertical prototypes have been made, or are in the process of being made.

    The original thread has become very long and unwieldy. As a result, I’m creating some new specialized threads for future project development.

    The new build threads are:
    Camera-Supports-and-Positioning,
    Lenses,
    Negative-Stages,
    Light Sources,
    Stitching-and-Blending-of-Images,
    Cameras-and-Camera-Control-Software.
    Workflow.

    These threads are only for positive contributions to the development in the area in question. The project may not succeed, but we’re going to find that out by trying it. But we are not unkind. As the original thread showed, some people have an overpowering urge to say negative things about the project. I’ve created a thread just for this purpose. Please post your negative comments about the project here.

    I would like to thank everyone who makes, or has made, a positive contribution to this project!

    I'll be summarizing the posts from the original thread about light sources here soon.
    Last edited by Ralph Barker; 22-Jul-2012 at 13:13. Reason: sub-thread link corrections
    "No pessimist ever discovered the secret of the stars, or sailed to an uncharted land, or opened a new doorway for the human spirit." - Helen Keller
    www.peterdesmidt.com/blog

  2. #2
    Peter J. De Smidt's Avatar
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    Re: DSLR Scanner: Light Sources

    The light source can range from diffuse to a collimated point source. Nathan Potter has pointed out that the latter might allow higher resolution and contrast. Ideally, the source has a high CRI, i.e. it's as similar to standard daylight as possible, high brightness and low heat. It could be based on flash, LED, plasma, fluorescent, or incandescent source.

    My first Light Source Prototype 1 (LSP-1), a diffusion source, looks like:








    I had some trouble with evenness, and so I move on to LSP-2, which is based off of a De Vere light mixing box for a color head for a 504 enlarger.
    Unlike LSP-1, there's not a 45* panel opposite the light source. Instead, the "reflector" panel is at a much smaller incline, just enough that on the end opposite the light source the reflector comes up exactly the to the level of the opening through which the light enters the box. The idea, I expect, is to spread the light from the source over as much of the reflector as possible. The De Vere uses a profiled piece of diffusion plastic to even out the light. Instead of that, about 1 inch above the high point of the reflector sheet, I put a sheet of diffusion. Another inch up (or so) there's the final sheet of diffusion plastic. The lighted opening is bigger than before, and I've fixed everything in place, so that the whole apparatus can't shift when I attach the flash.

    Some time soon I'll add some pictures and a diagram.

    An interesting high CRI led source is: http://www.cree.com/products/modules_lmr4.asp

    Brian Miller suggested that we could take a picture of the light source without film and apply it as a differential map to the image files. This would potentially even out the response from non-perfect source.
    "No pessimist ever discovered the secret of the stars, or sailed to an uncharted land, or opened a new doorway for the human spirit." - Helen Keller
    www.peterdesmidt.com/blog

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    Peter J. De Smidt's Avatar
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    Re: DSLR Scanner: Light Sources

    "No pessimist ever discovered the secret of the stars, or sailed to an uncharted land, or opened a new doorway for the human spirit." - Helen Keller
    www.peterdesmidt.com/blog

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    Drew Wiley
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    Re: DSLR Scanner: Light Sources

    Why not just use a colorhead with its own diffusion chamber? This was done for copy work
    in days of yore. An additive head would be preferable, one with feedback circuitry to keep
    the illumination level constant. Color quality and the ability to fine-tune it would be superior
    to any conventional light source. The trickier part of this is "low heat". There are ways to
    do this, but a bit complicated. Not simply a matter of a fan. Or just project the light from
    an enlarger, thru the image onto your capture device. Or an HMI source if one of these
    turned up used at reasonable price. LED's are still pretty bad for color quality, way behind
    color matching fluorescent tubes which can be found up to CRI 98.

  5. #5
    Peter J. De Smidt's Avatar
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    Re: DSLR Scanner: Light Sources

    As you say, heat is the reason that I don't use my color heads. And in the De Vere's case (I have a De Vere and a Philips color head) vibration due to the fan would be an issue.

    Vibration and heat would be less of an issue with a horizontal configuration, ala Mr. Denney's approach.

    The LED module I linked to earlier is available in a module that has a CRI of greater than 90.
    "No pessimist ever discovered the secret of the stars, or sailed to an uncharted land, or opened a new doorway for the human spirit." - Helen Keller
    www.peterdesmidt.com/blog

  6. #6
    Drew Wiley
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    Re: DSLR Scanner: Light Sources

    I'm rather interested in how these LED and CFL sources evolve, but mainly from a print
    display standpoint, particularly since they are now required by local bldg codes in commercial applications. Not happy about that, but hopefully the display market will drive
    better color performance. Getting a lightbox to even out might require more than a diffuser.
    Multiple diffusers help but also reduce illumination as the Lambertian factor goes up, and
    also affect color temp. One secret weapon I have found is called a linear array fresnel
    (completely different animal from a conventional fresnel), which will diffuse far more evenly
    with less loss than simple frosted panels, but at greater cost.

  7. #7
    Peter J. De Smidt's Avatar
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    Re: DSLR Scanner: Light Sources

    I wasn't able to find any pictures of that type of linear array Fresnel with a brief search. Is it similar to the type of add-on diffusers that were available for something like a Vivitar 283 flash? I have a set with ones of various colors. The have a grid like array of small pyramids on them.
    "No pessimist ever discovered the secret of the stars, or sailed to an uncharted land, or opened a new doorway for the human spirit." - Helen Keller
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    Re: DSLR Scanner: Light Sources

    It would be nice for theses threads to be made 'sticky'.........

  9. #9
    Mike Anderson's Avatar
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    Re: DSLR Scanner: Light Sources

    Quote Originally Posted by jon.oman View Post
    It would be nice for theses threads to be made 'sticky'.........
    Or just a master index thread with links to the others to not take up so much room at the top.
    Mike → "Junior Liberatory Scientist"

  10. #10

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    Re: DSLR Scanner: Light Sources

    Just noticed this set of threads!
    I have a Rosco LitePad 6x6 and it is described as ~6000K with a CRI of 93. I put a 3mm sheet of "white" plastic from TapPlastics (eyeballed as "neutral") as a diffuser and got very nice uniformity of both luminance and chrominance. I don't know how to measure CRI but I do have an IT8 from Agfa from years ago - it's piece of 35mm slide (shot with a Canon 5D2 and 100 macro). With an image of only the litepad, the values of a full exposure were from 240-251 in all three channels after WB on the middle of gray wedge. See the image below. I'm sure I can build a profile out of this The whole thing sits on a XY positioner (here is an example). The litepad has a bubble level (it stays centered as the XY go through their range) and the camera a double bubble, but I've not measured anything yet.
    I have just started playing with combining exposures as per this tutorial, as an early attempt to get the shadow noise down and it works well. Just need to set up an action that reproducibly combines each pair into one before stitching them together.
    I have not finished the project but it seems on track so far, and I thought I'd share some info now. If I finish it, I will write it up a bit more.... (and maybe put the various parts in the appropriate threads)
    Larger version is here

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