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Thread: DSLR Scanner: Camera Supports and Positioning

  1. #1
    Peter J. De Smidt's Avatar
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    DSLR Scanner: Camera Supports and Positioning

    DIYS (Do It Yourself Scanner—pronounced like ‘dice’)--Camera Supports and Positioning 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 camera supports and positions here soon.
    “If I could say it in words there would be no reason to paint.”- Edward Hopper
    www.peterdesmidt.com/blog

  2. #2

    Re: DSLR Scanner: Camera Supports and Positioning

    I'll be summarizing the posts from the original thread about camera supports and positions here soon.[/QUOTE]

    sketch I used to build from:
    Click image for larger version. 

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    the relationship between film and camera back (as if you didn't know) is the key to success. My experience is not to sweat the "micron" accuracy. Just using eyeball and "focus peaking" beats mosts scanners commonly used. Nope, not Lenny et.al. (who the hell is that guy al, anyway?)

    keep the system consistent. I used small spots of Lith pinholes at "stop" points along the travel path of the XY frame.

    Accuracy is of two types: one that costs much money, the other that costs much time.

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    Re: DSLR Scanner: Camera Supports and Positioning

    The reason for precision in the movements of the negative and the position of the camera is two-fold:

    1.) to prevent, to the extent possible, geometric distortion (i.e., perspective convergence) that will require a lossy correction during stitching.

    2.) to maintain accurate focus at the optimal aperture across the entire length and width of the negative as it is moved. Consider that the optimal aperture might be f/5.6, where there will be very little depth of field. If the film is 1mm closer to the camera at one extreme of its movement, you'll have to refocus each image before stitching. And refocusing almost always changes the magnification slightly, leading to other broad corrections that have to be made during stitching.

    It's worth some effort to build the system as accurately as possible. Micron accuracy may be unattainable, but the further we are from fulfilling that requirement, the more we will have to correct during stitching.

    Rick "hoping to finish up the negative stage and camera mount this weekend" Denney

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    Re: DSLR Scanner: Camera Supports and Positioning

    I agree with Rick. A principal reason for accuracy between stage and lens is to avoid the necessity for refocusing as one scans across the film. This will limit the distortions that need to be corrected during stitching. Note the criteria below for depth of focus vs f/no.

    f/4 = 56 mils
    f/5.6 = 78 mils
    f/8 = 112 mils

    Micron control isn't really needed but a few mils is far from trivial over 6 inches and formidable over an 8 X 10 sheet.
    The stage should have some precision leveling screws, preferably with a pitch that will allow a couple of mils of rise over half a turn. A 40 thread per inch machine screw will give 25 mils per turn, which should be adequate. Maybe check focus with lens wide open then stop down to critical aperture.

    Nate Potter, Austin TX

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    Peter J. De Smidt's Avatar
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    Re: DSLR Scanner: Camera Supports and Positioning

    Changing topics a bit, I've got some P99 1/4" thick acrylic on the way for some negative carriers. The carrier will slide on the glass plate on HDPE feet attached to the P99 acrylic. This acrylic has a fine texture to avoid Newton's rings on the base side of the negative. The negative sits base side down on the acrylic. On top of this will be an ABS hold down sheet with a cut out for the negative. There will be some pins for negative alignment. Since we want to avoid negative movement during the process, there should probably be a little force holding the negative in place. This is especially true for roll negatives, as many people have those in strips of 2 to 6 exposures. Thus, unless we build a big carrier, some of the strip will overhang the carrier, just as it does in most enlargers. (Am I right that people will not want to cut down their strips of negatives?)

    One idea is to have two (or so) threaded studs coming up out of the acrylic, such that when a knob is lightly tightened, the acrylic and abs sheets, with the negative in the middle, are pressed together. Another idea is to have a hinged carrier with magnetic closure. A third idea is to tape the negative in place and only use the ABS sheet as a mask.

    Wet-mounting would be no problem, but then I'd make the carrier out of glass. I may test this way down the road, as I really don't want to wet-mount unless I have to. I dislike covering my negatives in stuff that needs to be cleaned off.
    “If I could say it in words there would be no reason to paint.”- Edward Hopper
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    Re: DSLR Scanner: Camera Supports and Positioning

    Here is my final assembly, for the camera mount and negative stage. Given that the light source will be a standalone device, construction is now complete.

    Click image for larger version. 

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    The camera stage, from top to bottom, is the camera, with a Really Right Stuff L-plate, clamped into a Sunwayphoto macro rail, which is clamped into a Wimberley Arca-style clamp, which is bolted to a square tube that adapts it to the top of a Velmex slide with 40-turns/inch adjuster, which is bolted to a generic Sinar lens board, which rides on Incra miter-slot guides made for precision wood-working, and held down with four thumbscrew clamps. The Incra guides are screwed to the surface of the bed, which is 3/4" phenolic resin coated tool-bed plywood, which is bolted down to a 1-1/2" granite sink cutout. I added a self-adhesive tape measure to make it easier to remember general positions for each lens. It is in the correct position in these pictures for the Canon 50/2.5 Compact Macro with Life-Size Converter, which is what is installed on the camera.

    The whole mounting is quite stiff, but it has no damping and I can feel it ring at about 20 or 25 Hz when I tap the top of the lens hard. I don't feel any movement when the shutter is fired, but I think I'll need a shutter speed 10 times that ring frequency to detune it. That means a shutter speed of at least 1/250 of a second. I'm going to try a slide projector as the light source, so that should allow quite fast shutter speeds.

    Click image for larger version. 

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    I also have a bellows arrangement that can be installed on the Arca clamp and slide, too. The Incra tracks provide the range to focus the 50 that is pictured, and also a 135mm lens on the bellows.

    When loosened, there is a small amount of play in the Incra tracks--maybe 30 or 40 thousandths. I can align the edge of the Sinar board to the Incra track before tightening the thumbscrews down, however, and achieve alignment within a few thousandths.

    The negative stage is build on two precision angles designed for precision joinery in woodworking. The angles are surface-ground for precision within 0.002 over their length, but these are more accurate than that. The lateral movement runs on two IDO linear way slides (LWL9) that are 14" long, providing enough lateral motion to cover the 5" film width. These are precision ball-bearing slides, and are built around an interference fit and provide no play at all. I spent half an hour aligning the two tracks so that the motion would not bind--the two had to be parallel within a few thousandths over their length. These are 0.002" out of parallel at worst, based on measurement.

    The vertical motion is on another pair of the same slides, to which I have attached an Omega D2 4x5 holder. It's glassless, but I'm hoping the vertical arrangement will keep the film flat and prevent the issues of using glass. In this picture, a clear plastic 6" ruler is in place of the negative. I've checked the full range of motion, and there is no change in focus over that range. A film test will be more demanding, of course. But there is no wiggle in this apparatus.

    The stage is held in place using clips--accuracy in lateral positioning is not required. The mounting holes in the tracks are 20mm apart--a useful dimension. I will also attach the clear metric ruler for the horizontal movement.

    Click image for larger version. 

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    Here's a picture of the base. The bolts holding the plywood to the granite are only tight enough to establish a zero clearance. I want the plywood to be able to expand and contract without trying to warp the granite (not that it would succeed even if it tried). The attachments are at three spots, and I've installed rubber feed under the attachment point, so the whole thing sits on three feet and therefore cannot rock. The feet are not at the corners, which puts the whole structure in maximum bending. They are mid-span, so to speak, so that the stage, at least, is balancd over the feet. I an convinced this will stay flat and level.

    Click image for larger version. 

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    Rick "leaving for Anchorage and will have to wait for the next steps" Denney

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    Peter J. De Smidt's Avatar
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    Re: DSLR Scanner: Camera Supports and Positioning

    It looks good, Rick.

    You might get negative movement due to it's being heated up by the strong halogen light, but the only way to know if that'll be a problem will be to try it. Hopefully, it'll be a non-issue.
    “If I could say it in words there would be no reason to paint.”- Edward Hopper
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    Re: DSLR Scanner: Camera Supports and Positioning

    Quote Originally Posted by Peter J. De Smidt View Post
    It looks good, Rick.

    You might get negative movement due to it's being heated up by the strong halogen light, but the only way to know if that'll be a problem will be to try it. Hopefully, it'll be a non-issue.
    I considered that, but I don't think so. I can back that projector up pretty far if needed. Most of the heat gets blown out the back. As you say, we'll see.

    Rick "who needs to dig that projector out of storage" Denney

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    pramm
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    Re: DSLR Scanner: Camera Supports and Positioning

    Rick, the image you posted in the stitching thread shows that you have really made progress - and an effort! Looks like you are having fun.

    Sorry to introduce one more complexity but I see fairly major compression of the blacks in that image (hard tell from the jpeg, though). The tonal range is impaired? In that case, you need to implement a masking device that covers everything not being imaged and limits the collection angle of the lens. You may want to also put a diaphragm onto the lens itself, closing down to just outside of the active glass - sort of like a Sinar mask. These things will gain you some linearity. Working in a dark room will also help a bit, as film is actually fairly reflective and when we are looking at 1 part in 1024 (10 bits, absolute minimum for a scanning system) that becomes a factor.

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    Peter, as I keep demonstrating, I'm losing track of what even I have said. Do you mean the image of the Japanese maple? That was a stitch from a scan in a Nikon scanner. The blocked-up shadows are on the slide--it was Velvia. The Nikon did better than the Epson, though. I'd be tickled if the DSLR scanner did that well.

    Rick "who can't scan what ain't there" Denney

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