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Thread: DSLR Scanner: Camera Supports and Positioning

  1. #41
    Peter De Smidt's Avatar
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    Re: DSLR Scanner: Camera Supports and Positioning

    Hi Ludvig,

    Thank you very much for posting!

    Regarding infrared, sure, I'd be happy to hear what you've come up with. It wouldn't be much use for BW, but it could be a godsend for color.

    Regarding the light situation, you're certainly right. Moving the light source would help minimize any recurring patterns. Our issue so far has been to find
    a light source that is flat, light, even, high cri, and reasonably priced. There's been a lot of development the last few years with LEDs, and hopefully
    some good options will appear fairly soon. One manufacturer we contacted plans on coming out with a high cri led mat by the end of the year. I do like flash
    for it's high cri, brightness, and short duration, but making a moving source with flash might be challenging.

    Taking pictures of just the light source to use to minimize any irregularities is certainly an option, but ideally I'd like to avoid it.

    Your laser idea to help with stitching is interesting and certainly worth investigating. Hopefully precise and repeatable positioning of the samples will
    help with stitching the mosaic with a structured panorama type setting, ala a gigapan. Another option is to increase magnification so that grain and defects
    provide enough control points.

    Moving on to mechanical motions, I've taken apart some free scanners and printers in the last few days, and you're right, they use belts and pulleys.
    In addition, they tend to use one bearing rod, as opposed to two parallel rods, with one side of the carriage sliding on a flat metal surface. While this
    method gives up some resistance to going out of alignment, it's a neat way to avoid binding.

    Since we don't need to take pictures while anything is moving, we don't really need super smoothness of motion. Hopefully the steppers will be fairly precise using whole steps.

    Daniel Moore and I have investigated countless rails, sliders, x-y systems..... Many could be made to work, but the better ones are quite pricey.
    The trick is finding something for a reasonable cost that others could easily source. It also matters
    whether we are going to go with a moving platen system, which would require very high accuracy in the z-plane, or a system that slides the carrier on a sheet of glass.

    We are planing on using an Arduino, mine should be arriving this afternoon, and thank you very much for the code. It's terrific that we have someone
    with experience using an Arduino helping out on the project.

    Regards,
    Peter
    “You often feel tired, not because you've done too much, but because you've done too little of what sparks a light in you.”
    ― Alexander Den Heijer, Nothing You Don't Already Know

  2. #42

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    Re: DSLR Scanner: Camera Supports and Positioning

    Yes LED is probably the best, but the white ones have pretty poor spectrum for color. At least positive, I have only used this on my cinefilmscanner, where all my stuff is reversal. Perhaps negatives are not so crucial I know a lot of filmscanners use LED like my coolscan. I have designed a small backlight for 35mm using a etched plastic with fresnels and diffusors sourced from a edgelit led backlight from a broken digital pictureframe. I guess you have looked into those. It could be interesting sandwiching 3 of those and use red, green and blue leds on them, and maybe infrared. Then one could dial in a pretty good spectrum i belive.

    Look here for more on mixing rgb. http://www.cine2digits.co.uk/ click lighting in the menu.

    Microstepping is nice and it actually gives you more torque on the motors in some situations. The vibrations of full step negates a lot of torque. Also it makes it a LOT quiter. 1/8 micro stepping is standard and only gives you benefits. It costs more or less the same to drive the motors like this, and you will have less problems with things, like mechanical accuracy. Also its important to use acceleration and deaccelleration so you dont miss steps and you will get more consistant backlash. The smother motion also put a lot less stress on the rig and things dont jerk out of place.

    Mmm I guess for prototyping nothing beats aluminum profiles like 8020. They also have some sliders and stuff.

    I didnt really get what you mean with moving platen and z acurracy. Do You mean focus stacking?

    For infrared the biggest problem is focus. Most lenses are not corrected into Infrared. As I see it you have two solutions, either a corrected lens(expensive) or a automated control over focus. To solve the problem with a corrected lens is best, when changing the focus there is usually some breathing or something can shift. It is very important that the infrared image matches the normal image 100% Otherwise you get a lot of problems in getting good results. Also on the infrared the backlight must be VERY flat. I used some scripts to batch sequences of images to include the infrared images as a extra channel, I could then use VUEscan and also Silverlight to remove the scratches. I also tried out some inpainting algorithms with good result. http://en.wikipedia.org/wiki/Inpainting The latest Photoshop has some new inpainting stuff, havent tried it yet but its probably very good, and PS is easy to automate.

    Ludvig

  3. #43
    Peter De Smidt's Avatar
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    Re: DSLR Scanner: Camera Supports and Positioning

    For their truewhite series, CRI 92, Cree mixes yellow and red leds. The mixing of various colored LEDs holds a lot of promise. One could even adjust the light source to minimize the orange mask on color negative film. I haven't really looked into the led backlit frames. I gave one to my wife to sit on her desk at work a few years ago, and the color shift over time has been awful.

    Thanks for the info on micro-stepping. It's very useful! My Arduino just arrived, and I should be able to do some experiments over the next few days.

    For good prices on aluminum extrusions, check out: http://us.misumi-ec.com/ They're quite a bit cheaper than 80/20.
    For a neat camera positioning system based on extrusions, check out: http://store.makerslide.com/index.ph...products_id=41

    Regarding Z accuracy, we are going to have very limited depth-of-field. Focus stacking could fix this, but at the cost of a lot of added complexity and shutter firings. So we need to keep the negative flat and parallel to the sensor to a high degree, especially as magnification increases. One way to do that is to slide a sandwhich style negative carrier on a flat surface, such as a piece of glass. This is my current system, and it's what I outlined in the sketchup files. With this system, the x-y system only deals with x-y positioning. The Z location is determined by the glass plate and the negative holder.

    With a moving platen version, the negative sits on a piece of, for example, P99 acrylic, and the entire piece of acrylic moves to cover the x-y positioning. This is similar to what happens on the Cezanne scanner, although the platen only moves in the x direction in that case. A moving has the advantage of having a large flat surface on which to place the negative, and one doesn't need to project the light source through a thick piece of glass. The downside is that any up and down (i.e. z axis) variation throughout the x-y movement of the stage could effect sharpness. This is an issue for a lot of the x-y positioning stages we've looked at.

    Here's a very rough sketch of a moving platen version:


    For example, lets consider the Proxxon stage you mentioned. It's true that it wouldn't be that hard to motorize, but we'd have to add a light stage on top, along with a negative holder. Without actually trying it, it's difficult to know how much z variation would occur over the stage's entire range of x-y motion.
    “You often feel tired, not because you've done too much, but because you've done too little of what sparks a light in you.”
    ― Alexander Den Heijer, Nothing You Don't Already Know

  4. #44

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    Re: DSLR Scanner: Camera Supports and Positioning

    Actually if z precision is of big importance a compound table is perfect. Its designed to be as square and parallel as possible over its entire movement. Usually its between 0.02 and 0.05mm on cheap tables. Proxxon is actually a very precise brand with good QC it might be even more precise. My milling table is a lot bigger and its a cheap chinese mill, its around 0.01mm, I just measured it with a very precise dial indicator, thats better than I remembered! As long as the lightfixture and filmholder is machined or built parallel to these tolerances it will not introduce more error, that is the beauty of the long precise parallel dovetails in that design.

    Also it is mass produced driving price down, its also very heavy and sturdy by design, minimizing vibration.

    How much z movement is acceptable on the fstop/lenses you are aiming for? Are you going to wet mount?

    When I have some time I will mount a camera and do some tests. What magnification on a full frame sensor are you aiming at? I have some enlarger lenses and bellows somewhere...

  5. #45
    Peter De Smidt's Avatar
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    Re: DSLR Scanner: Camera Supports and Positioning

    Ludvig,

    That's very good info. Hands on experience is very valuable.

    With large format, we have been aiming at 1:1 magnification, or perhaps a bit lower. For roll film, 2:1 or even higher could be useful. When reversed, most enlarging lenses perform very well at 4-5x and pretty good at 1-2x.

    Regarding z-movement, that's a good question. The higher performance lenses allow a larger aperture, which means less depth of field. Daniel had a figure in mind which I can't remember, but I'll find it and post it.

    I have a Velmex stage to hold my camera. It is terrific, but it'd be nice to have something that people can buy new for a non-exorbitant price. They do some up on Ebay quite regularly, though. Our goal is to come up with a set of plans that people can use to build their own scanner. As a result, I'd like to avoid really hard to find pieces.

    I look forward to seeing some of your results.

    Regarding wet-mounting, I really want to avoid it. I dislike having to clean film unless it's really necessary, due to a risk of damage, and mounting fluid, even Kami, needs to be cleaned off of the film. Moreover, wet-mounting is most beneficial for film flatness when it is used on a drum, where the tension on the cover sheet presses the film against the drum. That doesn't happen when wet-mounting on a flat surface, which I've done a fair bit of.
    “You often feel tired, not because you've done too much, but because you've done too little of what sparks a light in you.”
    ― Alexander Den Heijer, Nothing You Don't Already Know

  6. #46
    joseph
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    Re: DSLR Scanner: Camera Supports and Positioning

    Thanks for posting Ludwig-

    I too have just taken delivery of an Arduino, but can't do anything with it for a while. Timing belts do seem to be the correct way to drive the platform, so I'll be getting some of those too. I look forward to running my first hamfisted piece of code past you in the near future...

    I took a walk over the Brooklyn Bridge to NYC Resistor, a hackerspace, last Thursday evening, and got some encouragement from some of the members there, though not any specific solutions. I did outline the concepts, and there were no objections...

    One guy, Trammel, used Large Format in conjunction with a 5D, and has hacked the firmware- he reckons that he could program the camera to drive the stage, and perform the functions of an intervalometer, which sounds like fun...

  7. #47
    Peter De Smidt's Avatar
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    Re: DSLR Scanner: Camera Supports and Positioning

    I wish I had a hackerspace, or something similar, nearby, but I haven't been able to find one.

    I have used freecycle to pick up a bunch of old printers and scanners. They are full of useful things, such as stepper motors, linear bearing rods, belts....

    I'm going to solder up my motorshield today.
    “You often feel tired, not because you've done too much, but because you've done too little of what sparks a light in you.”
    ― Alexander Den Heijer, Nothing You Don't Already Know

  8. #48
    joseph
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    Re: DSLR Scanner: Camera Supports and Positioning

    Quote Originally Posted by Peter J. De Smidt View Post
    I wish I had a hackerspace, or something similar, nearby, but I haven't been able to find one.
    Brooklyn is hardly the next parish for me...
    I've heard there is a hackerspace in Dublin, I must try to find it. Good luck with your soldering-

  9. #49
    Peter De Smidt's Avatar
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    Re: DSLR Scanner: Camera Supports and Positioning

    Quote Originally Posted by ludvig friberg View Post

    How much z movement is acceptable on the fstop/lenses you are aiming for?

    .
    Our theoretical investigations are pointing to about 300 microns at 1:1 and approximately F8. At 2x things get much, much worse, with a dof of about 9 microns.
    “You often feel tired, not because you've done too much, but because you've done too little of what sparks a light in you.”
    ― Alexander Den Heijer, Nothing You Don't Already Know

  10. #50

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    Re: DSLR Scanner: Camera Supports and Positioning

    wow... thats pretty crazy!

    Just to get this straight you talking about micrometers right? so 300 microns is 0.3mm and 9 microns is 0.009mm. Is that like +- , hyperfocal? I would say that it will be VERY difficult to get that kind of accuracy, I mean the sensor need to parallell to film that tolerance, the lens to the sensor. The lens itself must be very precise. The movement needs to be parallell to that tolerance and the film sheet needs to be flat within a few microns...

    I dont know how they do it in the Nikon scanner but I can assure you it is at least +- 0.3mm and thats when its sharp! Sometimes it will be more bends and warps in the film and then things get out of focus, but then we are talking about probably 1 mm uneven.

    Would it be better to use a small sensor with tighter pached sensels or am I just confused?

    I will make some tests with my mill as a base and a 50mm el nikkor at f8 on bellows I guess I will go for 1:1 or slightly more. Do you have any suggestions on what to use for a test subject? I was thinking of printing something and glue it to a pice of aluminum machined on my mill. That will make it parallell to my test setup at least. Maybe I will just print a raster pattern with some numbers to identify and stitch, could be interesting to see how my new printer places the little drops!

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