DIY Robotic Scanner Back?

[maxr]

If I'm going to do it, all I really need is a large format lens, of which I have 3. I also have an enlarger lens, not worth much, I could probably test with. I'd then just build a crude box/bellows thing.

Does that sound right to you?

My big problem is a robotic X/Y axis camera mover. There are plenty of kits/ideas in the CNC world, but I want to make something cheap that you, or anyone could build.

What I've done with my panobots is use counter-weights to make the camera virtually weightless. In that way, cheap servos can move it up/down, left/right.

1. I get/build an open-end box that will take a large-format lens in the front.
2. I build a sliding open-end box for the camera movement plane on the back.
3. I build an X/Y camera mover that will take X number of images from the front lens projection.

I may not need a large sensor. The 4/3rds are after better clarity and depth of field, but for what you're doing you don't really care if you're getting 100 images from a small sensor or 20 from a large one, do you?

BTW, I will probably use a Sigma SD14, which has a large sensor and, I believe, has the most color accurate sensor available.

Any thoughts on this plan? THANKS for all your insight so far!

[Greg Lockrey]

Basically you have the idea... Large format lens to give you covering area for sure. The Sigma 14 is a DSLR, which means the mirror box will get in the way at about 6-8 exposures verses 50 with a sensor with no mirror in the way. Big sensor or small doesn't make any difference just as long as you can get the mega pixels for the area your working in. 575 mp in a 4x4" area is pretty decent. Most color fidelity can be corrected in PS. You won't beat a Sinar P rear standard for stability and would be the easiest to adapt to stepping and/or syncro motors. Everything you need to make is already there. The next thing is to hook up your camera to a bag bellows and to the Sinar frame. All kinds of adapters are out there and can be engineered to work. Sinar parts on the used market are dirt cheap compared to buying new. My set up cost about $2,000.00 to make and that was $600 for the Sinar F with P rear standard and other parts, The lens was $700... but it is top of the line Macro and the E-P1 can be had for under $300. The Studio Tool was $400... which is a lot for a bellows and hardware but considering the hassles it eliminated in camera movement it paid for itself.

[engl]

Sigma cameras with Foveon sensors have rather poor color accuracy, I'd avoid using them for this application. Reds are all over the place, as a result of being at the bottom of the sensor stack. The layered design has inherent color metamerism issues that can not be corrected.

They do however have comparatively high resolution in single-color areas compared to Bayer array cameras. They also do not have an anti-aliasing filter. They create false detail (as any sampling without filtering will do), but unlike sensors with Bayer arrays do not create "color moiré".

My guess is that the best camera to use is something like a Panasonic GH2, G3 or GF2, all with ~16 megapixels and rather weak AA filters (which is good, since diffraction will work as a AA filter anyway when using LF lenses).

[maxr]

Thanks Engl, the Sigma camera lost me at "the mirror will go back in 30 seconds no matter what you do." The challenge here, I take it, is a precise X/Y movement mechanism. The sensor will be the least of my problems if I take this on. Right now I'm leaning towards a cheap webcam, which is easy to move and control through the PC. Obviously, I'd love to go out and buy tons of equipment but like many people here, I'd imagine, I reached my marriage limit a while ago! Another possibility is any Canon that can be hacked through CHDK. I have a lens-dead G5, but I don't think it will take a photo with an error displayed. Something to research. If the webcam works, the Agent V webcam uses a CCD instead of CMOS. I have one. Going to check how easy to take apart. If you have any cheap sensor ideas I'd love to hear it.

[boris]

a short movie: http://www.youtube.com/watch?v=RkdP5...eature=related
and a forum: http://www.kolor.com/forum/f20-merli...pywizard?id=20
i use this system with good results. total cost without dslr are around 400€. in about 10 minutes you can scan the scene with 300 megapixel.
boris

[engl]

I'm not sure, but I think there is a risk a small sensor (from a compact or web camera or such) will have strange color artifacts when used far from the center of the frame, especially if using a wide lens. Sensors have a limit to the incident angle before the rays start going through one color filter and hitting the sensel supposed to go with another color filter. Microlens arrays on the sensor might also have issues with high angles in incidence. This is more of a problem as pixels get smaller, since the thickness of the color filters and microlens arrays can not be arbitrarily thin.

In short, before building anything, start by making sure that the small sensor still provides an image without crazy colors when used to capture areas far from the center of the image circle. If possible, try with a wide lens.

[maxr]

Hi Boris, I'm all too familiar with pano technologies. I even built a robotic head from the ground up. I don't know if there are any benefits to scanning a large format image vs doing a non-nodal point stitch. I found this forum because I'm selling some view camera stuff for a friend and got side-tracked. Perhaps Engl can answer the benefits of large format vs stitch photography.

On the small sensor, sounds like you're saying if you're going to use a small sensor you'd probably have to scan it in a slight parabola, which is sounding complicated. I'll try to go with a large sensor then, if I succumb to the challenge.

[engl]

It might also work, it really depends on the specifics of the sensor in your web camera. Resolution is relatively low so the pixels are not as tiny as for example 16MP cell phone cameras. Butchering a web camera sounds like fun so I'd give it a try, just make sure to test it far from the center of the image circle as well as the center.

I'm not quite sure what you mean by the "benefits of large format vs. stitch photography" though. Large format used how? Film? Stitching how?

[maxr]

The pros/cons of taking 10 full-frame digital photos with a non nodal point and stitching them together vs taking a single Large Format 4x5, for example.

[Greg Lockrey]

The pros/cons of taking 10 full-frame digital photos with a non nodal point and stitching them together vs taking a single Large Format 4x5, for example.

Digital is faster with more work and a cleaner process.
Film is easier to take the shot but takes longer to process and is messy.