jwvincent wrote:
Thanks much. I may have some of the technology confused but here's more detail on our project. We shoot all types of documents from hand written Tax Rolls, to women's club scrapbooks, to typescripts, to 8x10 photos of groups of people. We built our own rigid stand using material from 8020.com. The unit, partially disassembled must fit in the back seat of a car for transport across Texas. Commercial stands that could handle these sizes were either not available or far beyond our budget. We're in the DFW area so 80/20 had one of their design engineers help us design the thing. All of our measurements on the stand are based our alpha and beta test prototypes constructed from wood until we got what we needed. Our working maximum image size is 46" by 26" and we've already shot some that large. The vertical riser that holds the adjustable camera diving board is 48" tall so we can get the camera and lights that far from the table top. So far the smallest images we've shot in any volume are 8" x 10". Most of our documents are in the 17" x 24" size range. We can use a scanner for small stuff. The supervisor of the Tech Lab at the Portal to Texas History told us that we needed an FX DSLR camera with at least 36 mp for OCR to work and to be sure we avoided blurring at the corners (the documents we shoot often have marginal notes that are significant to historians.) We worked through the staff at Arlington Camera and they put us in contact with Sony people who came up with the camera and lens. They also recommended that we use a mirrorless camera as it has few moving parts. So far the sample shots we've sent to the Portal lab have passed muster. We're now preparing a grant request to purchase ten of these capture sets, all to be operated by volunteers, the majority of whom are retirees. The Sony has overheated twice, so we use a small fan (not shown) to keep it cool. We tether the camera to the tablet via wifi for our operators to insure images are aligned and to release the shutter. We've learned that Sony has replaced the a7R with the a7RII at a higher price. So, do we stay with Sony or explore other options, and if so, what might they be. Also can we get away with a zoom lens and use lens correction algorithms in Photoshop to address the very slight distortion we're getting in the corners of documents?
Thanks much. I may have some of the technology con... (
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Absolutely fascinating! And it obviously makes a huge difference to know more about what you are shooting and the specifics of what you currently are using.
The 8020 T-Slot materials are just super nice to work with. And while what you are doing is necessarily as simplified as possible, 8020 can come up with almost anything you might need. Imagine, as an example... taking multiple shots of 12x18 segments of a document is at your maximum size, 26x46 (or even larger), and then stitching them together to get several times higher resolution than your camera can produce with a single image. Then imagine having a computer controlled motor driven mechanism to position the camera precisely where you want it for each shot. Maybe you will never need anything like that, but it can be done as an extension of what you are currently doing.
I do have suggestions for the "rigid stand", to make it more rigid. Don't hang the lights off the vertical riser that supports the camera. Either have two separate stands for lights, or have two additional risers attached to the left and right base arms. I would also be more likely to use a couple of inexpensive studio strobe lights, probably 120 WS units, each with a small softbox diffuser.
The stand itself could use bracing on the vertical riser, with one rod or bar on each side going from near the top down to the corner on each side. Plus you really need that vertical riser to be angled to put the top out over the center of platform where the document will be. The camera absolutely must be aligned dead on in the center, otherwise you'll get perspective distortion that you do not want.
The next thing I would do is design and build a really nice, and accurate, easel on the base with sliders that make it very easy to mechanically locate a rectangular document precisely under the camera regardless of what size it is. With a little thought this could be very light, sturdy enough to survive travel, and yet save a lot of time in use.
Also, I can't tell if you have a scale, such as a metal yard stick, attached to that vertical riser, but it should have one bolted to the back if at all possible. I'm not sure how much value there is to having more or less precision, and smoothness of adjustment, for the camera position. The one T-Slot linear bearing that I use (on a macro bench) is mounted horizontally and because it mounts a 200mm motor driven focusing rail it doesn't need to be very smooth or very precise. But what I'm thinking of is how a photo enlarger works. Larger ones (that were not motor driven) were gear driven and spring loaded to be smooth and easy to work even with a heavy light head mounted. This again comes down to just how much of a problem are you having with the existing design? Is this need for a zoom lens actually significant, or just a passing thought? Another thought is a safety mechanism to prevent the camera from ever sliding from the top to the bottom uncontrolled! That would probably at least destroy the lens.
Not much that I commented on previously about the camera and lenses means much! I didn't figure you were going that large! With large documents as a likely subject, probably the 36 MP full frame camera is better. Mirrorless due to fewer moving parts is silly. Sony is perhaps okay, but they don't have the lens selection that Nikon does. Nikon cameras use Sony sensors (and often enough get better quality from the same sensor). The one problem is that Nikon's D810 camera, with 36 MP, does not sell for anything close to $2000. You can get used D800's and today maybe even refurbed D810's for that price though. Personally, I'd go with Nikon, either the D800 or the D810.
And then we are down to lenses... and this is a bit tricky. Given the size range of your documents, and the size of your stand, the choice of 35mm focal length is essential! At your maximum distance of 48" a 35mm focal length will shoot a field of view of approximately 33x49 inches, which is just bigger than the 46" space you have. Any lens with a longer focal length just won't do the trick! It also happens that your common size of about 17x24 will work with the camera at about 2 feet above the document, which is probably a very nice working distance. But... the hitch is that there are no really good macro lenses available in a DSLR mount with a focal length of 35mm! And that is
exactly what you want because only lenses designed for macro work have the very flat field that you need!
The solution is to adapt a 35mm focal length enlarging lens to mount on the camera. You won't have Auto Focus, or even Auto Aperture! You don't need either! BH Photo has at least a couple of different 35mm lenses that range in prices from $300 to $700 each. (One warning though, enlarging lens tend to have a lot of flare if your light hits the front of the lens. Some kind of a lens hood would be nice, or just make sure the lights are behind the camera!)
If you go looking for enlarging lenses there aren't too many available at a 35mm focal length, and there are specific things to avoid. Any lens that was shipped with an enlarger is not worth having! Besler and Omega made great enlargers and shipped them with horrible lenses. None of the lenses that were inexpensive back in the days of film were any good at all. But today many of the fairly good lenses from back then can be found at great prices, except 35mm was not common. Avoid Componar and Comparon (names with 'a' in them) and look for Componon or Componon-S from Schneider. Rodenstock should be good too.