Henry, frankly -- I am unsure if it works for shooting by conventional still cameras. I know it *is* possible for line scanners with appropriate image composition algorithms built into the drivers, and that's why I asked.
Hello again, NC.
The deeper I get into this the more questions I seem to have, instead of answers. Hence there came my question to you about distortion in stitching.
Like you and most here, I have seen stitched images which were not at all "obviously stitched."
A month ago a friend of mine here showed me a large print, about 16 by 24, of a bridge and waterline shot he had made in New York City at night. It was stunning, sharp, and looked like what one would expect from a Hasselblad or maybe even a 4X5 using transparency material. To make the shot, he had put his APS-H Canon into a vertical position and shot five frames with considerable overlap, panning horizontally for each next shot. Then he stitched those together into that one breathtaking image which I saw.
Is a single shot image of entire painting otherwise free of lens FL/perspective issues that you spoke of?
Technically, I would guess maybe not. Practically, I would say "close enough" for my modest purposes.
I suppose that a flat field copy lens might "approach" such a "freedom." Something like a long enlarging lens or a macro would be my best estimation. Failing that, one could work to minimize such distortion with more ordinary optics by reducing the angle of view (using longer focal length), making the subject plane flatter (smaller part of the arc or sphere of what is in focus), and keeping that parallel with the film/sensor plane.
AFAIK no lens is free of technical limitations of one sort or another. I have read that lens designers "balance" limitations and apply corrections to arrive at a lens that best matches some purpose they have in mind. An optic optimized for one application is probably inferior in some others.
As a practical matter, if the image suits the perceived needs of its creator or the creator's client, then well enough. I doubt if any camera or lens ever gets all things exactly, perfectly right, technically. But the results may appear
perfect to a particular shooter or viewer.
A few years ago I needed to copy some portrait paintings onto 35mm film for a family related event. These were about 40 inches by 54 inches, or thereabouts.
Having no "perfect" lens in my arsenal, I chose based upon the notion that I wanted to minimize perspective distortion, and minimize non-linearity of horizontal and vertical elements. The maximum distance available to me was about twelve feet from the paintings. I selected a 105mm f2.5 for the shots. They served the purpose well enough. My greatest concern afterwards was for color fidelity and dynamic range
, not linearity, sharpness, or perspective distortion.
For those doing this, keep in mind that oil paint brush strokes can glare even if illuminated at the commonly used 45 degree angle for copy work. I had to set the lamps at about 30 degrees off of the subject plane to keep glare off of the three dimensional brush strokes while giving the needed illumination.