This is an easy concept: scan a large painting like these strange, happy folks schlepping a shark that is 44” x 84” in several sections (”tiles”)and stitch them together (seamlessly with an app like Photoshop or Panotools. To do this, several requirements must be observed:
1: Light it Properly
The sections of the art to be tiled must be lit uniformly.
Uniform lighting sounds easy, if you have a good light meter, right? It can get you close, but even the best lenses have some minor transmission fall-off from center to the outside, it is necessary to use the Betterlight’s Viewfinder software can act as a “spotmeter” showing the light levels actually reflected from the art. We use a large piece of gray matte board to check. In the assembled large, we see the white areas of the three tiles matching in luminance perfectly.
2: The Lens is Critiical When Copying in Tiles
The camera lens in use must be completely free of distortion: the two most common are barrel distortion (“pincushion” or “barrel”), and chromatic aberration.
The first type, Barrel Distortion, is prevalent to a degree in all wide-angle and zoom lenses. Normal amounts of these flaws are accepted in normal “situational” photography, but in art copy, they are lethal, especially if you are trying to seamlessly stitch together adjacent tiles. Long lenses, particularly the type we use that are designed for flat-field copying in lithography, are perfectly linear.
Chromatic aberration is generally found in cheap(er) or old(er) lenses, a “rainbow” fringe distortion is particularly evident toward the edges of a photograph. and is a result of the lenses unable to resolve the spectral colors of a photograph. Today’s “apochromatic” lenses solve this problem with computer design and multiple-coatings. There are photographers around who have a pre-war Zeiss lens with the claim "They don't make them like this any more!" There is a reason why.
3:The camera must be aligned perfectly to the art.
The Zig-Align® system is an elegant, if simple way to check alignment of the Betterlight digital sensor plane, camera Lens, and art copy planes to prevent “keystoning” (i.e. a trapezoidal image) especially if the image is to be “tiled” to create a larger file. The system (shown below) consists of a square mirror hung on the easel, and another unit, exactly the same weight and shape of the Betterlight scan insert. This insert has another circular mirror facing the art with a hole in the center. When the camera is perfectly aligned, the mirrors “cascade” in a concentric display.