Originally Posted by
Peter Mounier
The Betterlight scan back works like a flatbed scanner, in that it scans lines across the film plane. Depending on the model, it has to scan about 8,000 lines to make one (slightly smaller) 4x5 image. Those 8,000 lines can be exposed for up to 1/8th sec. each, making for very long exposures overall, but only 1/8th sec. per line. Not only that, but each line gets exposed by a trilinear sensor, meaning that each of 3 colors gets scanned separately with each line. The scanback software stitches the 3 colors together and also the 8,000 lines in the controller box. If something is moving, the colors can become out of register, and the separate lines also won't align. Thus the need for stillness. Here is a crop from a shot I intentionally took with some motion. Each line got 1/30th sec. for an overall exposure time (1/30th x 8,000) of approx 2.5 minutes.
Peter
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