Quoth Wikipedia: "The exposure time of the frames is likely to have varied, even if the developed negatives were later on similar glass plates. In a letter to L

Quoth Wikipedia: "The exposure time of the frames is likely to have varied, even if the developed negatives were later on similar glass plates. In a letter to Leo Tolstoy requesting a photo session, Prokudin-Gorsky described each photo as taking one to three seconds, but, when recollecting his time with Tolstoy, he described a six-second exposure on a sunny day. Blaise Agüera y Arcas estimated the exposure of a 1909 photo taken in broad daylight to have had combined exposures of over a minute, using the movement of the moon as comparison."