One of the greatest difficulties the photographer, and especially the amateur has to encounter, lies in correctly estimating his exposure. Of course, by one who is in the habit of making almost daily exposures, experience is gained, which is a more or less certain guide, but by the photographer, who only occasionally exposes a plate, some better guide is required if certainty of result is to be expected. The fluctuations of the light throughout the year, and again throughout the day, are so great that we believe nobody, be he professional or amateur, can adequately allow for them unless he has some reliable data to go upon. Then, again, with the era of gelatino-bromide dry plates, a new difficulty arose in consequence of the great variety in their speeds. This is a very serious complication, and has never hitherto been scientifically dealt with, a satisfactory unit of speed never having been found.

The Actinograph, A Paper read before the Liverpool Amateur Photographic Society, 25th April, 1889

The photographic researches of Ferdinand Hurter & Vero C. Driffield (Unknown Binding) by Ferdinand Hurter

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