The American annual of photography . same state ofthings as originally existed with the camera. If, for in-stance, we make a second mark on the sliding extension frameone-fourth of the focal length behind the first mark, andmove the extension frame forward till the mark corresponds 217 with the edge of the base-board, the apparatus is accuratelyfocused for a four-diameter enlargement, and one need onlymove the easel, without any other adjustment, till the imageis seen to be sharply focused. A scale, also, may be pre-pared and fixed to the extension frame for obtaining enlarge-ments to any othe
The American annual of photography . same state ofthings as originally existed with the camera. If, for in-stance, we make a second mark on the sliding extension frameone-fourth of the focal length behind the first mark, andmove the extension frame forward till the mark corresponds 217 with the edge of the base-board, the apparatus is accuratelyfocused for a four-diameter enlargement, and one need onlymove the easel, without any other adjustment, till the imageis seen to be sharply focused. A scale, also, may be pre-pared and fixed to the extension frame for obtaining enlarge-ments to any other desired size, and this scale will have thesame measurements or graduations as that employed with thecamera. The only difference is that, in the first case, thesensitive surface or bromide paper is placed in front of thelens and the original or negative behind it, to get an enlarge-ment to a given ratio; while, in the second case, the distancesremain the same, but the sensitive surface, or plate, is placed . I )f^FOCAL LEA/CfTH--^. MAfiK £XT£/^SlO/V HERE Figure 4. behind the lens and the original or copy in front, which givesa reduction instead of an enlargement, though still in thesame ratio. Where we should get a four-diameter enlarge-ment we obtain a one-quarter size reduction, and so on. En-largers differ a good deal in design, and in some cases it maybe more convenient to mark the baseboard than the exten-sion. Passing from flat subjects, such as copies, to those includ-ing a number of objects at different distances, the photogra-pher is apt to get puzzled as to what factors really regulatefine definition. We hear a good deal about depth nowa-days, and the would-be purchaser of an expensive anastigmat 218
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Keywords: ., bookcentury1900, bookdecade1910, bookpublishernewyorktennantandw
