File:The American annual of photography (1912) (14579271920).jpg

Identifier: americanannualof1912newy (find matches)
Title: The American annual of photography
Year: 1912 (1910s)
Authors:
Subjects: Photography
Publisher: New York : Tennant and Ward
Contributing Library: Harold B. Lee Library
Digitizing Sponsor: Brigham Young University

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and as the picture taken by the right-hand lens is to be seen by the right eye, the print from thecomplete negative must be cut through the central division andtransposed. If the lenses on the camera are 3 inches apart,and their axis parallel, identical objects in the distanceas shown in the negative will be 3 inches apart, but nearerobjects, say in the foreground, will be wider apart, perhaps3^ inches from point to point, but when the prints are trans-posed their differences will be reversed, the foreground objectsbeing nearer together. Now we already know that whenviewing distant objects in nature we do so by practically paral-lel vision and for near objects in nature the optic axes con-verge, therefore the finished stereoscopic picture must bepresented to the observer so that the distant objects are seenby practically parallel vision and the foreground objects bythe natural convergence. If then the transposed prints aremounted at 3 inches for the distant objects the near fore- 292
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PORTRAIT. Rudolf Diihrkoop. ground objects will be probably 2j/^-inch centers and if thestereoscope be provided with lenses of the same focus asthe camera lenses with an adjustment for their separation,they not only bring the picture within the range of vision, butthey enable us to use them as prisms, and thus to see the dis-tant objects by parallel vision (though it has been said theyare 3 inches apart on the slide) and, of course, we seethe foreground objects by convergence. Now, this is a point I wish to emphasize. However, per-fect the negative may be technically or pictorially, if theprint is not correctly presented to the observer the whole thingis generally a failure. When paper slides are made, theprints should be trimmed to show a little more subject onthe left-hand side of the right-hand picture than is shownon the corresponding left-hand side of the left-hand picture,but as this may seem a little confusing and perhaps not easyto remember, we will put it in another way: Let

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