File:The American annual of photography (1917) (14597377180).jpg

Identifier: americanannualof1917newy (find matches)
Title: The American annual of photography
Year: 1917 (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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rtening of the bellows. Theeasiest way to make this is to obtain a stout steel or boneknitting needle, cut to the proper length and wrap the clothround quite tight and cement with a little cycle tire cement.Two small wire hooks should be driven into the back of thelens front and to the inside of the frame of the focussingscreen, the knitting needles can then be readily slipped intothese hooks. At the top and bottom of the cloth should besewn two narrow strips of elastic, which will naturally con-tract and expand. The lenses must be paired, and an important point is as totheir focus. Five inch lenses will be found good, but for all-round work three, five and seven inch will really be required.It is not necessary that they should be anastigmats. As amatter of fact, the old single or landscape lenses are quitegood enough for the purpose. Someone may raise the ques-tion of distortion of marginal lines, which is always given bythese lenses. But we do not use the extreme fields of the ^ 230
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MOONLIGHT ON JAMAICA BAY. T. L. JAMES. 231 lenses and even if they give distortion, it should not be over-looked that all, or nearly all. Stereoscopes also give distortionof the opposite character, so that the one cures the other.Naturally one can use anastigmats, but their cost is muchhigher. The separation of the lenses is an important matter andtheoretically it should be equal to the interpupillary separation,which is approximately 65 millimetres (= 2^ ins.). But thisseparation, which is correct for normal work, that is for ob-jects at normal distances, landscapes or architectural work, isincorrect for near objects, therefore the separation of thelenses should be adjustable. This is most important as some of the most striking stereo-scopic results are those of small objects taken quite close, forinstance, the feathery head of the dandelion makes a mostcharming picture. If the lenses are adjustable it is quite easy to decrease theseparation to the required extent by examining the fo

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