File:The American annual of photography (1922) (14595119518).jpg

Identifier: americanannualof36newy (find matches)
Title: The American annual of photography
Year: 1922 (1920s)
Authors:
Subjects: Photography
Publisher: New York : Tennant and Ward
Contributing Library: Harold B. Lee Library
Digitizing Sponsor: Brigham Young University

View Book Page: Book Viewer
About This Book: Catalog Entry
View All Images: All Images From Book
Click here to view book online to see this illustration in context in a browseable online version of this book.

Text Appearing Before Image:
ts may be combined toobtain doublets of different focal length; a set of three or fourof the single elements making possible a selection of six or tenfocal lengths. Several lenses of the Protar type are made today, eachhaving its individual claims for superiority, and the writer isglad to remark that nearly all of them are of high excellence.The only real disadvantage of the construction lies in the factthat, owing to the deep curves and numerous elements, it isvery costly to produce. Another type of lens which was and is deservedly popularhas three cemented elements in each half. The complete lensgives an excellent image over (at small stops) about ninetydegrees; its usual aperture is about F/6.8, and it can be reliedupon to do excellent work under any conditions when its speedis sufficient. As compared with the preceding type, the latter has a some-*vhat wider angle, but not quite so flat a field; the cost is lessbut it is much less readily combined in sets and the singlets do 2.=iO
Text Appearing After Image:
GILMER WINSTON. 251 not perform as perfectly unless stopped down to (in mostcases) F/16. Many lenses of the triple cemented type are produced, andthose by the really reliable makers are of high excellence. Another type of lens is composed of two symmetrical ele-ments, each of which consists of two cemented meniscuselements whose concave surfaces face the diaphragm. It usu-ally has a very flat field of about 65 degrees, within which anglethe definition is extremely critical at an aperture of aboutF/6.3. At small stops this angle is somewhat increased. Itcosts somewhat less to produce than many types, and slightvariations of glass are easily compensated by varying the sepa-ration of the elements. A rather unique type of lens we will term the Cooke type,since the Cooke lens is the most prominent example of it. Itis composed of three single elements which are separated byair spaces; the front and rear element are double convex,while the central lens is a double concave, more powerful than

Note About Images