File:The American annual of photography (1922) (14595154207).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

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th groovesfor holding opaque slides, cut in the side edges of the revers-ible back. This arrangement permitted him to obtain fourdifferent exposures on one plate, or Eastman flat film, bysimply moving the opaque slides from one side to the other.Instead of using an apparatus with removable back and slides,a camera that does not possess this can be used as follows:A piece of heavy opaque paper—the size of the opening whenthe back is removed—is used. Cut one-fourth of the entirepaper away, making right angles with the edges. This can 135 be used as the mask to obtain the four desired exposures toshow whether the speeds are the same or whether the samevary. The four or three variant exposures should correspondto the method of analysis as outhned below. From the reproduction given—which has been numberedfrom I to 4 to facilitate the pursuance of this analysis—it willreadily be seen that number i is approximately one-half asdense as number 2; also number 3 is four times as dense as
Text Appearing After Image:
No. I. i/ioo sec. exposure No. 3. 1/25 sec. exposure. No. 2. 1/50 sec. exposure. No. 4. 1/5 sec. exposure. Figure i. number i and twice as dense as number 2. Number i receivedthe exposure marked i/ioo; number 2 the exposure marked1/50; number 3 exposure 1/25 and number 4 exposure 1/5.One easily notices since number 2 is twice as dense as numberI, and that speed i/ioo was used for i and speed 1/50 for 2,that these speeds are in the ratio of i to 2, i.e., that i/ioois twice as fast as 1/50. The same can be shown and provedwith number 3 which is one-fourth as rapid as number i, andone-half as fast as number 2. Number i compared with num-ber 4 shows that it is twenty times the speed, the density ofwhich was determined by means of a microscope as well as 136

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