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April, 1934
The INTERNATIONAL PHOTOGRAPHE \<
Twenty three
is made, development, etc. There is no uniformity in this matter, each laboratory employing its own method. There is, however, an aid which compensates for all these inaccuracies, and that is the latitude of the emulsion. Every emulsion can stand a definite amount of deviation from the correct exposure, either under, or over, and still produce a correctly exposed negative. Panchromatic films seem to have wider latitudes than orthochromatic emulsions.
H. & 1). numbers for a film may be available and the meter employed utilizes Scheiner degrees or vice versa. For convenience I am listing below two tables, the first containing various films and their speeds in Scheiner decrees, and the second a comparison between Scheiner degrees and H. & I), numbers:
Table of Film Speeds
Daylight Mazda
Agfa Fine-Grain Plenachrome 21
Agfa Superpan ----- 23 25
DuPont Orthochromatic 17
DuPont Panchromatic 18
DuPont Superior .24
DuPont Special Panchromatic 23
DuPont Micropan ---- 16
Eastman Kodak Orthochromatic 17
Eastman Panatomic 19
Eastman Kodak Panchromatic 17
Eastman Kodak Type 2 18 Eastman Kodak Supersensitive
Panchromatic ---- 23
Eastman Kodak Verichrome 19
Gavaert Superchrome Express 21
Savaert Superchrome Express 21
Mimosa Extrema ---- 21
Perutz Orthochromatic 17
Perutz Persenso ---- 21
Selo Orthochromatic 19
Selo Panchromatic ---- 21 23
Voigtlander ------ 23
Scheiner Degrees and H. & D. Numbers
Scheiner No. H. & D. No
10 56
11 72
12 91
13 117
14 150
15 190
16 240
1 7 308
18 390
19 500
20
27 25 18
22 21 22
26
20
21 22 23 24
25 26 27 28 29 30 31 32
636
800
1,050
1,300 1,700 2,100 2.700 3,500 4,400 5,600 7,200 'Moo 11,600
Despite the accuracy of exposure meters there is still a factor left to personal judgment — the color of the light. In the above table of emulsion speed provision is made for the speed of panchromatic films to mazda light. Daylight, however, varies in its chromatic characteristics. During noon it is what we may term normal. In the early morning or late afternoon it usually exhibits large quantities of red and yellow. Exposure meters measure the actinic strength of light in relation to its quantity, and not as to its color. A panchromatic and an orthochromatic film which have the same speed at noon will differ in speed at the mentioned times, when daylight contains large amounts of yellow and red. In this case the panchromatic emulsion will be of greater speed, due to its greater sensitivity to the longer wavelengths of light.
With the use of a reliable meter the photographer should experience no difficulty in obtaining correct exposures. He should, however, guard against overexposure.
Candid Photography: Of the types of photography to which the miniature camera has been a great stimulus, candid photography is perhaps the most outstanding. Since miniature cameras have gained popularity candid photography has also come into vogue. When considering newspapers candid photographs of celebrities engaged in certain activities always were prize catches. It was, however, difficult to obtain such photographs with large cameras. Many large newspapers now provide their staff men with miniature cameras and many of the candid "shots" seen in newspapers are made with baby cameras.
Cameras like the Leica, Contax and Foth Derby which allow lenses to be interchanged, are best suited to this type of work. Besides the universal f:3.5 lens usually supplied with miniature cameras, a telephoto and speed lens are great helps in candid photography. ( Turn to Page 28)
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