| Emulsion. | Resolving Power. |
|---|---|
| Seed Graflex | 25 |
| Eastman Aerial Film | 37 |
| Hammer Ortho | 44 |
| Cramer Isonon | 48 |
| Cramer Spectrum Process | 57 |
| Eastman Portrait Film | 61 |
Tabulation of Requirements for Aerial Emulsions.—In terms of the sensitometric quantities just discussed the general requirements for aerial plates may be listed as follows:
1. Speed. The speed usually connected with the contrast and density required for the exposure times available is about 150 H & D. Faster plates in general have too low contrast, but the highest speed that will give the necessary contrast is desired.
2. Contrast. The contrast capable of development without fog should be from 1.5 to 2. This contrast should be produced by light of daylight quality, and, in orthochromatic and panchromatic plates, with the yellow or orange filters intended to be used with them. This contrast means a gamma infinity approaching 2.5.
3. Speed of development. A gamma of nearly 2 should be developed in 2½ minutes at 20 degrees C. in the developers recommended below.
4. Fog. Not over .25 for this degree of development, and not over .40 for six minutes development.
5. Color sensitiveness. This should in general be as high as possible. In terms of certain representative filters (described in a subsequent chapter) color sensitiveness should be such that with the white light speed above specified the relative exposures through the filters shall not be greater than as follows:
| No filter | Aero 1 | Aero 2 | #21 | #23a | #25 | |
|---|---|---|---|---|---|---|
| Panchromatic plate | 1 | 3 | 4.5 | 7 | 9 | 12 |
| Ortho plate | 1 | 2.5 | 3.5 | 6 |
Relative Behavior of Plates and Films.—The advantages of film from the standpoint of weight and bulk have been discussed in connection with aerial cameras. Were there no other considerations film would unquestionably be the most appropriate medium for aerial photography. There is, however, the question of ease of handling, to be treated in a subsequent chapter, and the question whether the purely photographic characteristics of film are satisfactory. Can the same speed, contrast, and color sensitiveness be obtained on film as on glass? Is the picture so obtained as permanent or reliable as the plate image?
It must be confessed that up to the present emulsions on film have not proved the equal of those on glass. It has been found by emulsion manufacturers that the same emulsion flowed on film and on glass gives better quality on the glass. Emulsions specially prepared for film fall somewhat short of the best plate emulsions. It has also been found harder to color-sensitize film, and to insure good keeping quality in the color sensitized product.