Resolving power. Some developing processes and conditions will introduce bad grain into the negative. Hence the resolving power which a developer brings up must be investigated among its other characteristics.
Practical Developers for Aerial Negatives.—In the English service a pyro metol developer was generally used, producing stained negatives. The French, American and Italian practice was to use metol-hydrochinon, without staining. A special chlor-hydrochinon developer, worked out by the Eastman Research Laboratory for the United States Air Service, has probably the greatest merit of any yet tried. A comparison, given below, between it and a pyro metol formula used on a representative plate, illustrates the use of the various bases of study given above.
Pyro Formula
| Solution A | Solution B |
|---|---|
| Pyro, 3.75 grams | Sodium carbonate, 53 g |
| Potassium metabisulphite, 3.75 g | |
| Metol, 3.05 g | |
| Potassium bromide, 1.5 g | |
| Water, 500 c.c. | Water, 500 c.c. |
Use 1 part of A to 1 of B
Chlorhydrochinon Formula
| Solution A | Solution B |
|---|---|
| Chlorhydrochinon, 25 g | Sodium carbonate, 30 g |
| Metol, 6 g | Sodium hydrate, 10 g |
| Sodium bisulphite, 2.5 g | Potassium bromide, 3 g |
| Sodium sulphite, 25 g | |
| Water to 670 c.c. | Water to 330 c.c. |
Use 2 parts of A to 1 of B
| Pyro | Chlorhydrochinon | |
|---|---|---|
| H & D speed | 150 | 180 |
| Gamma infinity | 1.45 | 2.12 |
| Fog (at maximum gamma) | .32 | .60 |
| Time of appearance | 5 seconds | 5 seconds |
| Watkins factor | 25 | 10 |
| Velocity factor “κ” | .320 | .400 |
| Temperature coefficient | 1.40 | 2.0 |
| Temperature limits | 4° to 32° C | 4° to 32° C |
| Keeping power | 45 minutes | 8 days |
| Exhaustion (100 c.c.) | 30 sq. in. | 300 sq. inches |
| Dilution coefficient | 2 | 2 |
| Color coefficient | 1.50 | 1.00 |
| Resolving power | 47 | 53 |
Owing to the difficulty of securing pure chlor-hydrochinon a metol hydrochinon of very similar properties has been worked out. Its composition is