Film dimensions
| Format | Dimension | Surface (per sheet/roll) | • | • |
|---|---|---|---|---|
| 135 | 24mm x 36mm | 311 cm² (36 exp) | 1 | 0.67 |
| 120 | 61mm x 760mm | 464 cm² | 1.5 | 1 |
| 4×5 | 100mm x 125mm | 125 cm² | 0.4 | 0.27 |
The table below suggests how to select film exposure index (relative to box-speed) and adapt film development time (relative to datasheet) given an expected subject brightness range (SBR).[1]
| SBR | EI | Time | |
|---|---|---|---|
| L | - | - | rainy or foggy day |
| N | -2/3 | -15% | bright but cloudy day |
| H | -1 1/3 | -30% | bright sunny day |
In general, a rule of thumb is to[1]:
From another source (?), the following reccomendation is given: The table below suggests how to adjust film development to accomplish N+/- development.
| N-1 | -15% < N-1 < -25% |
|---|---|
| N+1 | +25% < N+1 < +40% |