Long exposures at dusk and reciprocity
Past about one second most films respond less than the meter promises. For the water to turn to mist on a slow emulsion the corrected times get long quickly.
| Metered | Exposed for |
|---|---|
| 1 s | 1 s |
| 4 s | 6 s |
| 15 s | 35 s |
| 30 s | 1 min 30 s |
| 1 min | 4 min |
The figures are for the traditional cubic-grain stock used here; tabular-grain films need much less correction. Light falls while the shutter is open at dusk, so meter again half-way and add what was lost.