Films are designed to react normally (inverse linear relationship
between aperture and shutter speed) for most shutter speeds. This
relationship does not hold for exposures that are extremely short
(1/1000 or faster) or long (1 second or longer). This is called a
reciprocity failure
(Digital cameras do not suffer from reciprocity failure but suffer
from noise buildup with long exposure)
The problem becomes most acute in night photography when the exposure
times are long. Short shutter speeds are not a problem
since most cameras do not have shutter speeds that fast.
Long exposure/Night photography:
Film becomes less sensitive to light as exposure time increases
resulting in under exposure. You need to compensate by increasing the
exposure time.
- Exposure time
| Indicated exposure |
|
Increase exposure time to: |
Tri-X (similar times for Arista Edu) |
T-Max |
| 1 sec |
|
|
1.5 sec |
1 sec |
| 2 sec |
|
|
4 sec |
N/A |
| 4 sec |
|
|
12 sec |
N/A |
| 10 sec |
|
|
50 sec |
15 sec |
| 20 sec |
|
|
2 min |
N/A |
| 40 sec |
|
|
4 min 40 sec |
N/A |
| 100 sec |
|
|
20 min |
5min |
- Development time
As the exposure increases, the highlights gain density and your
overall picture gains contrast. To compensate, it is suggested you
reduce development time by 10 - 30%.
- Metering
Most in-camera light meters are not sensitive enough to function at
night. You'll have to bracket extensively, but here
are a few starting points (based on 400 speed film) with reciprocity
failure already taken into account.
- 3-5 sec @ f5.6: city with direct street lighting
- 1 min @ f5.6: city with indirect street lighting
- 5 - 30 min @ f5.6: landscape outside city
- 1 - 4 hrs @ f5.6: landscape in total darkness
In order to keep the shutter open longer than a preset value, use
the
bulb setting (often indicated by
B).