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the actual shutter speed setting in use
.
It is preferable that F is greater than or equal to
3
x
1
/
T
.
The recommendations made in Table 3.2 are for black and white film. Reliance should
not be placed on their application to colour film. Instead, the user should experiment
with several exposures to determine the most suitable. Acceptable pictures on colour
films having the same speed ratings as the black and white films given may be obtained
from the use of the table, or an increase in exposure may be found necessary
.
Number of flashes occuring while
the shutter is open:
1
2
4
8
(Flash rate less than 25
Hz)
Exposure-time in
seconds:
1/30
1/15
1/8
1/4
(Flash rate greater than 25
Hz)
Aperture settings for Kodak Tri-X
f/4
f/5,6
f/8
f/11
Aperture settings for Kodak Plus-X
f/5,6
f/8
f/11
f/16
800 157
Table 3 .2. Recommended exposures for photography with the 4912
If the purpose of using the 491
2
for photography is to obtain a clear picture of a moving
object, it is important to ensure that the illumination of the object by the 491
2
predon:,i-
nates over its illumination by other light sources. This can be checked in cases of uncer-
tainty by measuring the exposure required in the absence of the 491
2,
using an ordi-
nary photographic exposure meter
.
The measured exposure should significantly exceed
that recommended in the Table, if an acceptable picture is to be obtained.
15
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