ac yy 2 LUE ST Se NAN aS TARO SPY Manual en patte civi AMA in of CE apo PR A E C a at Os potes ded
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2:b.. Changes in Focus
Changes in focus should not be mixed up with the changes in
calibrated focal length mentioned before. With allowance being
made for the focussing distance, the aerial survey camera as a
fixed-focus camera is adjusted in the laboratory in such a way
that the film plane lies in the plane of best possible image
quality during exposure. Changes in focus are variations of this
adjustment in the optical axis. They mainly result from the re-
duction of air pressure with increasing flight height and only
to a smaller degree from changes in temperature, The total
influence is as follows:
Installed in Exposed to atmosphere
pressurized
cabin
with cover glass without cover glass
cover glass @ 720mm lens temp. 9 lens temp.
cover glass thickn. constant +7 C | dependent on
45mm ext. temp.
flight height |pressurized acc.2km | 6 km 14 km |6 km | 14km
S-Pleogon A4/85 -0,03 -0,04 -0,07 | -0,01 | -0,05
Pleogon Ah/153 -0,04 -0,07 | -0,15 | -0,0^ | -0,09
Toparon A5,6/ -0,05 -0,10 | -0,17 |-0,08 | -0,1^
210
Topar A5,6/505 -0,07 -0,15 0,25 («0,13 40,23
- table 5
Changes in Focus (in mm) -
The list clearly demonstrates that changes in focus reach amounts
which can not always remain neglected. The tolerable limit
depends upon the aperture cf the lens. Under practical flight
conditions O.0^ to 0.06 mm could be accepted for those with f/4,
and about 0.06 to 0.09 mm for those with f/5.6.