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2.5 | Changes in Calibrated Focal Length
Regarding the accuracy of photogrammetric plotting processes, the
calibrated focal length is not as important as the distortion.
Therefore, it is only ascertained with an accuracy of t 0,02 mm
during calibration. Nevertheless the influence of air pressure
and temperature on the calibrated focal length is of interest.
It results from the alteration of the focal length and the
distortion of radial distance 140 mm. The total influence is
listed below:
Changes in Calibrated
installed Exposed to atmosphere
in pres-
surized cabin
(with cover (without cover glass)
glass)
lens temp. lens temp.
constant +7 dep.on ext.temp.
flight height 6 km | 1^ km 6 km 14 km| 6 km 14 km
S-Pleogon A4/85 -0,005 | -0,019 | -0,025 | -0,038 |-0,045 |-0,076
Pleogon A 4/153 -0,020 | -0,038 | -0,036 | -0,058 |-0,047 |-0,080
Toparon A,5,6/210 | +0,014 | -0,007 | -0,021 | -0,013 -0,082 |-0,127
Topar A 5,6/305 40,012 | -0,01? | -0,025 -0,028 |-0,110 |-0,172
- table 4
Focal Length (in mm)-
You will note that these changes may reach the accuracy and should
therefore be taken into consideration. Also, it is obvious that
the alterations are by no means proportional to the focal length,
but depend upon the type of lens.