ower density 
necessary to 
e determined 
| be reduced 
mage motion 
- . 
plane, during 
er that bird's 
cing the time 
ra vibration. 
from camera 
> motion will 
the minimum 
stion remains, 
le and there- 
less than 0.6 
|] Trott, in. a 
he American 
1 motion and 
n 
en, somewhat 
re now added 
in Resolution 
600 
R 
14% 
120 
60 
| 40 
| 30 
| 
20 
the speed of 
5280 X 12 X 25400 
V. (in microns per sec) = S.V, (in M.P.H.) x ET 
( per sec) pun J 3600 
and since the Toler- 
; BUS oo 300 400 : 
able Image Motion M (in microns) = — | or = J) where R is the lens-film resolution 
R 
Sia 2 s 5 : 300 400 
in lines/mm. the Tolerable Time of Exposure (in secs.) = — [| or — 
RV; RV; 
1 1 1 
= apos approx — ———— lor ————.. 
1485 R.S.V, 1500 S.V, 1100 R.S.V, 
or, since shutter speeds are indicated as fractions of sec, 1/50, 1/230 etc., 
the denominator T- = 1500 R-S.V, (or 1100 R. S.V. y. 
E.g. when the Resolution R = 20 lines per mm 
the scale S — 1:15840 
the ground speed V, — 125 M.P.H. 
1500 X 125 x 20 
T! = - — 240 (or 180) 
15840 
Jorg 1 
E = - Se Or —— sec. 
240 180 
or, more specifically, when R — 20 lines/mm. f — 6.0 in. and H — flying height, 
> 1 
Since S 2 — 
2H 
1500 X 20. 15000 _ 11000 
= : V, = = plor —V, 
2H H H 
; 1 
Or at 15000 ft. (or 11000 ft.) and 100 M.P.H., the required shutter speed = sec. 
100 
(2) Considering rotational vibration of tbe camera. 
Motion of the image due to rotational vibration may not be known, but cannot be 
assumed to be negligible. In the absence of more specific information it may be 
assumed that the frequency of vibration is related to the RPM of the engine(s). If so, 
it is probable that the rotational movement of the camera during exposure can be 
reduced to less than half its total amplitude by using a time of exposure equal to 1/6 
the time of one engine cycle, e.g. at 1800 RPM or 30 RPS or 1/30 sec. per cycle, if an 
exposure of 1/180 sec. is used (1/6 cycle) the movement will be less than 1/2 the 
: : ; ; x RPM 
maximum amplitude of vibration or T-!should be not less than "d 
This is an arbitrary restriction that must be modified to suit lens-film resolution 
when information is available regarding the particular camera-mount-plane combination. 
This time of exposure, or its modified value, should be used at the higher altitudes 
where ground speed is less critical, that is, T-' should be the greater of the two 
a RPM 
quantities 1500 (or 1100) R.S.V, or — —. 
Combined Remedies for Increasing Sharpness in the Negative. Image motion 
calls for a short time of exposure. Image spread calls for low density, which requires 
under development and over exposure. Fortunately it is not now necessary to “shut 
down” the aperture of a lens to obtain adequate resolution, and therefore adequate 
increased exposure and reduced time of exposure will, in most cases, be possible—by the 
use of a larger aperture and faster shutter. Results already obtained with a moderate 
application of such changes give ample proof of its value. 
5