At the end of the chimney there is a variable width slot parallel to the 
generatrices of the cylinder, by means of which the exposure of the film is 
possible. 
We define the following elements ín suoh a typical cameras 
a) Camera axis. This is the axis of the oylinder on which the film is laid. 
b) Rotation axis of the scanning. This is the axis around which the element 
whioh accomplishes the scanning rotates. 
c) IMC axis. This is the direction in which the elements making up the IMC de 
vioe move. 
d) Scanning plane, This is the plane passing through two points of the axis 
of the slot and through the internal nodal point of the lens. We oan di 
stinguish the internal scanning plane thus defined, and the external 
scanning plane defined by the 1st nodal point and by 78traight lines homolo 
gous to the conjuctions of the two above mentioned points and the 2nd nodal 
. point. 
e) Scanning angle. This is the angle that the scanning plane forms with a de 
termined plane taken as a reference. | 
This plane can be an arbitrary one, but the one corresponding to the maxi 
mum speed of the IMC is assumed as a reference plane. 
1.3 = IMAGE MOTION CORRECTION DEVICE. 
Tt is well known that the IMC can be defined "the device which elimina 
tes or reduces the relative image-film speed, to eliminate or reduce the 
effects of blurring which are caused thereby". First of all we notice that 
it is necessary to use the IMC because it is impossible to accomplish, under 
certain conditions, extremely high scanning speed. In fact, regardless from 
motion conditions of the aircraft during the photogram shooting, after de 
fining minimum tolerable blurring, it is always possible to compute the scan 
ning duration for which, without the IMC, the blurring in any point whatever 
of the photogram does not exceed the prefixed limits, The duration which can 
then be inferred in the case of fast aircrafts, and at low altitude are never 
theless extremely short and therefore cannot be constructively accomplished. 
The maximum scanning speed being fixed (speed of rotation of the prism and 
the speed of the film), the minimum times of exposure for a strip of the film 
corresponding to the slot are fixed. It can be therefore established that du 
ring the impression of a strip, the blurring of the image is not tolerable 
and the IMC is introduced to eliminate it. Since the IMC must be used, it is 
logical that it must work in such a manner as to eliminate, at least theoreti 
cally, the relative image-film speeds. 
This premise is useful for presenting the question of the IMC from the 
point of view of the geometry of the camera. It can in fact be immediately in 
ferred, that operating imperfections of the IMC do not produce perceptible de 
creases in the quality of the image; for a photo-interpretative use of the pho 
tograms produced no problem arises, While, on the contrary, from the point of view! 
the geometry of internal bundle of rays the correct evaluation of the contribu 
tion of the IMC becomes essential. 
We can illustrate this better with an example. In the case of a panoramic 
camera having speed V, at a relative altitude H, on a supposely plane terrain, 
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