the frame sequence and, thus, overlap. Film flattening was 
effected by the action of the dynamic pressure built up in 
an outboard tube, 
The camera mount, consisting of a tubular gteel frame, permitted 
both drift correction and tilting up to 47 from the horizontal. 
The advancements made in the following years were principally 
directed at automating the operating cycle and improving 
optical performence, The latter was mainly achieved by the 
designing of special lenses having, by the standards of the 
time, low distortion and low field curvature, In addition, 
the RMK C/2 developed in 1925 already had a detachable finder 
scope. Other improvements over the earlier model were the 
210mm f/4.5 lens, selectable shutter speeds of 1/75, 1/100, 
1/130 and 1/160 s, and a frame counter, 
The RMK C/3 manufactured in 1926 already had a square image 
frame of 180 mm x 180 mm, which later became the standard 
international format, The lens was a 210mm f/4,5 Orthometar, 
In parallel with the continuous improvement of the serial 
cameras, Jena also advanced its manually operated single-shot 
cameras, with both plate and film magazines. Mentioning each 
and every model here would, however, exceed the scope of this 
report. 
Another essential innovation was introduced in 1928 with the 
RMK C/5-Perseus (Fig.5). It was the first camera to have a 
control unit for drift correction and overlap control by 
means of a travelling grid and a course line visible together 
with the ground image on a ground-glass screen, An upgraded 
version designated C/5a (Spica) was driven by a 12V, 100W 
d.c. motor. 
From 1928, the Jena works designed and built various models 
of two-channel mapping cameras as well a four-channel one, 
the AxRMK C/1, Their internal parameters were based on those 
of the respective single-lens cameras from which they were 
derived, For their technical data see ref. /1/. 
The continuous advancements were frequently stimulated by 
the practical requirements of the users, One such requirement, 
the free selection (within certain limits) of the flying 
height at a given photoscale, led to an innovation in the 
first half of the thirties automatic  high-precision cameras 
with interchangeable lens cones of different focal lengths. 
The RMK S 19819 (Fig. 6) with the standard 180mm x 180 mm 
frame size, for example, was available with 135mm, 210mm, 
300mm and 500mm lens cones, An electric drive module with 
multistep gear, finder scope or ground-glass viewfinder could 
be fitted, 
The development of peripheral modules such as the horizon 
chamber (for the 210mm lens cone) for determining photo tilt, 
and the statoscope recording chamber aimed at a further 
enhancement of performance capabilities and operating con- 
venience, 
The introduction of the travelling grid, which moved acrosss 
the ground-glass viewfinder at infinitely controllable speeds, 
62