6 
these images varies as the ratio of the conjugate object 
to image distance measured from the image generating 
mirror element. The gathering power depends, of course, 
on the total area contributing to the formation of images, 
i.e. on the mirror aperture. In order to obtain a full 
unobstructed light flux within the condensing system it 
is necessary to locate all structural parts of the light 
source and filters outside of the system’s aperture. 
This can be achieved by the proper selection of a plane 
which trims the reflecting segment off the ellipsoidal 
body. An economical way of producing such segments is 
by the replication process which requires a convex master 
ellipsoid of suitable dimensional and surface properties 
of sufficient strength to withstand the impact of the 
replication process. 
A condenser of the kind considered for a 120° super 
wide angle projection system requires besides a large 
aperture also a slightly larger axis of the master 
ellipsoid than that used with a 90° field system. 
Its parameters were selected as follows: 
major axis of ellipse 12.8” 
minor axis of ellipse 11.9” 
separation of focal points 120mm 
replicable surface of optical quality 
from 60° latitude above to 80° latitude 
below the equator. 
material: a special dense steel vacuum 
melted and forged 
In the past the production of a master of this kind 
by improvised equipment and by gradual approximation was 
a very tedious and expensive task. The increased demand 
for replications for photogrammetric and a number of