Table I 
Focal length 
of survey 
camera 
f 
c 
flax, nadir 
distance 
T? 
21 cm 
21 9 
15 
15 
11.5 
11.5 
10 
10 
8.8 
CO 
CO 
The ranges of the E4 are quite sufficient for direct rectification 
□f all near-vertical photography up to a maximum image size of 
23cm x 23cm (9" x 9") and also for double-convergent normal angle 
photography uhich is houever extremely rare. Only with double con 
vergent wide angle photography is it necessary to rectify in two 
steps, but this case is also hardly likely to occur since that 
technique has been replaced by the use of super wide angle photo 
graphy. 
In choosing the lens there uas no question of doing other than 
adopting the Reprogon f/5.6 uhich is computed by Dr.h.c. L.Bertele 
and is uell knoun in conjunction uith the Wild VG1 Enlarger. This 
tuelve-element high performance lens of the Aviogon type has all 
the optical properties required for a good rectifier lens. Due to 
its relatively short focal length of 15 cm (6") it has been possible 
to reduce the height of the E4 to 2.80 m (9*2") in spite of the 
7x maximum enlargement. The E4 can therefore be set up uithout 
difficulties in uork rooms of normal height. The angular field is 
82^, so that uithin the full range of enlargement all negatives 
up to a size of 23cm x 23cm can be imaged sharply right into the 
picture corners. Even uith opened diaphragm, the resolving pouer 
of the Reprogon is considerably higher than that recorded by the 
best aerial photographs. At the aperture f/8 the resolution is