An air nozzle used to operate a spinner on the Goerz Hypergon lens of 1900.
Toronto. The earliest camera lens designers were more concerned with plate coverage than aperture. Often a lens was described in terms of coverage – half plate, full plate, etc.
Numerous strategies were used to allow a greater coverage – mechanical devices like the little air fan Goerz used in its Hypergon lens to lower the light from the central rays, a special filter to reduce the light from the central rays like Zeiss used for its 1970s 15mm Hologon lens – or simply reduced apertures like the Leitz Hector 28mm f/6.3 and many other lenses used.
The Hypergon used its spinner for about 5/6 of the exposure to hold back light from the central rays. The last 1/6 of exposure, the little fan was flipped back and the central rays allowed to exposed the plate too.
The special Zeiss filter for the zeiss hologon filter was designed to reduce the light from the inner rays by being dark in the middle and progressively lighter to the edge. A neutral density coating was used so colour could be recorded.
In the case of reduced aperture, the smaller apertures have less fall off at the edges allowing a greater degree of coverage. For example Leitz limited the widest aperture of its earliest 28mm lens, the Hektor, to f/6.3. The Zeiss Protar series is catalogued in terms of coverage at maximum aperture size.
Normal and long focus lenses seemed to be more straight forward so the designer could concentrate on higher resolution, or lower distortion, or a larger aperture. The 135mm Hector/Elmar lenses by Leitz were often noted as having a wide coverage suitable as a normal lens for a larger camera than 35mm – a full plate camera for example.
