Abstract

An f:1.0 spectrograph camera with a nearly flat field was designed by splitting the symmetrical ball lens of Sutton and adding correcting components. The resulting 7-element objective has longitudinal spherical aberration not exceeding 0.001 mm between 7000A and 9000A.

The camera is constructed so that all adjustments of tilt and focus are made from behind the plateholder. The plate emulsion is kept within 0.025 mm of the focal plane even when the camera is operated upside down.

In astronomical use the camera photographs several hundred angstroms of spectrum at one time on flat plates, with good definition through the range 4000A to 9000A. As compared to modified Schmidt cameras, it has the disadvantage of a field limited to 7 degrees by vignetting, but is comparable in light efficiency, and has the greater convenience of allowing the use of glass plates large enough to carry multiple exposures.

© 1951 Optical Society of America

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Figures (6)

Fig. 1
Fig. 1

First modification of symmetrical ball lens.

Fig. 2
Fig. 2

Second modification, containing additional elements.

Fig. 3
Fig. 3

Cross section of camera with the lens in place. Diameter of tube at front of lens (bottom of diagram) is 4 1 8 in.

Fig. 4
Fig. 4

Top view of tilt cylinder in the focusing tube.

Fig. 5
Fig. 5

General view of camera. One plateholder is in place, and another is shown alongside.

Fig. 6
Fig. 6

Prismatic spectrogram of the star γ Cygni, with iron comparison spectrum. Enlargement 21×.