Abstract
RECENTLY, I have been photographing spectra in their natural colours with 35 mm. Dufaycolor film. The spectra were produced by a single 60° flint prism. 35 mm. film is used in a camera of 5 cm. focal length and, if this camera had been used by itself, the spectra would have been much too short. I therefore tried to photograph them through the telescope of the spectrometer ; that is, the telescope object glass and eyepiece were left in position and the camera placed immediately after the eyepiece. The telescope had a magnification of about 11 times, so this would increase the angular extent of the spectrum from 2½° to 27½°. I found that the field of view of the spectrometer eyepiece was too narrow, but on substituting the eyepiece of a prismatic field-glass which took in a cone of semivertical angle 128' instead of the previous 53', the experiment succeeded ; the visible spectrum covered the full breadth of the film and was in perfect focus from end to end.
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