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Published online by Cambridge University Press: 14 August 2015
The objective prism (or grating) is the most efficient stellar spectrograph since it suffers no light losses at a slit and - compared to a slit spectrograph - only small losses in the camera optics. However, objective prism spectra have two principal disadvantages:
(1) the spectral resolution (and consequently the sharpness of spectral features) depends on the seeing, which may vary from plate to plate.
(2) quantitative measurements are difficult because of the difficulty in obtaining an exact photographic calibration; no comparison spectrum can be placed near the stellar spectra.