Abstract
THE new f/0.36 spectrographic object-glass referred to in Dr. G. E. Hale's article in our Supplement this week on the Astrophysical Observatory of the California Institute of Technology was designed primarily with the object of increasing the range within which distant nebulae can be investigated by spectrographic methods. The attention of the British Scientific Instrument Research Association was directed to the need for such a lens as the result of a conversation between Dr. Hale and Sir Herbert Jackson, who was at that time Director of Research of the Association. Spectra obtained with the f/O.59 lens developed by Dr. W. B. Ray ton had indicated that the apparent velocities of recession of the more remote nebulae increase with increased distance of the nebulae. This had been verified by observations on nebulae so remote that satisfactory exposures were obtainable only with the greatest difficulty; but in view of the important implication's of these results it was urgently desired to extend the range of investigation to the utmost possible limit. It was obvious that, if any large increase of range were to be obtained, the new spectrographic object-glass would need to be much more ‘rapid’ than the Rayton lens, that is, the ‘focal-ratio’ aperture would have to be considerably greater than//O-59. To obtain any large increase of aperture, an ‘immersion-type’ of lens would be needed, that is, a lens to be used in immersion contact with the photographic film or plate on which the spectrum was to be photographed. With such a lens it appeared probable that a ‘numerical aperture’ of 1-4 (equivalent to f/O.35) should be obtainable, and consideration was given, therefore, to the problems which would arise in designing, constructing and using a lens of this type.
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The New Spectrograph Objective for the 200-inch Reflector. Nature 137, 218 (1936). https://doi.org/10.1038/137218a0
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DOI: https://doi.org/10.1038/137218a0