Miscellaneous Papers of the University Observatory, Oxford Volume 2

Miscellaneous Papers of the University Observatory, Oxford Volume 2

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This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1905 edition. Excerpt: ...final coordinate is given here with the same units as in the above table: ' The distortion arises from want of flatness in the field, and to this again is due a marked absence of good definition at a distance from the centre. Any appreciable distortion within the field to be covered, even when not complicated by bad definition, is inconvenient as requiring corrections which might be obviated by better optical means. That this can be done may be inferred from the performance of photographic lenses. It may be necessary to use a doublet, as in the Cambridge instrument, or at least a triple lens. It is to raise this question that the present note has been written. Can objectives be obtained which are sensibly free from distortion, and is it necessary to substitute for the single objective an optical combination of greater complexity 'I Since the adoption of the reseau as an essential aid in the work of measuring, the machines employed for measuring astronomical photographs seem to fall under three distinct classes: (a) The perpendicular threads in the focus of the microscope are fixed during the measurement. Relative motions in perpendicular directions between the plate and the microscope are produced by micrometer screws, so that the star and the four sides of the containing reseau square can be brought under the microscope threads. The mechanical arrangement of the apparatus The answer to this first question must be taken to be in the aifirmative, for the Cambridge machine appears to be entirely free from distortion of an amount which can be detected. It is not so clear whether the capacity of a properly designed single objective is necessarily inadequate to the requirements. must be of a. high order of perfection, and the...show more

Product details

  • Paperback | 146 pages
  • 189 x 246 x 8mm | 272g
  • Rarebooksclub.com
  • United States
  • English
  • black & white illustrations
  • 1236926749
  • 9781236926746