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On the Adjustment and Testing of Telescopic Objectives: (English)

On the Adjustment and Testing of Telescopic Objectives: (English)

          
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About the Book

This historic book may have numerous typos, missing text or index. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. 1896. Not illustrated. Excerpt: ... or, if a nearer approach of the flanges is impracticable, then the same effect will be produced by pushing out the objective at a point opposite to su and this may of course be effected by separating the flanges by means of both pairs of counter screws s, and s, the adjustment being equally divided between them. Or, again, if the counter-cell should require pushing off at or near s it may be done either by means of the screws s, or by pushing in by means of the two pairs of counterscrews s and s dividing the adjustment between them. In order to get at these counter-screws, in the case of some telescopes, it may be necessary to remove the dew-cap. If it is desired to see whether the objective is correctly adjusted or not, the telescope should be directed to some moderately bright star at a good altitude and its image brought to the centre of the field of the eye-piece, which should be of medium power. However good the objective may really be, no really sharp image of the star will be obtained if it is much out of adjustment. If the O.G. is of the first type, then the best possible focus will show a fan shaped appearance like Fig. 10 (c)* of very appreciable size instead of a minute spurious disc. And if the eye-piece be racked in and out of focus alternately the star's light will then be noticed to spread out into a more or less pear shaped luminosity, the smaller end being the brightest. This appearance is similarly situated whether the eye-piece is within focus or beyond focus, and is caused by the objective being too near to the eye-piece at that side corresponding to the smaller and brighter end of the pear shaped appearance. Thus if the latter shows towards the observer's left hand, as in Fig. 10 (a), the fault may b...


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Product Details
  • ISBN-13: 9780217194280
  • Publisher: General Books
  • Publisher Imprint: General Books
  • Height: 246 mm
  • No of Pages: 38
  • Series Title: English
  • Weight: 86 gr
  • ISBN-10: 0217194281
  • Publisher Date: 01 Jan 2012
  • Binding: Paperback
  • Language: English
  • Returnable: N
  • Spine Width: 2 mm
  • Width: 189 mm


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