Items related to Photo-micrography
This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1899 Excerpt: ...found to be correct. What is more to the point, the argument also shows that the limit of dry objectives is N. A. 1-o, because all the outside rays will be lost without the interposition of some homogeneous substance to optically join up the gap between the objective and the cover-glass. It is for this reason that immersion lenses are often called homogeneous systems. Another point not to be forgotten is that as the cover-glasses vaiy in thickness and density, so the bending of B D may vary in direct accordance, and it is to obviate this that dry lenses of high N. A. are provided with a "cover-glass adjustment," which so regulates the performance of the objective as to accommodate it to the differences in question. To practise the user to arrange the adjustment, as well as for other reasons, the firm of Zeiss sell a slip upon which several cover-glasses of known thickness are placed, and as the firm mark the adjustments for different thickness of cover-glass on the objective itself, it enables the beginner to practise over and over again the art of getting his adjustment correctly by sight, and then proving his result, until he is quite an adept, by comparing the figures on the coverglass with those on his objective. This object lesson, which requires some patient practice and learning, is of great service, especially to the photo-micrographer, as it will be seen hereafter when speaking of depth of vision in lenses (page 87). It will then be shown a great deal of accurate vision is dependent on the accommodation of the eye--hence the greater amount of accuracy in focussing, &c, is required when photographing an object where the accommodation of the eye does not come into play, and every adjustment to improve such focussing must be employed. In...
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- PublisherRareBooksClub.com
- Publication date2012
- ISBN 10 1236260880
- ISBN 13 9781236260888
- BindingPaperback
- Number of pages58
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