. The book of photography; practical, theoretical and applied. EYEPIECE Fig. 79J.—Her^schels Reflecting Telescope. seem to have a uniformly even surface,but if a ray of light be made to fall on itand then enter the eye by reflection itrarely remains a distinct spot from everypoint of view. A great drawback in thesetelescopes is the presence of the appara-tus for directing the reflected ravs into. jEYEPiECE Fig. 800.—Newtons Reflecting Telescope. the eyepiece. This generally stops therays which would otherwise fall on thecentre of the mirror. In the diagram ofthe Newton telescope. Fig. 800, m r
. The book of photography; practical, theoretical and applied. EYEPIECE Fig. 79J.—Her^schels Reflecting Telescope. seem to have a uniformly even surface,but if a ray of light be made to fall on itand then enter the eye by reflection itrarely remains a distinct spot from everypoint of view. A great drawback in thesetelescopes is the presence of the appara-tus for directing the reflected ravs into. jEYEPiECE Fig. 800.—Newtons Reflecting Telescope. the eyepiece. This generally stops therays which would otherwise fall on thecentre of the mirror. In the diagram ofthe Newton telescope. Fig. 800, m repre-sents a piece of plane silvered glass or atotally reflecting prism. Its interferencewith the rays can be easily seen. In laterforms of telescopes, object mirrors havebeen made by grinding glass to theproper curvature and thickly silvering andpolishing the ground surface. Mirrors donot seem to have been much favoured forphotogiaphic purposes, in spite of the factthat rays of all wave-lengths generallycome to the same focus, although the caseof the Crossley reflector used at the Lickobservatory may be cited as an exception. Position of Eyepieces and CamerasFOR Reflectors. In every case, the position of the eye-piece indicates where the camera shouldbe attached, since the tube which carriesthe eyepiece can be made to support thecamera lens. The eyepiece is always re-moved before attac
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