Characteristics of striæ in optical glass . Fig. II.—Rolled window plate of Fig. 10 viewed flatwise4. STRI^ AND DEFINITION The effect of striae upon definition of an image produced by anoptical system in which they are present is an important question,to which it is difficult to give a definite answer. In general, it isobvious that striae which are sufficiently heavy and dense will iSm«^^] ^^^^^ ^^ Optical Glass 83 injure the definition, and a mere glance edgewise through thewindow plate of Fig. 10 or through the plate of Fig. 13, at a straightedge, makes it evident that such irregular refract
Characteristics of striæ in optical glass . Fig. II.—Rolled window plate of Fig. 10 viewed flatwise4. STRI^ AND DEFINITION The effect of striae upon definition of an image produced by anoptical system in which they are present is an important question,to which it is difficult to give a definite answer. In general, it isobvious that striae which are sufficiently heavy and dense will iSm«^^] ^^^^^ ^^ Optical Glass 83 injure the definition, and a mere glance edgewise through thewindow plate of Fig. 10 or through the plate of Fig. 13, at a straightedge, makes it evident that such irregular refraction as is exhibitedby these plates seriously blurs the image. The effect of suchstriae is shown in Fig. 15, which presents images of an artificialstar, as seen first without (a) and then with the plate Fig. 12.—Rolled window plate of Fig. 10 viewed at an angle 0/45° The images {h, c) seen through the flat of the window plate arevery little inferior to those obtained with a clear aperture, whereasthe images (d, e, f), viewed through the polished edges, are blurredon accotint of the pronounced scattering of the light. That dense striae are seriously injurious to definition is thenevident. However, there are many good lenses which contain a
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