A First Book of the Lens; An Elementary Treatise on the Action and Use of the Photographic Lens
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. 1901 edition. Excerpt: ...from outward distortion it will take the form shown at C, which is known as cushion distortion. All lines that pass through the principal axis of the lens remain straight while all others become curved, on which account diaphragm distortion is often termed curvilinear distortion, and a lens free from distortion is called rectilinear. It appears, however, to be possible for a certain amount off distortion to be present without the production of any marked curvilinear effects. The best test for diaphragm distortion is therefore the comparison of proportions. For example, if we take an equally divided object, and the lens throws an equally divided image on a screen parallel to the object, diaphragm distortion must be absent. Speaking generally, distortion is diminished by placing the diaphragm at or near the crossing-point of the lens. This condition cannot be fulfilled with a single meniscus lens, as the crossing-point is on the convex side of the lens and the diaphragm must be on the concave side to diminish curvature of the field (figs. 50 and 51). In a doublet with the crossing-point between the lenses the diaphragm can be placed in the required position, but with a doublet of the periscopic form it cannot. In the telephotographic lens, which is essentially a combination of a positive and It may also be correctly described as "Orthoscopic." The particular lens (now out of date) known by this title was, however, thus christened in error, for it eventually proved to be non-rectilinear. a negative system, distortion may be obviated by making each lens itself rectilinear. Practically each lens has a diaphragm at its own crossing-point, hence the whole is free from distortion. It should be noted that combinations of lenses may show...
- 189 x 246 x 3mm | 100g
- 13 Sep 2013
- United States
- black & white illustrations