A manual of photographic chemistry, theoretical and practical . s, and the wide-angle non-distorting or architect-ural lens. Between each of these classifications it is difficultto draw a hard-and-fast line, seeing that some objectives arenow constructed which fulfill more than one of the requirementsnamed. 338 OPTICS OF PHOTt)GRAPHY. The Single Landscape Lens.—For ordinary landscapes nolens or form of objective has yet been introduced which sur-passes the single achromatic lens, which, when properly con-structed, gives pictures possessing sharpness and brilliance, in-cludes a wide angle of su
A manual of photographic chemistry, theoretical and practical . s, and the wide-angle non-distorting or architect-ural lens. Between each of these classifications it is difficultto draw a hard-and-fast line, seeing that some objectives arenow constructed which fulfill more than one of the requirementsnamed. 338 OPTICS OF PHOTt)GRAPHY. The Single Landscape Lens.—For ordinary landscapes nolens or form of objective has yet been introduced which sur-passes the single achromatic lens, which, when properly con-structed, gives pictures possessing sharpness and brilliance, in-cludes a wide angle of subject, and works with a reasonabledegree of rapidity. The form of the single achromatic land-scape lens is shown in Fig, 33, in which an achromatic /f*^.. \ Fig. 33. meniscus is placed at one end of the tube, there being adiaphragm in front of it. At this stage we may fittingly introduce a diagram whichexplains the useful part subserved by the diaphragm or stopwhen placed in front of a landscape lens. In this diagram a number of rays O, Z, and those between. Fig. 34. them, are represented as impinging obliquely upon the flattestsurface of a lens, L, all of them, however, taking differentcourses as regards their crossing each other after being trans-mitted. The image of any object would be quite devoid ofsharpness, and be hazy, owing to the ray Z being refracted in agreater degree than any others of those between it and the LENSES. 339 upper boundary ray O. If tlie transmitted ray Z, instead oftaking the coarse Z, went straight to 0,the intermediate raysdoing the same, then would we have a perfect single leris;but such is not the case, owing to the aberration caused bythe spherical surface of the glass. Spherical aberration, itmay here be once more remarked, is that property in a lenswhereby parallel rays falling either obliquely or axially uponits surface undergo such different degrees of refraction as pre-vent them meeting at one point. - The function of a diaphragm, as appl
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