The Dictionary Of Photography

A True Historic Record Of The Art & Practice Of Photography 100 Years Ago.

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have issued a new wide-angle euryscope, working at and Messrs. Voigtlander & Son have introduced two new wide-angle lenses, the one a landscape, composed of a bi-convex crown cemented to a bi-concave lens. Both glasses, of the new Jena material, are extremely light, and of little dispersive power, in great disproportion to the index of refraction; thus the bi-concave lens, which is usually a flint, is more like a crown glass lens. It subtends an angle of 76o has an exceedingly flat field, and distortion of the marginal lines is reduced to a
Fig. 97-
minimum ; working aperture, The other lens is a new
wide-angle euryscope, which works at'approx.), and includes an angle of 8oo. This also is constructed of the new glass. From its large aperture and short focus it is eminently suited for group work in confined situations, and for instantaneous or hand cameras. In 1889 Ross & Co. obtained a patent for a new form of lens, which they called the " Concentric," from the fact that the internal and external surfaces of each combination were struck from a common centre, as shown in fig. 97. It will be seen that these lenses are practically what would with the old glasses be negative lenses - that is, they are thinner in the middle than at