The Dictionary Of Photography

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

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the margins ; but by the use of particular kinds of Jena glass the manufacture of such combinations with a positive focus was rendered possible. The advantage of these lenses lies in the fact that they are free from chromatic aberration and astigmatism ; and a iens the focus of which is one-third less than the longer
//19. Some
base line of the plate covers that plate sharply with
//16, and at this aperture they
of the lenses are made to work at
give a uniform softness of definition, arising from spherical aberration. The only disadvantage is that focussing must be done with the aperture which is to be used for exposing. These lenses possess a flatness of field which is very remark-
Fig. 98.
able. Zeiss of Jena has introduced several new forms of lenses, all constructed of Jena glass, and possessing a freedom from astigmatism and chromatic aberration quite remarkable. Among the recent introductions of Mr. Dallmeyer may be mentioned the telephotographic lens, which is an adaptation ot the principle of the Galilean telescope, so that a short camera may be used with what is virtually a lens of long focus ; a new power being thus placed in the hands of the tourist wishing to secure a large rendering of distant objects - architectural detail for instance. (See Adon ; also Animals, Photographing.) A special negative lens, corrected for colour and correspond-ing to the concave eye-piece of the Galilean telescope, is set at a determinate distance between an ordinary objective