The Dictionary Of Photography

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

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Lens
which was much used and admired. Single lenses were first of all of the kind shown in fig. 75, with which extremely small diaphragms are necessary to reduce spherical aberration. This was improved on by Grubb, and his lens is shown in fig. 80.
Fig. 81.
Fig. 82.
A crown-glass lens of meniscus form is presented to the object, and is cemented to a flint meniscus. This gave a much flatter field, and spherical aberration was much reduced, allow-ing the use of larger diaphragms. Dallmeyer introduced his single lens (fig. 81), which consists of a negative flint enclosed
Fig. 83.
Fig. 84.
between two positive crown-glass lenses. This enabled a much larger aperture to be employed, and eliminated spherical aber-ration. Marginal definition and flatness of field were both improved. To obviate distortion, many doublet lenses were introduced, that of Mr. Ross being shown in fig. 82. This
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