Modern Lens Design, 2nd Edition

Chapter 12The Biotar or Double-Gauss Lens

12.1 The Basic Six-Element Version

The Biotar or double-Gauss type is a descendant of the double-meniscus anastigmat lenses discussed in Chap. 11. One of the many variants of the double-meniscus form consisted of outer positive singlets and inner cemented meniscus negative doublets, in a symmetrical construction. These lenses had the speed and angular coverage typical of their genre, i.e., good angular coverage at a quite modest aperture; however, a departure from symmetry allowed the speed of the lens to be increased (initially) to f/2, and a tremendously useful and powerful design form was born.

This design type is the basis of most normal-focal-length, 35-mm camera lenses, having supplanted the Sonnar ...