Early wide-angle lenses were often derived from standard 50mm lenses. Biogon designed for Contax at Zeiss was derived from Sonnar. Because it was for rangefinder camera. Therefore the back focus is very small.
Split Triple
Splitting an element into two elements allows the aberrations of the two to be substantially reduced from that of the original element. In the Cooke triplet, the outer crowns (rear) are often split in order to reduce the zonal spherical aberration and to thus allow the speed of the lens to be increased. Note that, as the speed is increased, the angular field coverage is reduced. The split rear-crown form is often used in camera lenses for 8mm, 16mm, small format TV, and CCD cameras, typically at the speed of about f/2.
Double-Guass (Biotar)
The Biotar or double-Guass type is a descendant of the double-meniscus anastigmat lenses. One of the many variants of the double-meniscus form consisted of outer positive singlets and inner connected 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. A departure from symmetry allowed the speed of the lens to be increased to f/2, and a tremendously useful and powerful design form was born. It can be made into a moderately wide-angle lens, an enlarger lens, a high-resolution objective, or a lens of extremely high speed.
The basic six-element version with the positive front element is meniscus in shape, usually of a lanthanum flint glass with an index of about 1.7 and a V value of about 48. The second element tends to be meniscus, although a plano-convex or a mild biconvex form is not unusual; its index is typically a bit lower and its V value higher than the first element. The third element usually has an index close to that of the second element, and it is a dense flint from along the glass line. The fourth element is usually biconcave and made of a glass-line flint with a slightly higher index than the third element. The fifth and sixth elements are ordinarily both biconvex and of lanthanum flint glass.
Splitting the rear singlet (seven-element) of the Biotar is an excellent way to improve on the basic configuration. It is a commonly used technique to allow an increased speed, and is often seen in faster 35mm camera lenses. For eight-element Biotar, both outer elements are split and the capability for a reasonable state of correction is achieved using only medium-high-index glass.
Double-Guass (planar)
The first double-Guass lenses were quite thin, but in 1896, Paul Rudolph described the Zeiss planar, which used thick meniscus components, with an aperture of f/4.5. The planar also uses buried surfaces, in which there is a difference of dispersion (to correct chromatic aberration) but no significant difference in refractive index. Although it is not desirable in itself, it does provide a simple way of correcting chromatic aberration without affecting the monochromatic aberrations. The planar was not immediately developed into a high-aperture lens. H.W.Lee of Taylor Hobson designed the first high-aperture double-Guass in 1920. This lens has near front-back symmetry. It uses much thicker meniscus components, which are helpful in reducing the Petzval sum and the oblique spherical aberration. At f/2 it has aberrations that are not much worse than the planar at f/4.
These lenses performed very well as normal and medium-long focus lenses for small and medium format cameras. A classic Planar design is the 105mm f2.5 Nikkor produced from 1971 to 2006.
Lenses for compact point-and-shoot camera
Modern compact 35mm cameras use lenses with focal length of 35mm. It is basically a triplet with a meniscus field flattener.
