The theoretical performances of several f/1.5 triplet lenses suitable for use in the 3 to 5um spectral region are compared. Examples are given in which all the materials used have a finite visible transmittance. As centering errors can thus be considerably reduced, it is expected that such a lens will in practice approach more closely its theoretical performance. These lenses are also considerably less sensitive to manufacturing tolerances as a result of lower index materials, and the use of low dn/dT materials offers other advantages over the more usual silicon-germanium combination.
M. W. McDowell,
H. W. Klee,
"Achromatization In The 3 To 5µm Spectral Region With Visible Light Transmitting Materials," Optical Engineering 23(2), 232187 (1 April 1984). https://doi.org/10.1117/12.7973409