GB851170A - Lens system for a photographic objective - Google Patents

Abstract

851,170. Interchangeable lens systems. ZEISSSIIFTUNG, C., [trading as ZEISS, C. [firm of]]. Sept. 22, 1958 [Sept. 25, 1957], No. 30157/58. Class 97(1) An interchangeable lens system which can be exchanged for the two components in front of the diaphragm of a 4-component photographic objective so as to provide a new objective which has the same back focal length as, but a longer equivalent focal length than, the basic objective, is characterised in-that- (a) it contains an air space the limiting surfaces of which are both concave towards the diaphragm, (b) the algebraic sum of the refractive powers of two said surfaces has a negative value, (c) the algebraic sum of the refractive powers of all the surfaces in front of said air space has a negative value, (d) the part of the system lying in front of the air space has negative focal length, (e) the algebraic sum of the refractive powers of the surfaces between the air space and the diaphragm has a positive value, and (f) the apical separation between the surface limiting the air space on the object side and the diaphragm is between 0À02 f and 0À35 f, where f is the focal length of the new objective. The front lens of the system is preferably a meniscus negative lens concave towards the diaphragm, and made of glass with an Abbe number less than 35. Optical data are given in the Specification for one form of a 4-component basic objective, and for two forms of a lens system which can be substituted for the front two components of this basic objective. One lens system is as shown made up of compenents LI -LVI, the components LVII-LIX being the remaining components of the basic objective.