Projection lens with infinitely variable focal length - has negative doublet movable between fixed front doublet and rear group, with specified conditions for this group(CS 30.6.80)

摘要

The lens consists of a cemented (R2) doublet (1a,b), as positive front element (I), an axially movable cemented (R5) negative element (II), and a fixed positive four-element (3-6) rear group (III). This group consists of a biconvex lens (3), a cemented (R10) collecting doublet (4), a cemented (R13) dispersing meniscus (5), and a collecting meniscus (6). Conditions are specified for the values of the focal lengths of the three elements (3-5) of the rear group in relation to the overall focal length of this group (III) and that of the front element (I). Structural details are specified for two examples with focal length variable from 35.83 to 71.46 mm and 34.79 to 70.50 mm respectively.