Seven-lens zoom objective with axially movable second lens - has lenses specified for good correction of spherical and coma aberration

摘要

The zoom objective comprises at least six lenses (L1-7) separated by air spaces (l1-6). The front lens (L1) is a rearwardly convex (r2) dispersing lens whilst the bi-convex second lens (L2) is axially movable. The collecting fifth lens (L5) is strongly forwardly convex (r9) whilst the dispersing sixth lens (L6) is strongly rearwardly concave (r12) and is followed by a collecting rear lens (L7). The collecting third lens (L3) is immediately followed by a lens (L4) with low dispersing power whilst the air space (l3) between these two lenses (L3,4) forms a thin air lens with greater central than peripheral thickness. Limits are specified for certain parameters and curvature radii (r), lens thicknesses (d), air spaces (l), refractive indices and Abbe-numbers listed in the description for two examples with focal lengths variable between 33.3 and approx. 62.