Objective with lens effective only under water - has specified positive supplementary air lens to compensate for divergence under water (AT 15.1.81)

摘要

The optical system comprises a pancratic objective (1) and a positive supplementary front lens (2). On the side facing this front lens, the objective is provided with a lens (D) which is optically ineffective in air and is intended for underwater use. The supplementary group (2) consists of two positive plano-convex lenses (VL1,2) having facing convex surfaces. When used underwater, and with the objective normally focussed, the air lens contained between these lenses (VL1,2) produces the positive refraction required to compensate for the divergence due to the different refraction between air and water. Structural details are specified for three examples of groups (2) for use in combination with a fully specified objective having eleven elements plus lens (D).