Objective was passive athermalization.

摘要

The lens has an optical group (G2) whose optical power is a determined sign. The group has an athermalisation lens (21) whose index variation according to temperature is negative and whose optical power sign is identical to the determined sign, where the lens (21) is made of calcium fluoride. A diffractive element (221) ensures an achromatization of the lens. The group includes a main lens (22) whose sign of optical power is identical to the determined sign and whose index variation according to temperature is positive.