A zoom lens assembly ( 10 ) compensates optically, as opposed to mechanically, for changes in temperature. In a preferred embodiment a difference in focus between WFOV and NFOV zoom lens positions, over temperature, is minimized such that any actual shift in focus falls within the depth of focus of the zoom lens assembly. The zoom lens assembly has, along an optical axis, first and third lens elements ( 12,16 ) that are made from a first material and that have a positive power, a second lens element ( 14 ) interposed between the first and third lens elements and movable along the optical axis between a WFOV and NFOV position. The second lens element has a negative power and is made of a second material. The materials are selected such that a change in refractive index for a change in temperature of the first material is less than a change in refractive index for a change in temperature of the second material. The zoom lens assembly also color corrects incident radiation using a diffractive surface on at least one of the first and third lens elements.
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