Abstract: A long focal length or telephoto lens for photographic purposes has an optical element with a high coefficient of thermal expansion, and special features to impede transmission of heat to this element when the housing of the lens becomes heated by rays of the sun. A thermal insulation bridge, preferably of ceramic material, is interposed in the heat flow path from the rear part of the housing to the lens tube which contains the sensitive optical element. Moreover, this lens tube is spaced inwardly a substantial distance from the surrounding front part of the housing, to provide a substantial air space between tube and housing, with air inlet and outlet openings for circulation of air. The outer surface of the lens tube has a heat reflective coating, to reflect rather than absorb heat radiated inwardly from the surrounding housing when the housing becomes heated by rays of the sun.