Thermal insulation for heat sensitive lens elements

Details Thermal insulation for heat sensitive lens elements Thermal insulation for heat sensitive lens elements

1985-07-22

1987-05-26

Punter, William H.

350580, G02B 702, G02B 2316

Patent

active

046680489

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. By using these features, it becomes practical to dispense with a heat reflecting coating on the outer surface of the housing, sometimes used when a sensitive optical element needs to be protected from heat of the sun's rays, such an external coating being undesirable because it makes the lens conspicuous and therefore unsuitable for some kinds of photography. Using the special heat-impeding features of this invention, the outer surface of the housing can be black and inconspicuous, even though the black surface absorbs more heat from the rays of the sun than a lighter colored heat reflective surface.

REFERENCES:
patent: 1540781 (1925-06-01), Keuffel
patent: 1791254 (1931-02-01), Brockdorff
patent: 2376710 (1945-05-01), Maurer
patent: 3553604 (1971-01-01), Andress et al.
patent: 3609236 (1971-09-01), Heilman
patent: 4534624 (1985-08-01), Toda et al.

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