Lens assembly having automatic thermal focus adjustment

A projection television lens assembly comprising:

• a generally tubular lens mount having an interior and an exterior and formed from a material having a first coefficient of thermal expansion,
• first and second lenses mounted along an axis within said interior of said lens mount,
• a third lens mounted along said axis, said third lens adapted for mounting adjacent a light source,
• a generally tubular locus mount coupled to said exterior of said lens mount and formed from a material having a second coefficient of thermal expansion different than said first coefficient of thermal expansion, and
• adjustment and locking structure coupling said lens mount to said focus mount, said first and second lenses carried along said axis on one side of said adjustment and locking structure, and said adjustment and locking structure being operative to allow said lens mount to be moved relative to said focus mount along said axis and then locked in position to provide an initial focus position of said first and second lenses relative to said third lens,
• wherein, after at least said first and second lenses have been locked in the initial focus position and the lens mount, focus mount and third lens are heated by the light source, said lens mount and focus mount automatically move relative to each other to thereby move said first and second lenses together relative to said adjustment and locking structure and to said third lens to a new focus position as a result of the differing first and second coefficients of thermal expansion.