Apparatus for preventing internal reflection in zoom lens

Claim 1

A lens system having means for preventing undesired light beams from reaching a focal plane, said lens system comprising: a rear securing plate; a first and a second guide post perpendicularly secured to said rear securing plate; an antireflection wall that is freely and slidably supported by said first guide post; a first roller, said first roller being mounted on the circumference of said antireflection wall such that said first roller is substantially perpendicular to the optical axis of said lens system; a rear lens, said rear lens being freely and slidably supported by said first guide post, said rear lens being located forward of said antireflection wall; a second roller, said second roller being mounted on the circumference of said rear lens such that said second roller is substantially perpendicular to the optical axis of said lens system; a lens barrel, said lens barrel being freely and slidably supported by said second guide post and having a third roller mounted thereon, said lens barrel being spaced forward of said rear lens a predetermined distance and having an aperture through its center substantially perpendicular to its circumference for accepting a front lens, said front lens being rotatable in said lens barrel; a cam ring having a first and second cam groove, said cam ring being positioned around said first and second guide posts, said antireflection wall, said rear lens and said lens barrel such that one end of said cam ring is proximate said rear securing plate, said first and second rollers engaging said first cam groove in said cam ring and said third roller, engaging said second cam groove in said cam ring, said cam ring being rotatable about the optical axis of said lens system relative to said rear securing plate so as to cause a sliding of said lens barrel, said rear lens and said antireflection wall on said guide posts in response to each roller following a predetermined path determined by the shape of said cam grooves, the shape of said first cam groove being selected so as to position said antireflection wall at a point along the optical axis of said lens system to intercept said undesired light beams that exit from said rear lens; a front securing plate, said front securing plate being positioned proximate the other end of said cam ring that is proximate said lens barrel, said guide posts being secured to said front securing plate; and means for rotatably moving said front lens mounted in said lens barrel.