Telephoto lens

A photographic lens of substantially constant equivalent focal length adapted to be mounted to a camera which includes an image frame, said lens having an equivalent focal length when focused to infinity greater than its front vertex distance, a lens housing, a plurality of lens elements defining a positive objective coaxially mounted in said housing, means for moving said objective axially to focus said lens, a compensating lens for correcting off-axis imagery when said lens is close focused in said housing behind said objective in fixed relation to said housing, said compensating lens being of negative power and acting to slightly decrease the equivalent focal length of the overall lens as said objective is moved forward thereof for close focusing, the equivalent focal length of said compensating lens being no greater than three times the equivalent focal length of the overall lens.

A lens of predetermined essentially fixed equivalent focal length, said equivalent focal length being at least 2.5 times the diagonal of the image frame of a camera adapted to mount said lens, said lens having an equivalent focal length when focused at infinity greater than its front vertex distance, said lens comprising a housing adapted to be mounted to a camera body, a plurality of lens elements coaxially mounted in said housing, means for moving said plurality of element in fixed relation for focusing of said lens, a rear compensating lens fixed in said housing for enabling close focusing of the overall lens with minimal aberrations, said compensating lens being of negative power and comprising a meniscus with the concave surface thereof facing the image plane, the equivalent focal length of said compensating lens being no greater than three times the equivalent focal length of the overall lens.

A lens having an equivalent focal length greater than its front vertex distance when focused to infinity comprising a housing adapted to be mounted to a camera, a plurality of lens elements coaxially mounted in said housing and movable axially in fixed relation for focusing of said lens, a corrector lens in said housing behind said plurality and in fixed relation to said housing, said plurality of lens elements defining a first group of positive power, a second group of negative power followed by an aperture stop, and a third positive group, said lens having an equivalent focal length at least two and one-half times the diagonal of the image frame of a camera to which it may be mounted, said fixed lens being of negative power having an equivalent focal length no greater than three times the equivalent focal length of the overall lens, said fixed lens serving to correct for aberrations due to off-axis imagery when said lens is close focused.

A lens defined substantially by the following data as scaled for a 24.times.36mm image frame and an equivalent focal length of 135mm:

• Axial Distance Lens Radius Between Surfaces N.sub.d V.sub.d ______________________________________ R1 51.237mm L1 12.918mm 1.623 56.9 R2 759.41 3.977 R3 40.464 L2 8.653 1.498 65.1 R4 103.150 3.806 R5 -317.56 L3 4.000 1.805 25.5 R6 36.719 23.467 R7 101.995 L4 6.936 1.699 30.1 R8 -64.646 15.544 R9 -41.418 L5 2.800 1.806 40.7 R10 -645.29 1.0 - 18.321 R11 -187.767 L6 3.400 1.596 39.2 R12 -96.478 40.485 ______________________________________
• Where N.sub.d is the index of refraction, V.sub.d is the Abbe number, L1-L6 represent lens elements progressively from the front element to the rearmost element, R1-R12 are the radii of the lens surfaces, the axial distance is measured axially between lens surfaces;
• and the last axial distance is the back focal length of the lens.