Zoom lens of rear focus type

Details Zoom lens of rear focus type Zoom lens of rear focus type

1993-05-18

1994-11-08

LaRoche, Eugene R.

Optical: systems and elements

Lens

With variable magnification

359686, 359687, 359715, G02B 1514, G02B 1318

Patent

active

053632427

ABSTRACT:
A zoom lens of the rear focus type is disclosed, including, from front to rear, a first lens unit of positive refractive power, a second lens unit of negative refractive power, a third lens unit of positive refractive power and a fourth lens unit of positive refractive power, the second lens unit being moved toward the image side when zooming from the wide-angle end to the telephoto end, while moving the fourth lens unit to compensate for the image shift with zooming, and focusing being performed by moving the fourth lens unit. The third lens unit consists of a positive single lens having an aspheric surface. The fourth lens unit includes a negative first lens and a positive second lens, and at least one of lens surfaces of the the first and second lenses is aspherical. Letting the overall focal length of the third and fourth lens units in the wide-angle end be denoted by f3,4, the focal length of the entire lens system in the wide-angle end is denoted by Fw, the distance from the last lens surface to an image plane which is shortest in an entire zooming range when focusing on an infinitely distant object is denoted by Fb, and the zoom ratio denoted by Z, the following conditions are satisfied: ##EQU1##

REFERENCES:
patent: 4836663 (1989-06-01), Hirakawa
patent: 5009492 (1991-04-01), Hamano
patent: 5221994 (1993-06-01), Nishio
patent: 5235466 (1993-08-01), Ono et al.

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