Optical: systems and elements – Lens – With variable magnification
Patent
1989-06-08
1991-10-29
Dzierzynski, Paul M.
Optical: systems and elements
Lens
With variable magnification
359745, G02B 900
Patent
active
050610538
ABSTRACT:
A telephoto zoom lens system featuring a zoom ratio on the order of 3 which uses an inexpensive optical material having a lens refractive index and which is compact in size can be attained. A first lens group I closest to the object side has a positive refractive power. The first lens group I includes a first negative maniscus lens element having a convex surface directed toward the object and a second positive lens element having a convex surface with a large curvature directed toward the object. A second lens group II having a negative refractive power is located on the image side of the first lens group I. A third lens group III having a positive refractive power is located on the image side of second lens group II. Lens group III includes a first lens unit IIIa having a positive refractive power and a second lens unit IIIb having a positive or negative refractive power. Zooming is performed by moving the three lens groups independently of one another along the optical axis. Focusing is performed by moving the first lens groups along the optical axis. Second lens group II preferably includes two negative lens elements and one positive lens element. Lens unit IIIa preferably includes two positive lens elements and one negative lens element while lens unit IIIb preferably includes a positive lens and a negative meniscus lens having a convex surface directed toward the image.
REFERENCES:
patent: 4815829 (1989-03-01), Yamanashi et al.
The Jashin Kogyo, 1988, vol. 12.
Asahi Kogaku Kogyo K.K.
Dzierzynski Paul M.
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