Patent
1977-01-24
1978-11-07
Sacher, Paul A.
G02B 1518
Patent
active
041242742
ABSTRACT:
A zoom lens comprising a front lens group, a plurality of movable lens groups and an image forming lens group, the front lens group having three sub-groups. The first sub-group counting from the front has a negative refractive power and is movable for focusing purposes. The intermediate or second sub-group has a positive refractive power and is movable for focusing to the front of the third sub-group which has a positive refractive power and which is stationary during focusing. The front lens group is characterized by fulfilling the following relationships: ##EQU1## WHEREIN F.sub.1 AND F.sub.2 ARE THE FOCAL LENGTHS OF THE FIRST AND SECOND SUB-GROUPS RESPECTIVELY; D IS THE AXIAL SEPARATION BETWEEN THE REAR PRINCIPAL POINT OF THE FIRST SUB-GROUP AND THE FRONT PRINCIPAL POINT OF THE SECOND SUB-GROUP OCCURRING WHEN THE ENTIRE SYSTEM IS FOCUSED FOR OBJECT AT INFINITY; A' IS THE OBJECT DISTANCE MEASURED FROM THE FRONT PRINCIPAL POINT OF THE FIRST SUB-GROUP WHEN THE ENTIRE SYSTEM IS FOCUSED FOR AN OBJECT AT A FINITE DISTANCE; AND S and t are the amounts of movement of the first and second sub-groups resulted during focusing from infinity to a closeup at an object distance a' respectively.
REFERENCES:
patent: 3533679 (1970-10-01), Baluteau
patent: 3549235 (1970-12-01), Macher
patent: 3632188 (1972-01-01), Nakamura
Takeshi Kunio
Tanaka Kazuo
Canon Kabushiki Kaisha
Sacher Paul A.
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