The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
Nov. 07, 1978
Filed:
Jan. 24, 1977
Kazuo Tanaka, Tokyo, JP;
Kunio Takeshi, Tokyo, JP;
Canon Kabushiki Kaisha, Tokyo, JP;
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 PRINCIPOINT 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 PRINCIPOINT 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.