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US 4,726,668 AGranted
Zoom lens of short total length
AssigneeCanon Kabushiki Kaisha
InventorsHiroki Nakayama, Yasuhisa Sato, Kouji Oizumi, Yasuyuki Yamada
Life of this patent
Estimating the term…
Abstract
In the disclosed zoom lens, a positive front lens unit and a negative rear lens unit are moved forwardly axially in differential relation to vary the overall focal length from a minimum to a maximum value, while a positive middle lens unit is kept stationary during the variation of the focal length. A diaphragm determining the F-number is positioned at a fixed point between the front and rear lens units.
Claims9
A zoom lens comprising:
- a front lens unit of positive refractive power;
- a middle lens unit of positive refractive power arranged on an image side of said front lens unit;
- and
- a rear lens unit of negative refractive power arranged on the image side of said middle lens unit, said front lens unit and said rear lens unit being simultaneously movable forward along an optical axis while said middle lens unit is held stationary to vary an overall focal length from a minimum to a maximum, wherein a lateral magnification (.beta.2) of said middle lens unit and a lateral magnification (.beta.3) of said rear lens unit increase continuously as the focal length increases.
1 more element
A zoom lens comprising:
- a front lens unit of positive refractive power;
- a middle lens unit of positive refractive power arranged on an image side of said front lens unit;
- and
- a rear lens unit of negative refractive power arranged on the image side of said middle lens unit, said front lens unit and said rear lens unit being simultaneously movable forward along an optical axis while said middle lens unit is held stationary to vary an overall focal length from a minimum to a maximum, wherein an overall refractive power .psi. of said middle lens unit and said rear lens unit always takes a negative value despite variation of the focal length, and the negative value increases as the focal length becomes longer.
1 more element
A zoom lens comprising:
- a front lens unit of positive refractive power;
- a middle lens unit of positive refractive power arranged on an image side of said front lens unit;
- and
- a rear lens unit of negative refractive power arranged on the image side of said middle lens unit, said front lens unit and said rear lens unit being simultaneously movable forward along an optical axis while said middle lens unit is held stationary to vary an overall focal length from a minimum to a maximum, in which said zoom lens satisfies the following conditions:
- ##EQU3## wherein f1 and f3 are focal lengths of said front and said rear lens units, respectively, fW is the maximum overall focal length, e12W is an interval between principal points of said front and said middle lens units when the overall focal length is the minimum, and e23T is an interval between principal points of said middle and said rear lens units when the overall focal length is the maximum.
2 more elements
Dependencies are inferred from the claim text.