Patent US4726668A successfully refreshed from Google Patents.
US4726668A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Zoom lens of short total length
Assignee: Canon Inc
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Filing: 1985-06-05
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Granted: 1988-02-23
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Expires: 2005-06-05
Abstract
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.
Inventors
- 👤 Hiroki Nakayama
- 👤 Yasuhisa Sato
- 👤 Kouji Oizumi
- 👤 Yasuyuki Yamada
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-07 19:44
CPC Classifications
G; G02; G02B; G02B15/00; G02B15/14; G02B15/142
Claims Analysis
Total Claims: 14
Claim 1
Independent Claim
113 words
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 (β2) of said middle lens unit and a lateral magnification (β3) of said rear lens unit increase continuously as the focal length increases.
Claim 2
Dependent Claim
113 words
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 (β2) of said middle lens unit and a lateral magnification (β3) of said rear lens unit increase continuously as the focal length increases.
Claim 3
Dependent Claim
20 words
A zoom lens according to claim 1, wherein both of said lateral magnifications vary within such ranges as to satisfy:
Claim 4
Dependent Claim
34 words
0<β2T/β2W<1.5 1.0<β3T/β3W<1.7 wherein β2W and β2T are the lateral magnifications of said middle lens unit for the minimum and maximum focal lengths respectively, and β3W and β3T are those of said rear lens unit.
Claim 5
Dependent Claim
34 words
0<β2T/β2W<1.5 1.0<β3T/β3W<1.7 wherein β2W and β2T are the lateral magnifications of said middle lens unit for the minimum and maximum focal lengths respectively, and β3W and β3T are those of said rear lens unit.
Claim 6
Dependent Claim
124 words
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 ψ 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.
Claim 7
Dependent Claim
124 words
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 ψ 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.
Claim 8
Dependent Claim
29 words
A zoom lens according to claim 3, satisfying the following condition: 1.2<φT/φW<4.0 wherein φW and φT are the overall refractive powers for the minimum and maximum focal lengths respectively.
Claim 9
Dependent Claim
166 words
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.
Claim 10
Dependent Claim
166 words
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.
Claim 11
Dependent Claim
23 words
A zoom lens according to claim 5, satisfying the following condition: 0.5fW<f2<6fW wherein f2 is the focal length of said middle lens unit.
Claim 12
Dependent Claim
48 words
A zoom lens according to claim 5, satisfying the following conditions: 0.5fW<R11<fW -0.6fW<R31 <-0.2fW wherein R11 is a radius of curvature of a frontmost lens surface of said front lens unit and R31 is a radius of curvature of a frontmost lens surface of said rear lens unit.
Claim 13
Dependent Claim
21 words
A zoom lens according to claim 5, wherein said rear lens unit consists of a negative meniscus lens of rearward convexity.
Claim 14
Dependent Claim
24 words
A zoom lens according to claim 5, wherein said middle lens unit includes a negative lens and a positive lens independent of each other.
References Cited (Backward Citations)
US4494828A
Cited
US4506958A
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1991-02-22 | 1991-08-24 | 1992-02-23 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1995-02-22 | 1995-08-24 | 1996-02-23 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1999-02-22 | 1999-08-24 | 2000-02-23 | $7700.00 | Window Closed / Lapsed |