Optical: systems and elements – Lens – With variable magnification
Reexamination Certificate
1999-12-20
2001-12-25
Schwartz, Jordan M. (Department: 2873)
Optical: systems and elements
Lens
With variable magnification
C359S687000
Reexamination Certificate
active
06333823
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a zoom lens system to be used in a compact video camera or digital camera and the like.
2. Description of the Related Art
Generally, in a zoom lens system, it is necessary to maintain a space to allow the lens groups to move for zooming, as a result, the overall length of the zoom lens system tends to be long in comparison with a fixed focus lens system. Accordingly, there is a physical limit in reducing the dimensions of a camera body measured in a direction parallel with the optical axis of a lens system of the camera (hereinafter, the thickness of a camera).
In recent years, development has been made to produce digital cameras with higher resolution, and accordingly a frame size (an image size determined by a lens system) of an image pick-up device, such as a CCD (charge-coupled device), has been increased, and an optical system as well tends to be larger. For Miniaturizing a camera with a zoom lens system, a retractable type camera which is arranged to retract the lens barrel thereof when the main power is turned off is known. However, the mechanism of this retractable type camera is complicated, and is disadvantageous in regard to costs.
SUMMARY OF THE INVENTION
It is an object of the present invention to miniaturize a camera having a zoom lens system, in particular, to reduce the thickness of the camera.
In the present invention, the optical axis of a zoom lens system is deflected by a deflector (e.g., a mirror or a prism) in order reduce the thickness of the camera. Further, in the present invention, the deflector is selectively positioned in the zoom lens system.
In order to achieve the above mentioned object, there is provided a zoom lens system including a plurality of lens groups, and a deflector, being provided between lens groups which are made moveable upon zooming, for deflecting the optical axis of the zoom lens system.
The plurality of the lens groups preferably includes a positive first lens group, a negative second lens group, and a positive third lens group, in this order from the object. The zoom lens system is arranged to perform zooming by moving the second and third lens groups along the optical axis of the zoom lens system, and the deflector is positioned between the second and third lens groups.
The zoom lens system further includes a fourth lens group being provided on the image side of the positive third lens group.
In order to enhance the optical performance of the three-lens-group zoom lens system, the following conditions are preferably satisfied:
0.2<log
10
Z
a
/log
10
Z<0.4 (1)
0.2<f
w
/f
3
<0.6 (2)
−1.3<m
3t
<−0.8 (3)
wherein
Z2=M
2t
/m
2w
Z=f
t
/f
w
m
2t
designates the transverse magnification of the second lens group at the long focal length extremity;
m
2w
designates the transverse magnification of the second lens group at the short focal length extremity;
f
t
designates the focal length of the entire lens system at the long focal length extremity;
f
w
designates the focal length of the entire lens system at the short focal length extremity;
f
3
designates the focal length of the third lens group; and
m
3t
designates the transverse magnification of the third lens group at the long focal length extremity.
In order to enhance the optical performance of the four-lens-group zoom lens system, the following conditions are preferably satisfied:
0<log
10
Z
2
/log
10
Z<0.4 (1)
0.2<f
w
/f
(3-4)w
<0.6 (2)
−1.3<m
3t
<−0.8 (3)
wherein
Z
2
=m
2t
/m
2w
Z=f
e
/f
w
m
2t
designates the transverse magnification of the second lens group at the long focal length extremity;
m
2w
designates the transverse magnification of the second lens group at the short focal length extremity;
f
t
designates the focal length of the entire lens system at the long focal length extremity;
f
w
designates the focal length of the entire lens system at the short focal length extremity;
f
(3-4)w
designates the resultant focal length of the third lens group and the fourth lens group at short focal length extremity; and
m
3t
designates the transverse magnification of the third lens group at the long focal length extremity.
In the zoom lens system, the deflector is preferably a mirror.
In order to suitably position the mirror, the zoom lens system preferably satisfies the following condition:
0.25<DM
min
/f
t
<0.8 (4)
wherein
DM
min
−DMa+DMb
DMa designates the minimum distance from the lens group immdiately before the mirror to the center of the mirror which is defined as the intersecting point where the optical axis meets the reflection surface of the mirror;
DMb designates the minimum distance from the center of the mirror to the lens group immediately behind the mirror; and
f
t
designates the focal length of the entire lens system at the long focal length extremity.
In the zoom lens system, the deflector is preferably a prism.
In order to suitably position the prism, the zoom lens system preferably satisfies the following condition:
0.8<DP
min
/2y<1.5 (5)
wherein
DP
min
=DPa+(Lp/Np)+DPb
DPa designates the minimum distance from the lens group immediately before the prism to the prism;
Lp designates the axial thickness of the prism along the optical axis;
Np designates the refractive index of the prism;
DPb designates the minimum distance from the prism to the lens group immediately behind the prism; and
2y designates the image size determined by the optical system (y=f×tan W; f: the focal length of the entire lens system; W: the half angle-of-view).
Further, the zoom lens system preferably satisfies the following condition:
0.25<DP
min
f
t
<0.8 (6)
wherein
f
t
designates the focal length of the entire lens system at the long focal length extremity.
The present disclosure relates to subject matters contained in Japanese Patent Application No. Hei-10-365721 (filed on Dec. 22, 1998) and Japanese Patent Application No. Hei-10-365722 (filed on Dec. 22, 1998) which are expressly incorporated herein by reference in their entirety.
REFERENCES:
patent: 3357775 (1967-12-01), Appeldorn et al.
patent: 4249793 (1981-02-01), Uehara
patent: 5442484 (1995-08-01), Shikawa
patent: 6072637 (2000-06-01), Okada et al.
patent: 10-20191 (1998-01-01), None
Ito Takayuki
Ozaki Hiroyasu
Asahi Kogaku Kogyo Kabushiki Kaisha
Greenblum & Bernstein P.L.C.
Schwartz Jordan M.
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