Optical: systems and elements – Lens – With reflecting element
Reexamination Certificate
1997-12-29
2001-01-23
Epps, Georgia (Department: 2873)
Optical: systems and elements
Lens
With reflecting element
C359S631000, C359S633000, C359S728000
Reexamination Certificate
active
06178052
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to a finder optical system comprising an image inversion optical subsystem, and more particularly to a finder optical system for viewing an image of an object inverted by an objective in the form of an erected image using an image inversion optical subsystem.
Typical finder optical systems are known from U.S. Pat. Nos. 3,810,221 and 3,836,931, JP-A's 59-084201, 62-144127, 62-205547, 1-257834 (corresponding to U.S. Pat. No. 5,274,406), 8-201912, 8-234137, 8-248481, 8-292368, 8-292371 and 8-292372, and EP 0722106A2.
These prior art systems include a single image formation type real image finder optical system used on cameras or video cameras, which makes use of an image inversion optical subsystem comprising an elaborately combined mirror and prism arrangement for the observation of an erected image. This optical system is not only designed to erect an inverted image of an object by use of a combined mirror and prism, but is also designed to achieve size reductions by using a turn-back optical path. Since the reflecting surfaces of the mirror and prism in the image inversion optical subsystem are decentered with respect to the optical axis, however, rotationally asymmetric decentration aberrations are produced when the reflecting surfaces have powers. The resulting optical performance loss can never be prevented only by use of a rotationally symmetric lens. For this reason, optical elements such as mirrors and prisms in image inversion optical subsystems are generally in plano surface forms.
To meet recently increasing demands for size reductions of cameras and video cameras, it is now required to achieve further size reductions of finder optical systems used on them. To this end, various investigations are made of the direction and angle of the reflecting surfaces of mirror and prism elements in image inversion optical subsystems or combinations of such optical elements. However, any drastic solution to this problem cannot be obtained because such reflecting surfaces are still used in plano surface forms.
SUMMARY OF THE INVENTION
In view of such problems associated with the prior art, it is an object of the invention to provide a compact yet high-performance finder optical system which enables decentration aberrations to be corrected by means of a rotationally asymmetric surface.
According to one aspect of the invention, the aforesaid object is achieved by the provision of an image inversion optical subsystem comprising a reflecting optical element incapable of image inversion, wherein a rotationally asymmetric surface is provided at an optical surface of said reflecting optical element. According to another aspect of the invention, there is provided an image inversion optical subsystem comprising an image inversion optical element having image inversion action (at least on vertical inversion of an image or horizontal inversion of an image), wherein a rotationally asymmetric surface is provided at an optical surface of said optical element.
By the term “rotationally asymmetric surface” used herein is intended every surface having a rotationally asymmetric surface shape. Therefore, it is understood that the term “rotationally asymmetric surface” includes an optical surface with an axis of rotational symmetry designed to be located outside of the surface. However, it is understood that the rotationally asymmetric surface does not include a surface with an axis of rotational symmetry located inside and at a position off the center thereof, because a part of surface shape is of rotational symmetry. Surface shape is passed on defined for an area (effective area) of a physically optical surface through which light beams pass rather than on a non-effective area thereof through which only ghost or flare light passes. In this regard, however, the rotationally asymmetric surface with a section in both the X- and Y-axis directions taking a curved surface (line) shape is understood to refer to a toric or other surface, except a cylindrical surface with a sectional shape in one direction taking a plano surface (straight line) form.
The term “rotationally asymmetric surface having no axis of rotational symmetry both inside and outside” is understood to refer to a surface free of rotational symmetry at design stages such as an anamorphic surface, except a rotationally asymmetric surface having an axis of rotational symmetry outside such as a toric or cylindrical surface. The term “rotationally asymmetric surface” used herein is also understood to include a surface having two surfaces symmetric with respect to a plane (the surfaces may be called axially symmetric surfaces in two-dimensional planes but cannot be expressed in terms of axial symmetry, because surfaces include curved surfaces in addition to plano surfaces), a free form surface symmetric with respect to a plane (TFC surface for short) having only one surface symmetric with respect to plane, and an asymmetric polynomial surface (APS surface for short).
As one example, the rotationally asymmetric surface is defined by the following polynomial (a):
Z
=
C
2
+
C
3
y
+
C
4
x
+
C
5
y
2
+
C
6
yx
+
C
7
x
2
+
C
8
y
3
+
C
9
y
2
x
+
C
10
yx
2
+
C
11
x
3
+
C
12
y
4
+
C
13
y
3
x
+
C
14
y
2
x
2
+
C
15
yx
3
+
C
16
x
4
+
C
17
y
5
+
C
18
y
4
x
+
C
19
y
3
x
2
+
C
20
y
2
x
3
+
C
21
yx
4
+
C
22
x
5
+
C
23
y
6
+
C
24
y
5
x
+
C
25
y
4
x
2
+
C
26
y
3
x
3
+
C
27
y
2
x
4
+
C
28
yx
5
+
C
29
x
6
+
C
30
y
7
+
C
31
y
6
x
+
C
32
y
5
x
2
+
C
33
y
4
x
3
+
C
34
y
3
x
4
+
C
35
y
2
x
5
+
C
36
yx
6
+
C
37
x
7
(
a
)
In general, the surface defined by the above polynomial (a) has no symmetric surface with respect to both the x-z axis and the y-z axis. If, for instance, all the odd number terms with respect to x are reduced to zero, it is then possible to obtain a TFC surface wherein there is only one symmetric surface parallel with the y-z surface. As one example, this may be achieved by reducing the coefficients of terms C
4
, C
6
, C
9
, C
11
, C
13
, C
15
, C
18
, C
20
, C
22
, C
24
, C
26
, C
28
, C
31
, C
33
, C
35
and C
37
. . . .
If the odd number terms with respect to y are all reduced to zero, it is also possible to obtain a TFC surface wherein there is only one symmetric surface parallel with the x-z surface. As one example, this may be achieved by reducing the coefficients of terms C
3
, C
6
, C
8
, C
10
, C
13
, C
15
, C
17
, C
19
, C
21
, C
24
, C
26
, C
28
, C
30
, C
32
, C
34
and C
36
. . . . Productivity is improved by the symmetric surface.
It is more preferable to use an APS surface having no symmetric surface at all. This is because there is an increase in the degree of freedom in designing a compact surface while making as good correction for aberrations as possible.
The above defining polynomial is given as one example. As mentioned above, the major feature of the invention is to make correction for rotationally asymmetric decentration aberrations produced at a rotationally asymmetric surface. It is thus understood that all other polynomials defining the rotationally asymmetric surface hold for the invention.
For instance, the rotationally asymmetric surface may be defined by Zernike's polynomial. That is, the shape of this surface may be defined by the following polynomial (b) with the Z-axis being an axis in Zernike's polynomial. The rotationally asymmetric surface is defined by polar coordinates for the height of the Z-axis with respect to the X-Y surface. Here A is a distance from the Z-axis in the X-Y surface, and R is an angle of azimuth around the Z-axis as represented by an angle of rotation measured from the Z-axis.
X
=
R
×
cos
(
A
)
Y
=
R
×
sin
(
A
)
Z
=
Aoki Norihiko
Togino Takayoshi
Epps Georgia
Olympus Optical Co,. Ltd.
Pillsbury Madison & Sutro LLP
Schwartz Jordan M.
LandOfFree
Finder optical system does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Finder optical system, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Finder optical system will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2527621