JPH01155313A - Secondary image formation type finder optical system - Google Patents

Abstract

PURPOSE:To observe a finder image of high optical performance by setting the lens constitution and refracting power of each lens group of the optical system which allows an erect real image reformed through a relay lens system, etc., to be observed through an ocular so that specific requirements are met. CONSTITUTION:The lens constitution of each lens group and various optical numerals are set as shown by inequalities I. Here, the focal lengths of ocular lenses are fT, fR, fF, and fE, the refractive indexes of the materials of the negative and positive lenses of the relay lens NN and NP, the Abbe numbers of the materials of the negative and positive lenses of the relay lens nuN and nuP, and the radius of curvature of the cemented surface of the cemented lens of the relay lens RA. Consequently, prescribed overall optical length is obtained and the secondary image formation type finder optical system is obtained which allows a finder image of high optical performance to be observed and suits to an electronic still camera, a video camera, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a secondary imaging type finder optical system, and in particular to a secondary imaging type finder optical system having a predetermined optical total length provided with a dedicated objective lens separate from a photographing lens. The present invention relates to a secondary imaging type finder optical system suitable for still cameras, video cameras, etc.

(Prior Art) Recently, various imaging systems have been proposed for electronic still cameras that magnetically record video information on small floppy disks. Among these, many different types of finder optical systems have been proposed.

The overall shape of the electronic still camera differs greatly from that of conventional cameras using silver halide photoreceptors, depending on how the floppy disk is placed within the camera body.

For example, when a floppy disk is housed in a plane parallel to the optical axis of a photographic lens, it is elongated in the optical axis direction, such as in a recording/playback integrated moving video camera.

The so-called inverted Galilean finder optical system and the primary image-forming real image finder optical system using an erecting image prism, which have traditionally been suitable as external finder optical systems for silver halide cameras, are not suitable for electronic still cameras, etc. The total optical length was too short, which caused the following problems.

In other words, if the eyepiece of the finder optical system is placed near the rear of the camera in order to ensure an eyepoint of sufficient length, the front of the objective lens of the finder optical system will be placed in front of the camera because the overall optical length of the finder optical system is short. It will now be placed in a much more recessed position. Therefore, in order to ensure a viewfinder light flux without vignetting, the aperture on the front of the camera must be made large, and the optical axis of the photographic lens and the optical axis of the viewfinder optical system are separated from each other, increasing finder balax. There were problems such as coming.

On the other hand, secondary imaging type finder optical systems used in conventional video cameras and the like are generally too long in the optical axis direction and are not well suited for, for example, electronic still cameras.

(Problems to be Solved by the Invention) The present invention is a so-called two-focus method in which a finder image formed by an objective lens is further re-imaged by a relay lens system, and an erect normal finder image is observed with an eyepiece. In an image-type finder optical system, by appropriately arranging the lens configuration and refractive power of each lens group, electronic still cameras and electronic still cameras are capable of observing a finder image with a predetermined total optical length and high optical performance. The object of the present invention is to provide a secondary imaging type finder optical system suitable for video cameras and the like.

(Means for solving the problem) The finder image formed on the primary focus plane by an objective lens consisting of two positive lenses arranged with their lens surfaces with strong curvature facing each other, is An erect normal finder image is formed on the secondary focus plane through a relay lens made of bonded cemented lenses and a field lens made of a positive lens with the lens surface with strong curvature facing the object side. When observing a finder image of an erect positive image with an eyepiece consisting of two positive lenses arranged with lens surfaces with strong curvature facing each other, the objective lens,
The focal lengths of the relay lens, field lens, and eyepiece lens are fT, fRlfF, and fE in order, and the refractive index of the material of the negative lens and positive lens of the relay lens is N, respectively.
N, NP, the Atsube numbers of the materials of the negative and positive lenses of the relay lens are respectively υN and νP, and the radius of curvature of the bonded lens surface of the cemented lens of the relay lens is RA, 1.0< fR/fT <1.8 −−−−−(+
)1, 0< fF/fE <1.7 --------
(2) 0, 3< l RA l /f R<0.6 −
---- (3) 0.07< NN-NP -
−−−−−−−−−−(4)25 < shiP−shiN
--------------(5) is to be satisfied.

(Example) FIGS. 1 to 3 are schematic diagrams in which finder optical systems of numerical examples 1 to 3 of the present invention are developed, respectively. In the figure, T is an objective lens, which consists of two positive lenses arranged with their lens surfaces with strong curvature facing each other. R is a relay lens, which is made of a cemented lens made by bonding a negative lens and a positive lens. F is a field lens, which consists of one positive lens with a convex surface facing the object side. Reference numeral E denotes an eyepiece, which consists of two positive lenses arranged with their lens surfaces with strong curvature facing each other.

The secondary imaging type finder optical system in this embodiment first focuses a first finder image formed on a first focus plane P by an objective lens T through a relay lens R and a field lens F.
As a result, a second finder image of an erect normal image is formed on the second focus plane Q. A second finder image of an erect image formed on the secondary focus plane Q is then observed through the eyepiece E.

In such a configuration, by setting the lens configuration and optical word value of each lens group as in the above-mentioned conditional expressions (1) to (5), it is possible to observe a finder image with high optical performance.

In particular, the lens configuration of the relay lens is determined by conditional expressions (3) to (5).
By constructing the lens E to satisfy the following, and by constructing the lens E with two positive lenses facing each other with lens surfaces with strong curvature, each lens group itself can suppress various aberrations well. A well-balanced aberration correction is achieved by canceling each other out.

Next, the technical meaning of each of the above conditional expressions will be explained.

Conditional expression (1) relates to the refractive power arrangement of the relay lens and objective lens, which is most important in the present invention. Now, if the focal length of the photographing lens and the viewfinder field of view are constant, the viewfinder magnification can be increased as the combined focal length fT of the objective lens becomes larger. It becomes difficult to correct aberrations in a secondary imaging system consisting of a field lens and a field lens. On the other hand, the total optical length of the secondary imaging system is the shortest at approximately 4fR when the imaging magnification is equal to 1x, and the shorter the focal length of the relay lens, the more advantageous it is in shortening the total optical length, but it is difficult to correct aberrations. It becomes difficult.

Considering the above reasons, in the present invention, the ratio of the focal path @fR/fT of the objective lens and the relay lens is determined by the conditional expression (
1) is set to satisfy.

If the lower limit of conditional expression (1) is exceeded, it is advantageous in shortening the finder magnification and the total optical length, but it becomes difficult to correct the Petzval image plane, while on the other hand, if the upper limit is exceeded, it is advantageous in correcting aberrations. However, the total optical length becomes longer, which is not preferable.

Conditional expression (2) is mainly used to reduce the diameter of the relay lens, and in the present invention, the off-axis pupil light flux passing through the center of the observation pupil is
The focal lengths of the field lens and eyepiece are set so that the beam passes approximately through the center of the relay lens. As a result, even if the refractive power of the relay lens is strengthened, it is possible to avoid a light beam that is sharply refracted around the lens, thereby ensuring good performance across the entire viewing pupil.

When the upper limit of conditional expression (2) is exceeded, the diameter of the relay lens becomes larger and the diameter of the eyepiece lens also becomes larger. Conversely, when the lower limit of conditional expression (2) is exceeded, the diameter of the relay lens becomes larger and the diameter of the field lens increases. It becomes impossible to correct the field curvature that occurs.

Conditional expression (3) relates to the radius of curvature of the cemented lens surface of the relay lens; if the upper limit is exceeded, it becomes difficult to correct field curvature, and conversely, if the lower limit is exceeded, spherical aberration on the secondary imaging surface is corrected. becomes excessive.

Conditional expressions (4) and (5) are related to the refractive index and Atsube number of the glass materials of the negative and positive lenses that make up the relay lens, and conditional expression (4) is mainly concerned with the refraction that can satisfactorily correct field curvature. Regarding the index difference, conditional expression (5) mainly relates to the Abbe number difference for correcting longitudinal chromatic aberration.

If conditional expression (4) is not satisfied, the curvature of field toward the periphery of the screen becomes large, and if conditional expression (5) is not satisfied, chromatic aberration increases, and in both cases it becomes difficult to obtain a good finder image.

Incidentally, in this embodiment, any single lens among the single lenses constituting the objective lens, foot lens, and eyepiece lens may be composed of a cemented lens made by bonding a positive lens and a negative lens. . According to this, it is possible to achieve a finder optical system having high optical performance in which various aberrations such as chromatic aberration are better corrected.

Although the embodiments shown in FIGS. 1 to 3 show the case where each optical element is expanded, a mirror or the like may be arranged between each optical element to bend the optical path.

Next, numerical examples of the present invention will be shown. In numerical examples R
i is the radius of curvature of the first lens surface from the object side, D
i is the i-th lens thickness and air distance from the object side, Ni
and vi are the refractive index and Abbe number of the glass of the i-th lens, respectively, in order from the object side.

Furthermore, Table 1 shows the relationship between each of the above-mentioned conditional expressions and the word values in the numerical examples.

Numerical Example 1 Exit pupil diameter φ3 Maximum exit angle tanθ= 0.17
R1-33,14D 1m2.00 N 1=1.4
9171 v ]-57,4R2--9,63D 2
-9.43 R3-7,79D 3-4.28 N 2-1.49
17112-57.4R4-ω D 4嘗31.
40 R5-25,8505-0,72N 3-1.8466
6shi 3ba 23.9R6= 7.24 06-2.43
N 4=1.77250 v 4-49.6R7-
-22,4407-29,00 R8= 10.62 D8-3.20 85-1.
49171 v 5-57.4R9-oo D
9-24.86RIO-oo DIO-1-50
86-1,49171v 6-57.4R11--20
,00Dll-0,15R12 20.00
Di2- 1.50 N 7-1.4917
1 ν 7-57.4R13-c.

Note that the eye point is set 16 mm behind the R13 apex.

fT -11,35, fR-18,0, fF -21,
61, fE -20,37 Numerical Example 2 Exit pupil diameter φ3 Maximum exit angle tanθ= 0.17
R1-oo D l= 1.80 N
1-1.77250 ν 1-49.6R2--1
2,4402-9,60 R3-7,85D 3-2.80 N 2-1.49
171υ2-57.4R4-148, 4104-28,
89 R5-17,8505-0,80N 3-1.8466
6shi 3-23.9R6-7, 27D 6-2.60
N 4-1.71300shi 4-53.887--18.
74 D 7-25.07R8-11,0-9D 8
-2.40 N 5-1.49171 5-57.4
R9-(X) 09 book 22.01 RIO wealth 1
44.93 010- 1.80 N 6
Maro 1.49171 ν 6-57.4R11 Snow -2
0,70Dll-0,15R12=20.70
Di2-1.80 87-1.49171 v 7-5
7.4R13--144,93 fT -11,34, fR ~ 15.39, fF -
22,56, fE -18,61 Numerical Example 3 Exit pupil diameter φ3 Maximum exit angle tanθ= 0.17
R1=5458.52 DI=2.60N
1=1.49171 Z/ l-57,4R2--8
,01D 2- 9.09R3-8,0103-2,
60N 2-1.49171 2-57.48 4-5
458.52 D 4-32.92R5-17,
7205-0,80N 3-1.84666shi3-23
．． 986- 7.24 06-2.60 N 4-1
．． 69680ν4-55.5R7--20,84D 7
-27.93R8-12,13D 8-2.40 N
5-1.49171 5-57.48 9=
oo D9=22.07RIO-389,
49010-1,80N 6■1.49171 White fog 5
7.4R11--19,15Dll-0,15R12-
19,15Di2- 1.80 N 7 1.
49171 ν 7-57.4R13-389,49 fT -11,30, fR-17,0, fF -24,
68, fE-18, 66 Table-1 (Effects of the Invention) As described above, according to the present invention, when employing the secondary imaging type as the finder optical system, each optical element is set as described above, and especially the relay By appropriately setting the refractive power of lenses, objective lenses, etc., we have achieved a secondary imaging type finder optical system with a simple configuration that allows observation of a finder image with a predetermined optical total length and high optical performance. can do.

[Brief explanation of the drawing]

1 to 3 are cross-sectional views of lenses of numerical embodiments 1 to 3 of the present invention, and FIGS. 4 to 6 are lens sectional views of numerical embodiment 1 of the present invention, respectively.
3 is a diagram showing various aberrations at an object distance of 3 m. In the figure, T is an objective lens, R is a relay lens, F is a field lens, E is an eyepiece lens, ΔM is a meridional image surface, and ΔS is a sagittal image surface. Patent applicant: Canon Co., Ltd. -1--" Figure 2 1) IL12L) 3 04 D5D6
F E 4th riU Day 1 Toka φ3 Pumi an&=0.17
tan9: 0.17th 5th
Zuli 8! Elongation ψ3i. 2op 2op -2pp Ki115JIK廠 Pu1 6Aθ Tsukasa, 17tMnθ=0.17 Sound

Claims (1)

[Claims] A finder image formed on the primary focus plane by an objective lens consisting of two positive lenses arranged with lens surfaces with strong curvature facing each other, is created by bonding a negative lens and a positive lens together. A finder image of an erect normal image is formed on the secondary focus plane through a relay lens consisting of a lens and a field lens consisting of a positive lens with a lens surface with a strong curvature facing the object side. When observing a finder image with an eyepiece consisting of two positive lenses arranged with lens surfaces with strong curvature facing each other, the objective lens,
The focal lengths of the relay lens, field lens, and eyepiece lens are fT, fR, fF, and fE in order, and the refractive index of the material of the negative lens and positive lens of the relay lens is N, respectively.
N, NP, the Abbe numbers of the materials of the negative and positive lenses of the relay lens are νN and νP, respectively, and the radius of curvature of the bonded lens surface of the cemented lens of the relay lens is RA, 1.0<fR/fT <1.8 1.0<fF/fE<1.7 0.3<|RA|/fR<0.6 0.07<NN-NP 25<νP-νN It is characterized by satisfying the following conditions. Secondary imaging finder optical system.