JPH02191908A - Kepler-type variable magnification finder - Google Patents

Abstract

PURPOSE:To reduce the change of dioptric power accompanied with varying of the magnification by constituting a finder of an objective lens consisting of first to third groups and an eyepiece lens consisting of a fourth group and moving the second group from the object side to the eyepiece side to increase the magnification. CONSTITUTION:This finder consists of the objective lens and the eyepiece lens. This objective lens consists of a first group 1 having a positive refracting power, a second group 2 having a negative refracting power, and a third group 3 having a positive refracting power and has a positive refracting power as the whole. The eyepiece lens consists of a fourth group 4 having a positive refracting power. An real image is formed between the third group 3 and the fourth group 4 by the objective lens and is observed through the eyepiece lens 4. The second group 2 is moved from the object side to the eyepiece side to increase the magnification.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a real image variable magnification finder. This finder can be used with 35mm lens shutter cameras, video cameras, electronic still cameras, etc.

[Prior Art] Conventionally, as a finder for a 351 lens shutter camera equipped with a zoom lens, a reverse Galilean finder that observes a virtual image formed by an objective lens through an eyepiece has been common.

However, this type of finder has a problem in that when trying to increase the variable power ratio, the lens diameter becomes extremely large.

On the other hand, Kevlar type finders, which form a real image with the objective lens and transmit it through the eyepiece, have the advantage that the lens diameter can be made smaller even if the zoom ratio is increased, although the overall length of the finder is longer. .

In recent years, as the zoom ratio of photographic lenses has increased, cameras have tended to become thicker, and Kepler-type viewfinders have come to be used as zoom finders.

[Problems to be Solved by the Invention] As a Kepler type finder that performs magnification change, the one disclosed in Japanese Patent Application Laid-Open No. 1983-7017 is known, but this finder has a magnification ratio of about 3 times. If it becomes larger, the difference between the diopter at the wide-angle end, the telephoto end, and the diopter at an intermediate position becomes large, so if the variable power ratio is increased, it becomes impractical as a finder.

In addition, as a Kepler type finder that corrects the above-mentioned diopter difference due to zooming, there is a
Those disclosed in Publication No. 18 and Publication No. 61-16073 are known. In these finders, the magnification is changed by the displacement of the second group, and the resulting change in diopter is corrected by the displacement of the first group, but the amount of movement of the first group to correct the diopter difference is This is not necessarily practical because it is large and difficult to design the lens moving mechanism.

The present invention has been made in view of the above-mentioned circumstances, and its first purpose is to perform zooming by moving only one group, to have a large zoom ratio of about 3 times, and to Firstly, it provides a real-image variable magnification finder with little change in diopter caused by changing the magnification (invention of claim 1).Secondly, the change in diopter caused by changing the magnification can be completely corrected and the diopter difference can be completely corrected. The object of the present invention is to provide a real image variable magnification finder which requires a small amount of group movement for correction, has a large variable magnification ratio of about 3 times, and has good optical performance (invention of claim 2).

[Means to solve the problem] One aspect of the present invention will be explained below.

The real image type variable magnification finder of the present invention has a four-group structure as claimed in claims 1 and 2, with the first to third groups forming an objective lens and the fourth group forming an eyepiece. The first to third groups that make up the objective lens have positive, negative, and positive refractive powers in that order, and have positive refractive power as a whole.Furthermore, the fourth group that makes up the eyepiece also has positive refractive power. The objective lens has a real image formed between the third group and the fourth group, and this real image is observed through the eyepiece.

The magnification is changed by moving the second group in the objective lens, and when the second group moves from the object side to the apex, the finder magnification increases.

In the second aspect of the present invention, the change in diopter of the finder due to the magnification change is corrected by moving the first group and the third group.

[Function] In Fig. 1, numeral 1 indicates the first group with positive refractive power, numeral 2 indicates the second group with negative refractive power, and numeral 3 indicates the third group with positive refractive power. It shows. These first to third groups 1 to 3
3 constitutes an objective lens, which has positive refractive power as a whole.

Reference numeral 4 indicates a fourth group constituting the eyepiece.

This fourth group 4 has positive refractive power.

A real image 6 formed between the third and fourth groups by the objective lens,
Observe 6m through the eyepiece.

In the first aspect of the invention, as described above, the magnification is changed by moving only the second lens group 2, and the other lens groups are fixed.

In the invention of claim 2 as well, the magnification is changed by moving the second group 2, but the first group 1
and the third group 3 are moved.

Here, for the following explanation, various symbols are defined as follows.

f,: focal length of the first group, f2: focal length of the second group, f
3: Focal length of the third group, f6. Focal length of the two objective lenses at the wide-angle end, f, Focal length at the intermediate position of the two objective lenses, r, t: Focal length of the objective lens at the telephoto end, f: Focus of the eyepiece Distance, β2. : Magnification of the second group at the wide-angle end, β2. : Magnification at the intermediate position of the second group, β2L: Magnification at the telephoto end of the second group, β3
: Magnification of the third group at the wide-angle end and telephoto end, β3. :3rd
Magnification at the intermediate position of the group, ΔTT2: Difference between the conjugate length at the wide-angle end and telephoto end of the second group and the conjugate length at the intermediate position, ΔX3: At the wide-angle end and telephoto end of the third group Object position W (
・Distance from the object point position (position indicated by reference numeral 5 in Fig. 1) to the intermediate position (distance indicated by reference numeral 5m in Fig. 1, Δ island: at the wide-angle end and telephoto end of the third group) Distance from the imaging position (position indicated by reference numeral 6 in FIG. 1) to the imaging position at an intermediate position! (position indicated by reference numeral 6m in FIG. 1), 2: Finder variable magnification ratio.

Note that the above β3. , ΔXiyΔxd, in the second aspect of the invention, are values before diopter change correction.

Further, regarding the invention of claim 2, ΔP8. : Amount of movement of the first group at the intermediate position during diopter correction, ΔP3.
: The amount of movement of the third group at the intermediate position during diopter correction (see Fig. 3).

Assuming that the conjugate lengths of the wide-angle end and the telephoto end of the second group 2 are equal,
The magnification of the second group is given as follows at the wide-angle end, intermediate position, and telephoto end.

β* −= −1/JT (
1) βx==-1 (2) βz t= -fr (3) Therefore, the difference between the conjugate length at the wide-angle end and telephoto end of the second group 2 and the conjugate length at the intermediate position is 6 lenses Tx.

ATT! =((1/□)+JT-2))・fs
(4) becomes.

In addition, the distance ΔX from the object point position 5 at the wide-angle end and telephoto end of No. 31 #3 to the object point position 5 m at the intermediate position is calculated using the following formula % % Imaging position of the third group 3 at the wide-angle end and telephoto end The distance ΔX from 6 to the intermediate imaging position of 116 m is given by the following equation.

Δ island = ΔX, β1m (6) From this, the finder diopter difference 1ΔDpl between the wide-angle end, the telephoto end, and the intermediate position is: 1Δop l = (I ΔX2 l /fH) X 10
00 (7).

In the finder disclosed in JP-A-62-7017, β
3-1, so the finder diopter difference 1ΔD'pl is.

1Δ0'P1: (1ΔXs l /fri X 10
00 (8) However, in the present invention, 1β3J can be set to a value smaller than 1, so 1Δx'a I < lΔ
xsl, and the diopter difference 1ΔDpl can be made smaller than 1ΔD'pI. That is, in the invention of claim 1, even though magnification is changed by displacing only the second group and fixing the other groups, the resulting finder diopter difference itself can be made sufficiently small.

In the invention of claim 2, the invention goes one step further and corrects the finder diopter difference 1ΔDpl by displacing the first group 1 and the third group 3.

As shown in FIG. 2, the first group 1 and the third group 3 are displaced at the intermediate position for diopter correction.

Referring to FIG. 3, the first group 1 and the second group 2 are ΔP1m
The third group 3 moves by ΔP1. Assuming that the imaging position 6m of the objective lens at the intermediate position is corrected by moving the object lens by a certain amount, the following equation holds true, assuming that the movement in the eyepiece direction is positive.

ΔX2=(A P,, -Δpt-)"β3.-ΔPs-
(9) Then, from both equations (6) and (9), ΔX, = (1-(1/ f' 1-))・A P1. −
Eight Pi, (10) is obtained.

From now on, in order to reduce the amount of movement of the correction group to keep the finder diopter constant, 1βU, +<1 (11)ΔP1
．． It is preferable to set it as =Δps-(12).

Using (10) and (12), ΔP1m”-β!, ΔX3=-ΔXs
(13).

That is, the first group 1. 2nd group 2. The third group 3 may be corrected by moving the third group 3 by an amount equal to the amount of deviation Δχ; in the direction opposite to the direction in which the deviation of the imaging position occurs.

At this time, from equation (11), 1ΔP1.1 is 1AX31
Therefore, the amount of movement of the first and third groups for diopter correction can be made smaller than in the conventional case.

In both the inventions of claims 1 and 2, (I) 2.0 < l f+/fz I
It is desirable to satisfy the condition <3.5.

This condition (I) concerns the distance between the first group 1 and the second group 2, and if the lower limit is exceeded, the distance becomes too narrow;
Actual lens placement becomes difficult.

If the upper limit is exceeded, the distance between the first and second groups becomes too large, and the lens diameter of the first group increases, making it impractical. Furthermore, it becomes difficult to correct aberrations.

Furthermore, in both the inventions of claims 1 and 2, (II) 0.3 <t/--r;;:
It is desirable to satisfy the following condition: :;=';;;=]/'f1G.

This condition (II) concerns the magnification of the third group; if the lower limit is exceeded, the absolute value of the magnification of the third group, 1β, 1, becomes too small, and the distance between the second and third groups at the wide-angle end decreases. becomes too large. This increases the lens diameter of the first group, making it impractical.

The distance between the second and third groups can be shortened by reducing f3, but if f3 is made too small, it becomes difficult to correct aberrations.

On the other hand, if the upper limit of condition (II) is exceeded, the magnification of the third group becomes large, and the effect of reducing the imaging position shift by the third group cannot be obtained.

Furthermore, both the inventions of claims 1 and 2 satisfy (III) 0.5 < l f□・f3/Cf1. i
It is desirable to satisfy the condition o*>+<2.

This condition (III) relates to the distance between the second group and the third group at the telephoto end, and if the lower limit is exceeded, the distance between the second group and the third group at the telephoto end.
The distance between the third groups becomes too small, making it difficult to actually construct the lens. Moreover, if the upper limit is exceeded, the lens diameter of the first group becomes large at the telephoto end, making it impractical.

Note that in the present invention, even if a condenser lens is not particularly provided in the vicinity of the imaging position, a light beam can be guided to the pupil by appropriately setting the focal lengths of the first to third groups.

[Example] Specific examples will be given below.

4 to 6 show specific lens configurations in each embodiment.

In Figures 4 to 6, the first
As in FIGS. 3 to 3, the first to fourth groups are shown. Further, reference numeral 7 indicates a Porro prism for inverting the real image formed by the objective lens horizontally and vertically, developed as a glass block for the sake of simplicity.

In each example, the radius of curvature of the first surface from the object side (including the entrance/exit surface of the Porro prism 7) is r, the distance between the surfaces is 6, and the j-th optical element from the object side (Porro prism 7 The refractive index and Atsube number of the material (including 7) are nj and ν, respectively.
, and so on.

The lens surface with the main lens is an aspherical surface, and as is well known, the amount of change in the direction of the optical axis is X, the amount of displacement in the direction perpendicular to the optical axis is y1, the conic constant is A4-As, and the aspherical coefficient is A4-As. , x=(1/ri)・y”/[1+ −+ to −y/rs
)”]÷A4・'/4+1.・y6.

Among the six examples listed below, Examples 1 to 3 are examples related to the invention of claim 1.

Example 1 The first group 1 has a two-lens configuration, the second group 2 has a two-lens configuration, the third group 3 has a three-lens configuration, and the fourth group 4 has a single lens configuration.

Half angle of view 31.7 to 11.6 degrees i ri ctl j
nj v sl -373,355111,
491957,42" 10,418 1.5 3 ning 9.276 4 ning -13,943 5-84,688 6 ning 5.417 7 car -4,951 8-7,141 973,892 10-22,934 1131,886 12-46,922 1319,556 14” -27,181 1s o.

17 pieces 33.906 18” -17,495 Variable distance angle of view (degrees) d Hatake variable 2.6 Variable 0.2 0.2 24.143 0.2 3.5 1.4919 57.4 1.4919 57 .4 1.4919 57.4 1.4919 57.4 1.4919 57.4 1.4919 57.4 1.5168 64.2 1.4919 57.4 11.6 31.7 0.488 16.8 8.324 9.989 4.133 9.705 0.751 Aspheric i Example 2 First group 1 consists of two elements, second group 2 consists of two elements, third group 3 consists of three elements, 4th g4 is composed of two sheets.

Half angle of view 31.7 to 11.6 degrees r amount d.

38.017 1 9.133 1.5 11.23 3 -14.204 Variable -41,0351 ν　j J 57.4 57.4 57.4 1.4919 1.4919 1.4919 to -1,986 -0,12 -10,892 -1,538 -0,55 -42,198 -10,056 -3,303 8,041 -8,695 -26,375 52,353 -27,838 29,881 -39,543 21,944 -41,046 38,741 -104,732 18,819 49,456 variable distance Angle of view (degrees) 31.7 d, 0.415 d, 10.318 Aspherical surface 2.7 variable 0.2 27.77 0.2 3.5 0.2 1.5 1.4919 1.4919 1.4919 1.4919 1.5168 1.4919 1.4919 18.8 11.6 6.638 10.23 4.092 0.503 57.4 57.4 57.4 57.4 64.2 57.4 57.4 i k 2 -0.868 3 -0.0411 4 -9.893 8 -1.941 7 -1.135 9 -19.806 13 -3.373 14 -44.249 Example 3 The first group 1 has a single lens configuration.

The third group 3 is composed of three elements, It is.

Half angle of view 31.7 to 11.6 degrees i r five di
jl 38.464 5 1 2" -38,555 variable 3 27.589 1 2 4" 10.897 2.7 51 -13.532 1 3 The second group 2 consists of two elements.

The fourth group 4 has two elements j ν j 1.4919 57.4 1.4919 57.4 1.4919 57.4 Variable 0.2 0.2 21.497 0.2 3.5 0.2 1. 5 48.727 84.477 -31.676 32.734 -36.582 29.365 -39.029 -166.45 -17.612 17.233 33.868 Variable distance angle of view (degrees) 31.7 d , 0.186 d, 19.311 Aspherical surface 2 -13.459 1.4919 57.4 1.4919 57.4 1.4919 57.4 1.5188 64.2 1.4919 57.4 1.4919 57.4 16.9 11.8 9.883 15.17? 9.794 4.3 4 -1.767 0
05 -2.662 0
07 -15.814
0 08 -2.155
0 012-50.818
0 015 -158.155
0 0IS -3,
74700 Examples 4 to 6 listed below are examples related to the invention of claim 2.

Example 4 The lens configuration is the same as in Example 1 above. The surface spacing d8 in the first embodiment is variable.

Variable distance angle of view (degrees) 31.7 19.8 11.6d4
0,468 5.156 9.705d,
9.989 5.301 0.751d, 423.
587 24.625 23.567 Example 5 The lens configuration is the same as in Example 2 above. The surface spacing d14 in the second embodiment is variable.

Variable distance angle of view (degrees) 31.7 19.6 11.6d,
0.415 5.396 10.23d,
10.31B 5.336 0.503d,
426,952. 28.427 26.952 Example 6 The lens configuration is the same as in Example 3 above. The surface spacing d1 in the above Example 3! is variable.

Variable distance angle of view (degrees) 31.7 19.6 11.6dz
O, 1867, 94215, 177d,
19.311 11.535 4.3d+x 2
0.929 21.74 20.929 Also, the condition (
The values of each parameter of I), (II), and (III) are shown in the following table.

Table parameters Example number (1, 4) (2, 5) I fdfx I 2.75 2.824
f possible w”fo ふ 〇, 843 0.722 (3
,6) 3.077 0.435 1ft・f3baf2・f,,)+1.318 1
．． 318 1.438 Figures 7 to 9 show Example 1
Aberration diagrams related to Examples 4 to 3 are sequentially shown, and aberration diagrams related to Examples 4 to 6 are sequentially shown in FIGS. 10 to 12.

In each map, S represents the sagittal image surface, 1M represents the meridional image surface, H represents the pupil height, and ω represents the half angle of view.

[Effects of the Invention] According to the present invention, a novel real-image variable magnification finder can be provided.

This finder has the structure shown above, so
Although the finder of the first aspect has a high zoom ratio, the change in diopter due to zooming is small.

In the finder according to the second aspect of the present invention, the above-mentioned diopter change can be substantially eliminated. Furthermore, it has high performance and is suitable for practical use.

[Brief explanation of the drawing]

FIG. 1 is a diagram for explaining magnification change of the finder of the present invention, FIGS. 2 and 3 are diagrams for explaining diopter correction according to the invention of claim 2, and FIGS. 4 to 6 is a diagram showing the lens configuration of the example, and FIGS. 7 to 1z are aberration diagrams related to the example. 100. Group 1, 290. Group 2, 316. Group 3, 4
00. Group 4, 500. Object point position, 609. Imaging form γ by objective lens /'1JrJ (ntF(m) !S aberration & c%) Spherical aberration h aberration (!toPteυ (draf'tar) distortion a disturbance (%) Bath 6 ■ Intermediate view angle wide angle 1ft) 40 Intermediate view dojo W -2C H1 arrival. U = / Ita' w = / (C" Distortion aberration (power taste @ J adjustment (tl; op) Yuzenfukkei (d layer fty) Zekubuko (power wide-angle end (Iiν 'hp) (17I7/7m6F) Mukakupo-tei 7/

Claims (1)

[Claims] 1. Consists of an objective lens and an eyepiece lens, the objective lens having a first group having a positive refractive power, a second group having a negative refractive power, and a third group having a positive refractive power. The eyepiece lens is a fourth group having positive refractive power, and the objective lens forms a real image between the third and fourth groups, and this real image is A real image type variable magnification finder configured to be observed through an eyepiece, and characterized in that the magnification is increased by moving the second group from the object side to the eyepiece side. 2. The real image variable magnification according to claim 1, characterized in that a change in finder diopter due to magnification caused by movement of the second group is corrected by displacement of the first group and the third group. Finder.