JP5725971B2 - Viewfinder optical system and imaging apparatus using the same - Google Patents

Description

  The present invention relates to a finder optical system and an image pickup apparatus using the same, and is particularly suitable for an image pickup apparatus such as a digital single-lens reflex camera or a video camera that can observe a finder image favorably with a large observation magnification of the finder optical system. It is a thing.

  Conventionally, in a single-lens reflex camera, a subject image (finder image) formed on a focusing screen is observed through a finder optical system by a photographing lens (objective lens). In this finder optical system, an object image formed on a focusing screen is converted into an erect image through an image inverting member such as a pentaprism or a penta roof mirror, and then magnified and observed by an eyepiece optical system (eyepiece lens). It is configured.

  An eyepiece used in such a viewfinder optical system is required to have a high observation magnification, a sufficiently long eye relief, and diopter adjustment. Here, the eye relief is the distance from the eye point side lens surface of the eyepiece optical system to the eye point.

  In general, in such a finder optical system, the observation magnification is obtained by the ratio of the focal length of the taking lens and the eyepiece optical system. For this reason, in order to increase the observation magnification, it is necessary to shorten the focal length of the eyepiece optical system. However, in a finder optical system of a single-lens reflex camera, it is generally necessary to set the diopter (finder diopter) to around −1 diopter (dpt) [1 / m]. Therefore, the focal length of the eyepiece optical system is substantially determined by the distance from the focusing screen on which the object image is formed to the eyepiece optical system (the optical path length to the main point position of the eyepiece optical system).

  Therefore, in order to increase the observation magnification of the finder optical system in a single-lens reflex camera, it is preferable to shorten the optical path length of the image inverting member and shorten the distance from the focusing screen to the principal point of the eyepiece optical system. That is, the eyepiece optical system is preferably arranged as close as possible to the focusing screen side. However, if this method is used to increase the observation magnification, the viewfinder optical system is recessed closer to the object side than the back of the camera (imaging device). As a result, the distance from the apex of the lens surface closest to the eye point of the eyepiece lens to the rear end surface of the camera body becomes longer, making it difficult for the observer to bring the eye closer to the viewfinder optical system.

  If the eye relief is made sufficiently long, the image reversing member must be enlarged in order to reduce vignetting on the exit surface of the image reversing member. As a result, the optical path length of the image inverting member is inevitably increased, and the observation magnification of the finder optical system is lowered. Thus, in the finder optical system of a single-lens reflex camera, increasing the observation magnification and increasing the eye relief are contradictory.

  Conventionally, in order to increase the observation magnification and lengthen the eye relief, the eyepiece optical system (eyepiece lens) in order from the object side has a negative refractive power lens group, a positive refractive power lens group, a positive or negative refractive power. A finder optical system having a three-group configuration of force lens groups is known. Of these, a finder optical system in which the shape factors of the first lens group and the third lens group are appropriately set is known (Patent Document 1). In addition, a finder optical system having such a three-group configuration in which the first lens group includes a negative meniscus lens and the third lens group includes two lenses is known (Patent Document 2).

Japanese Patent Laid-Open No. 9-329752 JP 2009-20220 A

  In recent years, with the digitization of cameras (imaging devices), a liquid crystal screen and various electronic components are arranged on the back of the camera, and the distance from the image sensor surface to the rear end surface of the camera has become significantly longer. In order to make it easier for the photographer to look into the eyepiece optical system, it is necessary to sufficiently increase the distance from the eye point to the rear end surface of the camera. If the distance from the most object-side lens surface of the eyepiece optical system, which is the entire length of the eyepiece optical system, to the eyepoint side surface is insufficient, it is difficult to observe the viewfinder image.

  In other words, when the eye point side surface of the eyepiece optical system is arranged at a position deeper than the back of the camera, the observer must bring the face into close contact with the camera in order to see the entire screen. Convenience is not good.

  On the other hand, when the eyepiece optical system is arranged near the rear end surface of the camera, the distance from the focusing screen to the eyepiece optical system becomes long, and it is difficult to increase the observation magnification. Further, if the eye relief of the eyepiece optical system arranged near the rear end of the camera is made sufficiently long, the image reversing member must be enlarged as described above, and the optical path length of the image reversing member is long. Become. That is, the distance from the focusing screen to the eyepiece optical system becomes longer, and it becomes more difficult to increase the observation magnification.

  Thus, in the finder optical system of a single-lens reflex camera, having functions such as a high observation magnification and a long eye relief leads to an improvement in convenience for the observer. However, with the digitalization of the imaging device, it is more difficult to achieve each of these functions with a single finder optical system because the entire optical system is complicated and each function is performed well.

  It is an object of the present invention to provide a finder optical system having a high observation magnification and an image pickup apparatus having the same while maintaining a sufficient distance from the focusing screen to the eyepiece optical system.

The finder optical system of the present invention is a finder optical system for observing an object image formed on a predetermined surface by a photographic lens.The finder optical system is a condenser lens having a positive refractive power in order from the object side to the observation side. An image reversing member for making an object image an erect image, a first lens group having a negative refractive power, a second lens group having a positive refractive power, and a third lens group having a positive or negative refractive power, and a diopter A finder optical system in which the distance between adjacent lens groups changes during adjustment,
The air-converted optical path length on the optical axis from the rear principal point position of the condenser lens to the front principal point position of the first lens group is H1, and the light from the predetermined surface to the observation side surface of the third lens group When the air equivalent optical path length on the axis is d,
0.50 <H1 / d <0.73
It satisfies the following conditional expression.

  According to the present invention, a finder optical system having a high observation magnification can be obtained while maintaining a sufficient distance from the focusing screen to the eyepiece optical system.

It is a schematic block diagram of the single-lens reflex camera provided with the finder optical system which concerns on Example 1 of this invention. It is an expanded view along the optical axis of the finder optical system which concerns on Example 1 of this invention. It is each aberration of the finder optical system which concerns on Example 1 of this invention. It is an expanded view along the optical axis of the finder optical system which concerns on Example 2 of this invention. It is each aberration of the finder optical system which concerns on Example 2 of this invention. It is an expanded view along the optical axis of the finder optical system which concerns on Example 3 of this invention. It is each aberration of the finder optical system which concerns on Example 3 of this invention.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The finder optical system of the present invention observes an object image (finder image) formed on a predetermined surface, for example, a focusing screen, by an imaging lens (objective lens) through an eyepiece. The finder optical system includes, in order from the predetermined surface side to the observation side, a condenser lens having a positive refractive power, an image inverting member for erecting an image such as a pentaprism, a first lens group having a negative refractive power, and a positive refractive power. The second lens group includes a third lens group having a positive or negative refractive power.

  The imaging apparatus of the present invention includes a finder optical system, a photographing lens that forms an image corresponding to a subject image displayed by the finder optical system, and an imaging unit that receives the image.

  FIG. 1 is a cross-sectional view of a main part when the finder optical system according to the first embodiment of the present invention is applied to a single-lens reflex camera (imaging device). 2 and 3 are an optical path diagram and an aberration diagram in which the optical paths of a part of the optical elements of the finder optical system according to the first embodiment of the present invention are developed. 4 and 5 are an optical path diagram and an aberration diagram in which the optical paths of a part of optical elements in the finder optical system according to the second embodiment of the present invention are developed. 6 and 7 are an optical path diagram and an aberration diagram in which the optical paths of a part of the optical elements in the finder optical system according to the third embodiment of the present invention are developed.

  In the optical path diagram and the aberration diagram, the viewfinder diopter is -1 diopter (standard diopter). In the optical path diagram, the left side where the inverting optical system 5 for forming an erect image is located is the object side (light incident side), and the right side of the eye point 7 side is the observation side (light emitting side). Further, in the optical path diagram, the optical path from the mat surface 3a of the focusing screen 3 described later to the eye point 7 is shown with each reflecting surface of the penta roof mirror 5 omitted.

  In FIG. 1, reference numeral 1 denotes a photographing lens fixed to a camera body (not shown) or detachably mounted. Reference numeral 2 denotes a quick return mirror which can be rotated around a rotation shaft 2a. Reference numeral 3 denotes a focusing screen, on which a finder image (subject image) (object image) is formed on the mat surface 3a.

  4 is a condenser lens, and 5 is a pentaprism (image reversal member) as an erect image forming member. The finder image on the mat surface 3a of the focusing screen 3 is an erect image. Reference numeral 6 denotes an eyepiece optical system. Reference numeral 7 denotes the position of the eye point (observation position) (the position of the pupil of the observer). IP is an image plane of the photographing lens 1 and corresponds to an imaging surface of a solid-state imaging device (imaging means) of a CCD sensor or a CMOS sensor or a photosensitive surface of a film (imaging means).

  In the finder optical system in this embodiment, the subject image formed by the photographing lens 1 is reflected by the quick return mirror 2 and formed on the mat surface 3 a (predetermined surface) on the focusing screen 3. The finder image formed on the mat surface 3a is observed from the eye point 7 through the eyepiece optical system 6 through the eyepiece optical system 6 as an erect image through the condenser lens 4 and the pentaprism 5.

  In each embodiment, the eyepiece optical system 6 includes three lens groups including a first lens unit L1 having a negative refractive power, a second lens unit L2 having a positive refractive power, and a third lens unit L3 having a positive or negative refractive power. Is made up of.

  The first lens unit L1 includes one negative lens 6a having concave concave surfaces. The second lens unit L2 includes a positive lens 6b having convex lens surfaces. The third lens unit L3 includes a positive lens 6c having a convex surface on the object side and a negative lens 6d having a concave surface on the observation side.

The viewfinder diopter is adjusted by moving the second lens unit L2 on the optical axis. In other words, in each embodiment, the distance between adjacent lens groups changes during diopter adjustment. As an image inverting member applicable in the present embodiment, any optical member capable of inverting an image upright, such as a Porro prism and a roof prism, in addition to a penta roof prism, may be used. The condenser lens 4 is a positive meniscus lens having a convex surface on the observation side.

  In the aberration diagram, the pupil diameter is a spherical aberration and the height at the eye point 7 is shown. d indicates a d line, and F indicates an F line. The image height indicates the height of the finder image on the mat surface 3a. In astigmatism, ΔM is a meridional image plane, and ΔS is a sagittal image plane. Chromatic aberration is lateral chromatic aberration. The maximum image height is the same in all astigmatism diagrams, distortion diagrams, and chromatic aberration diagrams.

In each embodiment, the principal point interval between the condenser lens 4 and the first lens unit L1 is H1. Let d be the air-converted optical path length along the optical axis from the predetermined surface 3a to the observation side surface of the third lens group. At this time,
0.50 <H1 / d <0.73 (1)
The following conditional expression is satisfied.

  Conditional expression (1) follows the principal point interval H1 from the condenser lens 4 to the negative lens 6a and the optical axis from a predetermined surface (mat surface 3a) on the focusing screen 3 to the last lens surface of the eyepiece optical system 6. It is a formula regarding the ratio of the air-converted optical path length d.

  Conditional expression (1) secures a sufficient optical total length as a finder optical system for a single-lens reflex camera while having a relatively simple lens configuration. Further, the observation magnification of the finder optical system is set sufficiently large so that the principal point position of the eyepiece optical system is positioned on the object side (penta prism side). Furthermore, it is a condition for arranging the exit pupil position of the eyepiece optical system and the position of the observer's pupil sufficiently behind the eyepiece optical system 6 so that a good finder image can be observed. If the conditional expression (1) is deviated, it becomes difficult to obtain the above-described effect.

  The finder optical system according to each embodiment satisfies the above-described conditions so that the finder observation magnification is sufficiently increased and the finder diopter adjustment is facilitated while ensuring a sufficiently long eye relief. A good viewfinder image is observed.

In each embodiment, it is more preferable to satisfy one or more of the following conditions. The focal lengths of the condenser lens 4, the first lens unit L1, and the second lens unit L2 are fc, f1, and f2, respectively. Let f be the focal length of the finder optical system when the finder diopter is -1 dpt (diopter). The image inverting member 5 is a prism, and the refractive index of the material of the prism is nd. The radius of curvature of the lens surface located closest to the object side in the first lens group is R1s, the radius of curvature of the lens surface located closest to the observation side in the first lens group is R1e, and is the largest among the second lens group. The radius of curvature of the lens surface located on the object side is R2s, and the radius of curvature of the lens surface located closest to the observation side in the second lens group is R2e. At this time, it is preferable to satisfy one or more of the following conditional expressions.

0.80 <| fc × f1 | / H12 <2.0 (2)
0.48 <f2 / f <0.65 (3)
1.6 <nd (4)
−0.71 <(R1s + R1e) / (R1s−R1e) <0.71 (5)
−0.71 <(R2s + R2e) / (R2s−R2e) <0.71 (6)

  Next, the technical meaning of each conditional expression described above will be described. Conditional expression (2) is an expression related to the power distribution of the condenser lens and the first lens unit L1 (the combined power when there are a plurality of lenses in the first lens unit L1). Conditional expression (3) is an expression relating to power distribution of the second lens unit L2. Although these conditional expressions (2) and (3) have a relatively simple lens configuration as in conditional expression (1), they ensure a sufficient optical total length as a finder optical system for a single-lens reflex camera.

  Furthermore, the observation point of the finder optical system is set sufficiently large so that the principal point position of the eyepiece optical system is positioned on the object side (penta prism side). Furthermore, it is a condition for arranging the exit pupil position of the eyepiece optical system and the position of the observer's pupil sufficiently behind the eyepiece optical system 6 so that a good finder image can be observed. If these conditional expressions (2) and (3) are deviated, it becomes difficult to obtain the above-described effects.

  Conditional expression (4) is an expression relating to the refractive index of the material when the image inverting member is formed of a pentaprism. Conditional expression (5) relates to the shape factor of the negative lens 6a when the first lens unit L1 is composed of one negative lens 6a. Conditional expression (6) is related to the second lens unit L2 as one positive lens. This is an expression relating to the shape factor of the positive lens 6b when configured by 6b.

  These conditional expressions (4), (5), and (6) have the same effects as the conditional expressions (1), (2), and (3) described above. That is, a sufficient optical total length is secured as a finder optical system for a single-lens reflex camera while having a relatively simple lens configuration. Further, the observation magnification of the finder optical system is set sufficiently large so that the principal point position of the eyepiece optical system is positioned on the object side (penta prism side). Furthermore, it is a condition for simultaneously locating the exit pupil position of the eyepiece lens system and the position of the observer's pupil sufficiently behind the eyepiece so that a good finder image can be observed.

  In each embodiment, the third lens unit L3 includes at least one positive lens and at least one negative lens. Thereby, the finder image is observed favorably. As described above, according to each embodiment, a finder optical system suitable for a single-lens reflex camera with high observation magnification, long eye relief, and high optical performance can be obtained.

  Below, the specification of the numerical Example of each Example of FIG.2, FIG.4, FIG.6 is shown. In numerical examples, r i is the radius of curvature of the i-th lens surface in order from the mat surface 3a side of the focusing screen to the observation side, and d i is the i-th lens thickness and air spacing. Ni and νi are the refractive index and Abbe number of the material of the i-th lens, respectively. r1 corresponds to the mat surface 3a. r 2 and r 3 correspond to the condenser lens 4.

r4 and r5 correspond to the entrance surface and the exit surface of the penta roof prism 5, respectively. r6 to r13 correspond to the eyepiece 6. r14 corresponds to an eye point. In each numerical example, * represents an aspherical surface. The aspherical shape has an X axis in the optical axis direction, a Y axis in the direction perpendicular to the optical axis, a positive light traveling direction, R is a paraxial radius of curvature, and K is a conic constant. Also, c2, c4, c6, c8, and c10 are aspherical coefficients. At this time,

Is defined by The display of “e-0X” means “10 ^−X ”. The viewfinder diopter and the interval change when the diopter is adjusted by the second lens unit L2 are shown. The relationship between the viewfinder diopter and the focal length of the eyepiece 6 is shown. Table 1 shows the relationship between the above-described conditional expressions and numerical examples.

[Numerical Example 1]
Paraxial radius of curvature Axis top spacing Refractive index (Nd) Abbe number (νd)
r1 = ∞ d1 = 4.28
r2 = -131.94 d2 = 4.25 N1 = 1.71 ν1 = 53.87
r3 = -57.15 d3 = 0.67
r4 = ∞ d4 = 93.21 N2 = 1.77 ν2 = 49.60
r5 = ∞ d5 = 2.60
r6 = -40.00 d6 = 3.00 N3 = 1.85 ν3 = 23.78
r7 = 151.56 d7 = variable
r8 = 59.85 d8 = 6.30 N4 = 1.77 ν4 = 49.60
r9 = -59.85 d9 = variable
r10 = 31.53 d10 = 6.68 N5 = 1.84 ν5 = 42.71
r11 = -78.46 d11 = 0.60
r12 * = 7326.14 d12 = 5.50 N6 = 1.85 ν6 = 40.10
r13 * = 25.08 d13 = 20.00
r14 = ∞

Aspheric coefficient
r12 r13
k -8.17E + 05 5.98E-01
c2 0.00 0.00
c4 -8.81E-06 4.13E-06
c6 -1.09E-07 -2.97E-07
c8 3.04E-10 2.40E-10
c10 0.00 4.04E-12

Variable interval diopter [Diopter-] -1.00 -3.00 +1.00
d7 2.40 0.91 3.79
d9 2.92 4.41 1.53

Focal length diopter [Diopter-] -1.00 -3.00 +1.00
Focal length 66.18 69.08 63.64

[Numerical Example 2]
Paraxial radius of curvature Axis top spacing Refractive index (Nd) Abbe number (νd)
r1 = ∞ d1 = 2.80
r2 = -150.00 d2 = 4.80 N1 = 1.80 ν1 = 46.57
r3 = -48.00 d3 = 0.67
r4 = ∞ d4 = 96.00 N2 = 1.81 ν2 = 40.92
r5 = ∞ d5 = 1.80
r6 = -87.17 d6 = 1.51 N3 = 1.85 ν3 = 23.78
r7 = 57.31 d7 = variable
r8 = 45.16 d8 = 6.43 N4 = 1.77 ν4 = 49.60
r9 = -45.16 d9 = variable
r10 = 35.52 d10 = 5.00 N5 = 1.83 ν5 = 42.71
r11 = -1066.74 d11 = 0.65
r12 * = -251.12 d12 = 6.60 N6 = 1.85 ν6 = 40.39
r13 * = 33.52 d13 = 20.00
r14 = ∞

Aspheric coefficient
r12 r13
k 195.09 5.55
c2 0.00 0.00
c4 -7.79E-06 -2.10E-05
c6 -2.05E-08 -3.39E-07
c8 7.65E-11 3.60E-09
c10 0.00 -2.22E-11

Variable interval diopter [Diopter-] -1.00 -3.00 +1.00
d7 3.06 1.60 4.50
d9 2.96 4.42 1.52

Focal length diopter [Diopter-] -1.00 -3.00 +1.00
Focal length 59.56 58.99 60.14

[Numerical Example 3]
Paraxial radius of curvature Axis top spacing Refractive index (Nd) Abbe number (νd)
r1 = ∞ d1 = 4.30
r2 = -131.94 d2 = 4.25 N1 = 1.80 ν1 = 46.57
r3 = -57.15 d3 = 0.67
r4 = ∞ d4 = 93.21 N2 = 1.66 ν2 = 50.88
r5 = ∞ d5 = 2.80
r6 = -42.28 d6 = 3.26 N3 = 1.85 ν3 = 23.78
r7 = 235.08 d7 = variable
r8 = 150.41 d8 = 6.20 N4 = 1.83 ν4 = 42.71
r9 = -40.71 d9 = variable
r10 = 21.12 d10 = 6.30 N5 = 1.77 ν5 = 49.60
r11 = ∞ d11 = 0.60
r12 = -907.84 d12 = 4.50 N6 = 1.85 ν6 = 40.10
r13 * = 20.95 d13 = 20.00
r14 = ∞

Aspheric coefficient
r13
k -1.63
c2 0.00
c4 3.15E-05
c6 7.31E-08
c8 4.50E-10
c10 -4.57E-12

Variable interval diopter [Diopter-] -1.00 -3.00 +1.00
d7 3.05 1.50 4.54
d9 3.29 4.84 1.80

Focal length diopter [Diopter-] -1.00 -3.00 +1.00
Focal length 65.87 67.28 64.56

DESCRIPTION OF SYMBOLS 1 Shooting lens 2 Quick return mirror 3 Focus plate 4 Condenser lens 5 Image inversion member 6 Eyepiece optical system L1 1st lens group L2 2nd lens group L3 3rd lens group 7 Eye point

Claims (6)

In a finder optical system for observing an object image formed on a predetermined surface by a photographic lens, the finder optical system is a condenser lens having a positive refractive power in order from the object side to the observation side, and makes the object image an erect image. image reversing member, the first lens unit having a negative refractive power, a second lens unit having a positive refractive power and a third lens unit of positive or negative refractive power, the distance between lens adjacent when diopter Is a finder optical system that changes
The air-converted optical path length on the optical axis from the rear principal point position of the condenser lens to the front principal point position of the first lens group is H1, and the light from the predetermined surface to the observation side surface of the third lens group When the air equivalent optical path length on the axis is d,
0.50 <H1 / d <0.73
A finder optical system characterized by satisfying the following conditional expression: When the focal lengths of the condenser lens, the first lens group, and the second lens group are fc, f1, and f2, respectively, and the focal length of the finder optical system when the finder diopter is −1 diopter, f.
0.80 <| fc × f1 | / H1 ² <2.0
0.48 <f2 / f <0.65
The finder optical system according to claim 1, wherein the following conditional expression is satisfied. The image inverting member is a prism, and when the refractive index of the material of the prism is nd,
1.6 <nd
The finder optical system according to claim 1 or 2, wherein the following conditional expression is satisfied. The radius of curvature of the lens surface located closest to the object side in the first lens group is R1s, the radius of curvature of the lens surface located closest to the observation side in the first lens group is R1e, and the radius of curvature of the second lens group. When the radius of curvature of the lens surface located closest to the object is R2s and the radius of curvature of the lens surface located closest to the observation side in the second lens group is R2e,
−0.71 <(R1s + R1e) / (R1s−R1e) <0.71
−0.71 <(R2s + R2e) / (R2s−R2e) <0.71
The finder optical system according to any one of claims 1 to 3, wherein the following conditional expression is satisfied.   The viewfinder optical system according to any one of claims 1 to 4, wherein the third lens group includes at least one positive lens and at least one negative lens.   6. An imaging apparatus comprising: the finder optical system according to claim 1; and an imaging unit that receives an image corresponding to an object image displayed by the finder optical system.