JPH07218985A - Optical system of finder - Google Patents

Abstract

PURPOSE:To satisfactorily observe a finder image while miniaturizing the finder optical system by observing an object image through an optical member provided with refracting power, planar beam splitting element and eyepiece successively from the side of an object. CONSTITUTION:An optical member 2 is arranged near a light exit surface 52b of a pentaprism 52, namely, at a position faced to an eyepiece 1 with a dychroic mirror 67 between. Then, the finder image formed on a focusing plate 51 is passed through the pentaprism 52 by a photographic lens and observed later through the optical member 2 arranged near the light exit surface 52b of the pentaprism 52, dychroic mirror 67 and eyepiece 1. Thus, eyeball information is provided by forming the reflected image of an eyeball 501 of an observer on the light receiving surface of a detecting element 57. The position of an image (first Purkinje image) due to the center of the image of the pupil and the cornea is calculated by using the eyeball information provided from the detecting element 57, and the direction of line of sight of the observer is detected from the relative position relation between both of them.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a finder optical system, and in particular, a finder which is relatively small and has a good size by appropriately configuring each element despite having a plate-like light splitting element in the optical path. A photographing device such as a still camera or a video camera, which enables observation of an image,
Alternatively, the present invention relates to a finder optical system suitable for an observation device such as a measuring instrument and an inspecting instrument.

[0002]

2. Description of the Related Art Heretofore, various finder optical systems have been proposed as finder optical systems in which a light splitting element is provided in the vicinity of an eyepiece and a light beam split by the light splitting element performs an additional function. ing.

One of the functions is to detect the line of sight of the observer. This is the line of sight of the observer observing the finder image, that is, the finder field of view and its peripheral portion, by detecting the position where the observer is gazing,
This makes it possible to input information necessary for using various additional devices without using other special operating members.

When the finder optical system having such a function of detecting the line of sight is applied to, for example, an automatic focus detection camera which selects a distance measuring point from a plurality of areas within a photographing area, the focus within the finder field of view is obtained. There is a feature that the distance measuring point can be selected by gazing at the area to be adjusted.

FIG. 14 is a schematic view of a main part near a viewfinder optical system of a conventional single-lens reflex camera having a function of detecting the line of sight of an observer.

In the figure, 51 is a focusing screen, on the surface of which a finder image is formed by a taking lens (not shown). Reference numeral 52 is an erecting prism, which is a so-called penta prism.

Reference numeral 53 denotes an eyepiece lens, which guides a light beam La from an object to an observer's eye 501 to observe a finder image on the focusing screen 51. 59 is the cornea of the observer's eye 501, 60 is the iris, and 61 is the pupil.

Reference numeral 54 denotes a light splitting element (dichroic prism), which has a light splitting surface 55 that transmits visible light and reflects infrared light.

Reference numeral 58 denotes a light emitting diode which emits infrared light, 5
Reference numeral 7 is a detection element formed of an area sensor or the like, and reference numeral 56 is an imaging lens for guiding the infrared light from the light emitting diode 58 to the detection element 57.

In such a structure, the observer observes the finder image formed on the focusing screen 51 by the taking lens (not shown) through the penta prism 52, the dichroic prism 54, and the eyepiece lens 53.

The pentaprism 52 allows an observer to observe the finder image as an erect image, and reflects and deflects the finder image formed on the focusing screen 51 so as to downsize the entire finder optical system. There is.

On the other hand, the light emitted from the light emitting diode 58,
The infrared light reflected by the eyeball 501 passes through the eyepiece lens 53 in the opposite direction to the light beam La, and is reflected upward by the light splitting surface 55 of the dichroic prism 54. Then, the light is guided onto the light receiving element 57 by the imaging lens 56, and the eyeball 5
The reflected image of No. 01 is formed.

FIG. 15 schematically shows a reflection image formed on the light receiving element 57. In FIG. 15, 62,
Reference numerals 63 show images of the iris and the pupil, respectively. 64 is shown in FIG.
The reflected image (first Purkinje image) by the cornea 59 shown in FIG. A method of detecting the line-of-sight direction of an observer from the image thus obtained is disclosed in, for example, Japanese Patent Laid-Open No. 61-17255.
No. 2 publication. This is to process the image signal obtained by the light receiving element 57 to obtain the positions of the center of the pupil image 63 and the first Purkinje image 64, and detect the line-of-sight direction of the observer from the relative positional relationship between the two. is there.

In addition to the structure shown in FIG. 14, as shown in FIG. 16, a light emitting diode 58, a light projecting lens 65, and a half mirror 66 are arranged between the light splitting element 54 and the light receiving element 57, and a luminous flux for illumination is arranged. It is also known to irradiate the eyeball 501 as a parallel light flux along the finder optical axis.

Incidentally, as shown in FIG. 17, it is possible to replace the dichroic prism 54 of FIG. 14 with a dichroic mirror 67. Dichroic mirror 67
The surface 68 of is the light splitting surface 5 of the dichroic prism 54.
Like No. 5, it has a characteristic of transmitting visible light and reflecting infrared light.

[0016]

The process for manufacturing the dichroic prism 54 used in the line-of-sight detection system as shown in FIG. 14 includes the steps of glass material grinding, polishing, dichroic film deposition, and transparent film formation on the entrance / exit surface. There are a wide variety of methods such as vapor deposition, laminating, and blackening, which inevitably become expensive.

As a method for avoiding this, there is a method in which the material of the dichroic prism is plastic.

However, plastic is inferior in weather resistance to glass. In addition, there is a problem that in order to accurately manufacture a large block such as a dichroic prism with plastic, it is necessary to manufacture the block with sufficient molding time by using appropriate equipment. Therefore, it does not necessarily lead to a significant cost reduction.

On the other hand, the dichroic mirror 67 used in FIG. 17 has a simple manufacturing process and is suitable for mass production of one having uniform characteristics. Therefore, it is important to replace the dichroic prism in FIG. 14 with a dichroic mirror in order to simplify the manufacturing process, and it is possible to significantly reduce the cost.

However, when the dichroic prism 54 shown in FIG. 14 is replaced with a dichroic mirror, the space filled with the dichroic prism 54 shown in FIG. 14 is replaced with air, and the viewfinder image on the focusing screen 51 has the same diopter. In order to observe with, the focal length of the eyepiece lens 53 must be made longer than that of the eyepiece lens 53 of FIG.

Since the viewfinder magnification is substantially inversely proportional to the focal length of the eyepiece lens, when the dichroic mirror 67 is used as shown in FIG. 17, the focal length of the eyepiece lens 53 'is longer than that of the eyepiece lens 53 of FIG. As a result, the viewfinder magnification will decrease.

Further, the performance of the finder, for example, the field of view (the ratio of the area that can be recognized by the finder to the photographic screen) and the eye point (the distance from the eyepiece to the observer's eye, that is, no matter how far away the eyepiece is from the eyepiece) The value as shown in FIG. 17 is sacrificed to some extent, and a dedicated pentab rhythm that optimizes the height and the inclination of the line of intersection of the two roof surfaces is used in accordance with this to obtain the configuration shown in FIG. However, it is possible to alleviate the decrease in the viewfinder magnification to some extent.

However, like the dichroic prism, the pentaprism is an optical component having a very complicated processing step and a high manufacturing cost. Therefore, it is necessary to reduce the cost by mass-producing the same shape. If a dedicated pentaprism is used only for a camera that detects the line of sight, the cost of the pentaprism will increase. Therefore, it is difficult to change the pentaprism.

The present invention provides a finder optical system for observing a finder image by utilizing a light beam passing through a light splitting element, and an optical member comprising a lens having a refractive power at a position facing the eyepiece lens with the light splitting element interposed therebetween. It is an object of the present invention to provide a finder optical system capable of observing a good finder image while achieving downsizing by arranging and appropriately setting each element.

[0025]

The finder optical system of the present invention comprises: (a) Observing an object image through an optical member having a refracting power, a plate-like light splitting element, and an eyepiece lens in order from the object side. What I did. (B) After passing through the prism for erecting the object image formed by the photographing lens, an optical member having a refractive power arranged near the exit surface of the prism, a plate-like light splitting element, and an eyepiece lens I tried to observe through. (C) When the focal length of the optical member is f1 and the combined focal length of the optical member and the eyepiece lens is ft, -17.9 <f1 / ft <12.5 is satisfied. (D) When the light flux from the object is guided to the observer's eye through the optical member, the light splitting element, and the eyepiece lens, the focal length of the optical member is f1, and the optical member and the eyepiece lens are combined. -17.9 <f1 / ft <12.5, where ft is the focal length of. (E) The focal length f1 and the combined focal length ft satisfy 1.3 ≦ f1 / ft or f1 / ft ≦ −1.6. (F) The light splitting element splits the light flux incident on the light splitting element into a plurality of different directions. (G) The light flux split by the light splitting element is guided onto the light receiving element by the imaging element to form a light amount distribution. (H) The light splitting element has a spectral characteristic of splitting incident light into visible light and infrared light. (I) The light splitting element is arranged such that the angle formed by the normal line of the light splitting surface of the light splitting element and the optical axis of the eyepiece lens is 45 ° or less. And so on.

[0026]

FIG. 1 is a schematic view of the essential portions of Embodiment 1 in which the finder optical system of the present invention is arranged at a part behind the penta prism of a single-lens reflex camera having a visual axis detection system. In the figure, reference numeral 51 denotes a focusing screen, and a focal plane 51a has a finder image formed by a taking lens (not shown).
52 is an erecting prism, which is a so-called penta prism.

2 is an exit surface 52a of the pentaprism 52.
It is an auxiliary lens (optical member) having a refractive power provided in the vicinity.

Reference numeral 67 denotes a plate-shaped light splitting element (dichroic mirror), which has a light splitting surface 68 that transmits visible light and reflects infrared light.

Reference numeral 1 denotes an eyepiece lens, which is a light flux L from an object.
A is guided to the observer's eyes 501. The eye of the observer 5
In 01, 59 is the cornea, 60 is the iris, and 61 is the pupil.

Reference numeral 58 is a light emitting diode that emits infrared light Lb, 57 is a detection element including an area sensor, and 56 is an imaging lens that guides the infrared light Lb to the detection element 57. Each of these elements 56, 57, 58 constitutes one element of the visual axis detection system.

Infrared light Lb from the light emitting diode 58 illuminates the eyeball 501, is reflected by the eyeball 501, and has a luminous flux La.
The light passes through the eyepiece lens 1 in the opposite direction to and is reflected upward by the light splitting surface 68 of the dichroic mirror 67. And
The imaging lens 56 guides the light to the detection element 57, forms a reflection image of the observer's eye 501 on the light receiving surface of the detection element 57, and obtains eyeball information.

Using the eyeball information obtained from the detecting element 57, the positions of the center of the image of the pupil and the image of the cornea (first Purkinje image) are obtained, and the line of sight of the observer is determined from the relative positional relationship between the two. The direction is being detected.

In this embodiment, after the finder image formed on the focusing screen 51 by the taking lens (not shown) is passed through the pentaprism 52, the exit surface 5 of the pentaprism 52 is shown.
Observation is performed through the optical member 2 arranged in the vicinity of 2b, the dichroic mirror 67, and the eyepiece lens 1.

In this embodiment, as compared with the conventional finder optical system shown in FIG. 17, the optical member 2 is arranged near the exit surface 52b of the pentaprism 52, that is, at a position facing the eyepiece lens 1 with the dichroic mirror 67 interposed therebetween. The points are different, which makes it possible to set the fine day magnification and the eye point distance to desired values.

Next, the optical configurations of the conventional example shown in FIGS. 14 and 17 and the present example will be described in comparison with reference to FIGS.

FIG. 2 is an explanatory view schematically showing the power arrangement of the finder optical system of FIG. In the figure, 3 is shown in FIG.
The focal planes 51a and 4 of the focusing plate 51 of No. 4 are exit surfaces 52 of the pentaprism 52 when the optical path length of the light flux La is converted into air.
Reference numerals b and 5 correspond to the thinned eyepiece lens 53, respectively.

Reference numeral 6 denotes an object point on the focal plane 3 at the outermost periphery of the field of view, which is separated from the optical axis 11 by h1, and 7 denotes a point at the height h2 farthest from the optical axis 11 through which the light beam La can pass on the exit surface 4. Shows.

In the figure, when the light beam La from the object is shown paraxially, among the light rays emitted from the object point 6, the light ray 8 passing through the center of the eyepiece lens 5 goes straight, and the light ray 9 passing through the point 7 is The light is refracted by the eyepiece lens 5 and becomes a light ray 10.

In the finder optical system, the refractive power of the eyepiece lens is generally set so that a virtual image of an object can be observed at a diopter of -1 diopter. That is, the light ray 10 is refracted so as to intersect with the light ray 8 about 1 m ahead when viewed from the observer side.

The values indicating the specifications of the finder optical system include the eye point and the finder magnification. In FIG. 2, the distance d1 of the point 12 at which the light beam 10 intersects the optical axis 11 from the eyepiece 5 corresponds to the eye point. And ray 1
A value obtained by dividing the tangent (tan θ1) of the angle θ1 formed by 0 and the optical axis 11 by h1 is a value proportional to the finder magnification.

Similar to FIG. 2, FIG. 3 schematically shows the power arrangement of the finder optical system of FIG.

In this figure, as compared with FIG. 2, since the dichroic mirror 67 is used instead of the dichroic prism 54 as the light splitting element, the optical path length after the exit surface 4 is long and the eyepiece lens 13 is formed. It is located at the rear.

Therefore, as shown in FIG. 3, the distance d2 and the angle θ2 are as follows: d2 <d1 (1) θ2 <θ1 (2), and the eyepoint distance is shorter than that in FIG. The viewfinder magnification will decrease.

As described above, in the configurations shown in FIGS. 2 and 3, when the positions of the eyepieces 5 and 13 are determined, the refractive power of the eyepieces is determined by the condition that observation is performed at a diopter of -1 diopter. It can be said that there is no freedom to change the design of finder specifications such as finder magnification.

On the other hand, in the present embodiment, as shown in FIG. 1, the optical member 2 is arranged immediately after the pentaprism 52 to set the eyepoint and the finder magnification to desired values.

FIG. 4 is an explanatory view schematically showing the power arrangement of this embodiment. In the figure, reference numeral 15 shows the optical member 2 of FIG. 1 with a reduced thickness, which has a negative refractive power. Similarly, 16 corresponds to the eyepiece 1 of FIG.
Reference numerals 18 respectively show first and second principal planes when the optical member 15 and the eyepiece lens 16 are combined.

In this embodiment, the auxiliary lens 15 is a negative lens and the eyepiece lens 16 is a positive lens.
Two principal planes 17 and 18 defined by one lens are both on the right side of the eyepiece lens 16. Therefore, a point 20 where the light ray 19 emitted from the eyepiece lens 16 intersects the optical axis 11
Also, the eye point distance d3 and the angle θ3 relating to the viewfinder magnification are further shifted to the right side, and θ3 <θ2 ‥‥‥‥‥‥ (3) d3 ≈ d1> d2 ・ ・ ・ (4) ) Relationship.

That is, despite using the dichroic mirror 67 as the light splitting element, it is possible to set the eye point distance to approximately the same level as in FIG.

FIG. 5 is an explanatory view schematically showing the power arrangement of the second embodiment of the present invention, which is different from the first embodiment of FIG. 4 in that the optical member is a positive lens, and other configurations are substantially the same. Is.

In the figure, reference numerals 23 and 24 denote first and second principal planes determined by the optical member 21 and the eyepiece lens 22, respectively.

In this embodiment, the first and second principal planes exist between the optical member 21 and the eyepiece lens 22. Therefore, values d4 and θ4 related to eye point distance and viewfinder magnification
Compared with FIGS. 2 and 3, the relationship of θ4 ≈ θ1> θ2 (5) d4 <d2 ... (6) is established. That is, it is possible to set the viewfinder magnification to approximately the same as in FIG.

As described above, the eye point in Example 1 and the finder magnification in Example 2 were set to the same level as in FIG. 2, but by changing the relationship of the refractive power between the optical member and the eyepiece, It is also possible to set other desired states. Next, this relationship will be described in detail with reference to FIGS.

FIG. 6 shows the positions of the first and second principal planes when the refractive power of the optical member and the combined refractive power of the optical member and the eyepiece are changed in the same configuration as in FIG. FIG.

In the figure, the vertical axis indicates the refracting power φ1 of the optical member 2 and the refracting power φ2 of the eyepiece 1, and the optical member 2
The horizontal axis represents the distance from to the eyepiece 1 direction, and the positions of the first main plane and the second main plane at this time are shown by a solid line and a broken line, respectively.

However, each element shown in FIGS. 4 and 5 is assumed as follows. The height of the object point 6 at the outermost periphery of the visual field on the focal plane 3 is h1, and the height of the point 7 farthest from the optical axis on the exit surface 4 of the pentaprism where the light rays can pass is h2.
The air-equivalent optical path length from the focal plane 3 to the exit surface 4 of the pentaprism is e1, the distance from the exit surface 4 of the pentaprism to the positions 15 and 21 of the optical member is e2, and the position 1 of the optical member is 1.
The distance between 5, 21 and the eyepiece position 16, 22 is e3
Then, as a standard value, h1 = 20.0 mm h2 = 8.3 mm e1 = 59.0 mm e2 = 1.0 mm e3 = 15.0 mm ‥‥‥‥‥‥‥‥‥‥ 7) The refracting power φ2 of the eyepiece lens is determined so that the finder diopter becomes −1 diopter. Therefore, in the figure, the refractive power φ1 is the vertical axis (left side).
, The refractive power φ2 takes a value on the vertical axis (right side).

In the figure, 0 mm indicated by the one-dot chain line on the horizontal axis,
An optical member 2 and an eyepiece lens 1 are arranged at a position of 15 mm, respectively.

According to FIG. 6, as the refracting power φ1 of the optical member 2 decreases from a positive value to a negative value, the two principal points move backward. This is the optical member 2
And that the finder magnification tends to decrease and the eye point distance tends to extend as the configuration of the eyepiece lens 1 is changed to convex, concave, convex, and concave.

FIG. 7 is an explanatory diagram showing changes in the eye point and the finder magnification when the refractive power φ1 is changed. In the figure, the vertical axis represents the refractive power φ1, and the horizontal axis represents the eye point (lower scale) and the viewfinder magnification (upper scale).

In the figure, the solid line shows the eye point and the broken line shows the finder magnification. Note that the finder magnification is a value for a standard lens having a focal length of 50 mm, which is a general value according to the custom of a 35 mm single-lens reflex camera.

This is shown in FIG.
The angle θ (θ1 to θ4 in each figure) formed by the light rays emitted from the eyepieces 16 and 22 shown in FIG. 5 and the height h1 of the object point 6 on the focal plane 3 were calculated by the following equation. It is a thing.

Γ = tan θ / (h1 / 50) (8) FIG. 7 more clearly shows the contradictory relationship between the eye point and the finder magnification.

Here, for comparison, the optical member 2 in FIG.
The optical member 2 occupies a space of 2 mm in the optical axis direction, the dichroic mirror 67 and the eyepiece lens 1 are brought closer to the pentaprism side by the amount of the space, and other configurations are substantially the same as those in FIG. Similarly, when the eye point d and the finder magnification γ of the system (hereinafter, Comparative Example 1) are obtained, d = 20.1 (9) γ = 0.662 (10) The eye point d and the viewfinder magnification γ are
FIG. 8 shows points A and B in the same figure as FIG. 7, respectively.
Is.

In this embodiment, the refracting powers φ1 of the optical members 15 and 21 corresponding to these points A and B are set to φA and φB.
Then, φA = −0.0007 (11) φB = 0.001 (12) Therefore, when the refractive power φ1 of the optical members 15 and 21 is in the range of φA ≦ φ1 ≦ φB (13), it can be said that the effect of using the optical members is small. That is, in the present embodiment, it is desirable that the refracting power φ1 of the optical member takes a value of φ1 <−0.0007 (14) φ1> 0.001 (15). Furthermore, the refractive power of the optical member φ1
When the above are conditional expressions (11) and (12), the combined refractive powers φt with the eyepiece lens are 0.0122 and 0.0125, respectively. Therefore, when normalized by φt, conditional expressions (14) and (15) are It is expressed as follows.

Φ1 / φt <−0.057 (16) φ1 / φt> 0.08 (17) This is because the focal length of the optical member is f1, and the combined focal length of the optical member and the eyepiece lens is ft. Then, -17.9 <f1 / ft <12.5 (18) is expressed.

Since the minimum eye point distance required for a normal single-lens reflex camera is about 13 mm and the viewfinder magnification is about 0.6, the range of the corresponding refracting power φ1 is about −0.007 ≦. φ1 ≦ 0.011 (19) If this is normalized by the combined focal length ft and expressed in the same way as the conditional expression (18), then f1 / ft ≤ -1.6 ... (20) f1 / ft ≥ 1.3 ... (21) By satisfying these ranges, the present embodiment can be used more effectively.

As the material of the optical member and the eyepiece lens, glass is usually most commonly used, but in addition, resins such as acrylic, polycarbonate, polystyrene, or a copolymer of acrylic and polystyrene are preferably used. To be

Next, numerical examples of the present invention will be shown. 9 and 10 are sectional views of lenses of Numerical Embodiments 1 and 2, and FIG.
1 and 12 are aberration diagrams of Numerical Examples 1 and 2, respectively.

In each numerical example, Ri is the radius of curvature of the i-th lens surface in order from the object side, Di is the i-th lens thickness and air gap from the object side, and Ni and νi are respectively i-th order from the object side. The refractive index and Abbe number of the glass of the th lens.

Numerical Example 1 Focal length of whole system ft = 76.19 D 0 = 4.5 R 1 = ∞ D 1 = 82.64 N 1 = 1.51633 ν 1 = 64.1 R 2 = ∞ D 2 = 0.70 R 3 = 107.13 D 3 = 1.5 N 2 = 1.49171 ν 2 = 57.4 f 1 = 250.0 R 4 = 829.78 D 4 = 13.85 R 5 = 50.65 D 5 = 3.00 N 3 = 1.49171 ν 3 = 57.4 N 3 = 103.0 R 6 = ∞ f1 / ft = 3.28 <Numerical Example 2> Focal length of entire system ft = 91.15 D 0 = 4.5 R 1 = ∞ D 1 = 82.64 N 1 = 1.51633 ν 1 = 64.1 R 2 = ∞ D 2 = 0.70 R 3 = 37.15 D 3 = 1.5 N 2 = 1.49171 ν 2 = 57.4 f 1 = -300.0 R 4 = 29.28 D 4 = 18.99 R 5 = 36.09 D 5 = 3.00 N 3 = 1.49171 ν 3 = 57.4 N 3 = 73.4 R 6 = ∞ f1 / ft = 3.29 The case where the present invention is applied to the viewfinder optical system of a single-lens reflex camera has been described above. However, the present invention is not limited to this, and if the configuration is such that an auxiliary lens is arranged facing the eyepiece lens with a light splitting element interposed therebetween, the lens Can be applied to shutter cameras, video cameras, and finder optical systems such as various measuring instruments Is.

Further, the present invention is not limited to the finder optical system using the light splitting element for detecting the line of sight, but may be a finder optical system used for focus detection or exposure control, for example.

In the first embodiment shown in FIG. 1, the angle Δ1 formed by the normal line of the dichroic mirror 67 and the optical axis 11 is 4
Although it is set to 5 °, the angle Δ2 formed by the two is 45 as shown in FIG.
The angle may be smaller than 0 ° and the dichroic mirror 67 may be arranged to be more vertical. In this way, the distance between the optical member 2 and the eyepiece lens 1 can be narrowed, which is advantageous in extending the eyepoint distance and increasing the finder magnification.

In the present invention, the erecting prism is not limited to the pentaprism shown in the above embodiment, but may be a Porro prism or the like as long as it reflects or deflects so that the observer can correctly observe the finder image. A prism may be used.

[0073]

According to the present invention, in a finder optical system having a light splitting element, an optical member is arranged at a position facing the eyepiece lens with the light splitting element sandwiched therebetween, and by appropriately setting each element, It is possible to achieve a viewfinder optical system that enables good observation of a viewfinder image while achieving miniaturization.

[Brief description of drawings]

FIG. 1 is a schematic view of a main part of a first embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a power arrangement of a conventional finder optical system.

FIG. 3 is an explanatory view showing a power arrangement of a conventional finder optical system.

FIG. 4 is an explanatory diagram showing a power arrangement according to the first embodiment of the present invention.

FIG. 5 is an explanatory diagram showing a power arrangement according to a second embodiment of the present invention.

FIG. 6 is an explanatory diagram showing the positions of the first and second principal planes when the refracting powers of the auxiliary lens and the eyepiece lens are changed.

FIG. 7 is an explanatory diagram showing changes in eye point and finder magnification when the refractive power φ1 is changed.

8 is an explanatory view showing a refractive power φ1 corresponding to Comparative Example 1. FIG.

FIG. 9 is a lens cross-sectional view of Numerical Example 1 of the present invention.

FIG. 10 is a lens cross-sectional view of Numerical Example 2 of the present invention.

FIG. 11 is a diagram showing various types of aberration in Numerical Example 1 of the present invention.

FIG. 12 is a diagram showing various types of aberration in Numerical Example 2 of the present invention.

FIG. 13 is a schematic view of an essential part of the present invention.

FIG. 14 is a schematic view of a main part of a conventional finder optical system.

FIG. 15 is an explanatory diagram showing a reflected image of an observer's eye formed on the light receiving element surface.

FIG. 16 is a schematic view of a main part of a conventional finder optical system.

FIG. 17 is a schematic view of a main part of a conventional finder optical system.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Eyepiece lens 2 Auxiliary lens 51 Focus plate 52 Penta-dach prism 56 Imaging lens 57 Light receiving element 58 Light emitting diode 59 Corneal 60 Iris 61 Pupil 67 Dichroic mirror 68 Light splitting surface d d line g g line ΔM Meridional image plane ΔS sagittal image plane

Claims (9)

[Claims] 1. A finder optical system characterized in that an object image is observed through an optical member having a refracting power, a plate-like light splitting element, and an eyepiece lens in order from the object side. 2. An optical member having a refracting power, which is arranged in the vicinity of the exit surface of the prism after passing an object image formed by a taking lens through an erecting prism, and a flat light splitting element, and A finder optical system characterized by being observed through an eyepiece lens. 3. When the focal length of the optical member is f1 and the combined focal length of the optical member and the eyepiece lens is ft, -17.9 <f1 / ft <12.5 is satisfied. The finder optical system according to claim 1 or 2. 4. When a light beam from an object is guided to an observer's eye through an optical member, a light splitting element and an eyepiece lens, the focal length of the optical member is f1, the optical member and the eyepiece lens are The finder optical system is characterized in that -17.9 <f1 / ft <12.5 is satisfied, where ft is the combined focal length of the above. 5. The focal length f1 and the combined focal length ft satisfy 1.3 ≦ f1 / ft or f1 / ft ≦ −1.6. Viewfinder optical system. 6. The finder optical system according to claim 1, wherein the light splitting element splits the light flux incident on the light splitting element into a plurality of different directions. 7. The finder optical system according to claim 1, wherein the light flux split by the light splitting element is guided by an imaging element onto a light receiving element to form a light amount distribution. . 8. The finder optical system according to claim 1, wherein the light splitting element has a spectral characteristic of splitting incident light into visible light and infrared light. 9. The light splitting element is arranged such that an angle formed by a normal line of a light splitting surface of the light splitting element and an optical axis of the eyepiece lens is 45 ° or less. Item 1, 2, 3 or 4 finder optical system.