CN113646684A

CN113646684A - Optical viewfinder and camera

Info

Publication number: CN113646684A
Application number: CN201980094954.4A
Authority: CN
Inventors: 陈媛; 毛庆
Original assignee: SZ DJI Technology Co Ltd
Current assignee: SZ DJI Technology Co Ltd
Priority date: 2019-12-31
Filing date: 2019-12-31
Publication date: 2021-11-12
Also published as: WO2021134707A1

Abstract

A camera (10) and an optical viewfinder (15), the optical viewfinder (15) comprising, in order from an object side to a human eye side in an optical axis direction: a first lens element (L1) with negative refractive power, the side surface (S2) of the first lens element (L1) facing the human eye being concave; a second lens element (L2) with refractive power, wherein the side surface (S4) of the second lens element (L2) facing the human eye is concave; a third lens element (L3) with refractive power; the fourth lens (L4) has positive refractive power and a four-lens structure, has a compact overall structure, is convenient to realize miniaturization, and can meet the view finding requirement of a large wide angle due to reasonable matching of refractive power and surface shape.

Description

Optical viewfinder and camera

Technical Field

The present application relates to the field of viewfinder technology, and in particular, to an optical viewfinder and a camera.

Background

Current view finder is mostly electronic view finder, consumes the fuselage electric quantity in the use, shortens the fuselage live time, and there is the colour noise point problem in part display screen, influences the use impression. In order to overcome the defects of the electronic viewfinder, an optical viewfinder is provided, however, the existing optical viewfinder is mostly used for adapting a focal length lens of 25mm or more, and the viewfinder for adapting a wide-angle lens is fewer.

Disclosure of Invention

It is an object of the present application to provide an optical viewfinder and a camera that can solve the above-described problems.

In order to achieve the purpose of the application, the application provides the following technical scheme:

in a first aspect, an embodiment of the present application provides an optical viewfinder, sequentially including, from an object side to a human eye side in an optical axis direction: the first lens element with negative refractive power has a concave side surface for human eyes; the second lens has refractive power, and the side surface of the human eye of the second lens is a concave surface; a third lens element with refractive power; the fourth lens element with positive refractive power.

In a second aspect, an embodiment of the present application provides an optical viewfinder, sequentially including, from an object side to a human eye side in an optical axis direction: a first lens element with negative refractive power; a second lens having a negative bending force; the third lens element with positive refractive power.

In a third aspect, embodiments of the present application provide a camera, including the optical viewfinder of any one of the various embodiments of the first and second aspects.

The structure of four lens of this application embodiment, overall structure is compact, is convenient for realize the miniaturization, and simultaneously, the configuration of reasonable refractive power and face type can satisfy the demand of finding a view of big wide angle.

Drawings

FIG. 1 is a schematic diagram of a camera according to an embodiment;

FIG. 2 is a schematic diagram of an optical viewfinder according to an embodiment;

FIG. 3 is a schematic structural view of a marker of an embodiment;

FIG. 4 is a longitudinal spherical aberration diagram of an embodiment of an optical viewfinder at infinity scene sharp imaging state;

fig. 5 is an astigmatism curve and a distortion curve in a clear imaging state of an infinite scene of an optical viewfinder according to an embodiment.

DETAILED DESCRIPTION OF EMBODIMENT (S) OF INVENTION

The technical solutions in the embodiments of the present application will be described below clearly with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are only a part of the embodiments of the present application, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.

It will be understood that when an element is referred to as being "secured to" another element, it can be directly on the other element or intervening elements may also be present. When a component is referred to as being "connected" to another component, it can be directly connected to the other component or intervening components may also be present.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein in the description of the present application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.

Some embodiments of the present application will be described in detail below with reference to the accompanying drawings. The embodiments described below and the features of the embodiments can be combined with each other without conflict.

Referring to fig. 1, an embodiment of the present application provides a camera 10, where the camera 10 includes a housing 11, a shutter 13, a lens 14, and an optical viewfinder 15 provided in an embodiment of the present application. The camera 10 in some embodiments may also include a display screen 12. The display 12, the shutter 13, and the lens 14 are disposed in the housing 11. The optical viewfinder 15 may be provided on the top and side of the housing 11, or may be integrated within the housing 11. The housing 11 is provided therein with an optical sensor and a processor, the optical sensor is used for receiving the light entering from the lens 14 and forming an electrical signal of the light on a photosensitive surface of the optical sensor, and the processor processes the electrical signal to obtain a digital photo. The display 12 is used to display the digital photos, and in some embodiments, the display 12 can also be used to view, i.e. real-time images of the light entering from the lens 14 are fed back to the display 12 for display. The shutter 13 is used to control the time for which light is irradiated to the optical sensor, i.e., the effective exposure time of the optical sensor. The lens 14 is used for receiving the optical light, bending, refracting and the like the light to a certain degree, changing the path of the light, and meeting the use of a plurality of focal sections such as wide angle, standard and long focus. The lens 14 may be built in the housing 11, or may be externally attached and detachably connected to the housing 11. The optical finder 15 is a structure for monitoring an image through an eyepiece on the camera 10. The optical viewfinder 15 in the embodiment of the present application may be a general optical viewfinder through which light does not pass through the lens 14, and is widely used in a digital camera for home use, such as a card-type digital camera; the optical viewfinder 15 may be a complicated optical viewfinder through which light passes from the lens 14, and generally, a structure such as a mirror and a pentaprism is provided in the housing 11, and light entering from the lens enters the optical viewfinder through reflection, refraction, and the like, and is mainly applied to professional digital cameras, such as single lens reflex digital cameras. It is to be understood that the optical viewfinder 15 in the embodiment of the present application can also be applied to a mechanical camera, and is not limited to an electronic digital camera.

At present, a conventional optical viewfinder is generally only used in a lens with a focal length greater than 25mm, when the focal length is shorter and less than 25mm, the optical viewfinder which is adapted to a focal length less than 25mm is less, and the image distortion seen by the optical viewfinder greater than 25mm cannot meet the requirement. The optical viewfinder 15 provided in the embodiment of the present application can satisfy large wide-angle framing. When the lens is matched with a lens with a large wide angle for use, the effect is better.

The following describes an optical viewfinder provided by an embodiment of the present application.

Referring to fig. 2, an embodiment of the present application provides an optical viewfinder, the optical viewfinder sequentially including, from an object side to an eye side along an optical axis direction: a first lens L1, a second lens L2, a third lens L3, and a fourth lens L4.

The first lens element L1 with negative refractive power has a concave eye-side surface S2 of the first lens element L1; the second lens element L2 with negative refractive power has a concave eye-side surface S4 of the second lens element L2; the third lens element L3 has refractive power; the fourth lens element L4 has positive refractive power.

In this embodiment, the second lens element L2 with positive refractive power can also have positive refractive power, and the third lens element L3 with positive or negative refractive power can also have positive or negative refractive power.

In one embodiment, the object-side surface S1 of the first lens element L1 is convex; the object-side surface S3 of the second lens element L2 is convex; the object side S5 of the third lens L3 is convex, and the eye side S6 is concave; the human eye-side surface S8 of the fourth lens L4 is convex.

In other words, along the optical axis from the object side to the human eye side, the surface types of the object side surface and the human eye side surface of each lens are respectively: the first lens L1 is convex-concave, the second lens L2 is convex-concave, the third lens L3 is convex-concave, and the fourth lens L4 is convex toward the side of the eye. That is, the lens group formed by the first lens L1 to the third lens L3 can maximize the angle of view, and satisfy the requirement of wide angle, and the fourth lens L4 can refract the light to satisfy the angle of view observed by human eyes, and referring to the path of the light 100 (solid line) of the object in fig. 2, the light 100 of the object is refracted and converged on the human eyes by the action of the first lens L1 to the fourth lens L4. Optionally, each surface is a spherical surface, and compared with an aspheric surface, the spherical surface has the advantages of simple structure, easiness in processing and manufacturing and low cost.

In this embodiment, the object-side surface S7 of the fourth lens element L4 can be a plane, a convex surface or a concave surface, and the object-side surface S7 is a plane.

In one embodiment, referring to fig. 1 and 2, the optical viewfinder 15 further includes a stop STO for controlling the amount of incoming light. In general, the stop STO may be disposed at any position in the optical viewfinder 15, for example, at the object side surface S1 side of the first lens L1, or at a position between four lenses, or at the human eye side surface S8 side of the fourth lens L4. Illustratively, the stop STO is disposed on the side of the human eye side S8 of the fourth lens L4 and approximately coincides with the pupil position of the human eye (which position can be considered to be at the outermost side of the camera 10 proximate to the human eye).

The first lens L1 to the fourth lens L4 may be assembled in an edge contact manner (for example, by adhesive bonding), or may be assembled by being mounted on a support structure such as a lens barrel with a gap between two adjacent lenses without direct contact.

The first lens L1 to the fourth lens L4 may be made of glass or plastic. Illustratively, the first lens L1 and the fourth lens L4 are made of glass. Because the first lens L1 and the fourth lens L4 are located on the outermost side of the lens group, collision can occur at a certain probability, and the glass has higher hardness than plastic, so that scratch defects caused by collision and the like can be reduced. In addition, glass has higher light transmittance than plastic in the light wavelength range sensed by human eyes, and the yellowing degree of images observed by human eyes can be effectively inhibited by adopting the glass. In consideration of the cost, the cost of the glass material is higher than that of the plastic material due to the difference between the glass and the plastic in terms of raw materials, processing difficulty, and the like, and therefore, it is also possible to set only one of the first lens L1 or the fourth lens L4, which is most likely to be collided, as glass, and the other lenses as plastic.

In one embodiment, referring to fig. 2 and 3, any one of the first lens L1 to the fourth lens L4 is provided with a marker 300, and the marker 300 is disposed on the object side or the eye side. Also, the marker 300 may be disposed at any position on the object side or the human eye side, which may be a partially circular region, a rectangular region, an annular region, or the like on the object side or the human eye side. Illustratively, the marker 300 is disposed on a surface of greater radius of curvature in the object side and the eye side. The marker 300 is arranged on the surface with larger curvature radius, so that the processing is convenient. The specific processing technique can adopt processing modes such as film coating, silk screen printing, etching, laser etching and the like to attach the marker 300 to the surface of a certain lens. The color and material of the marker 300 are not limited.

In this embodiment, the radius of curvature of each lens may be: the curvature radius of the object-side surface S1 of the first lens L1 is larger than that of the human eye-side surface S2, the curvature radius of the object-side surface S3 of the second lens L2 is larger than that of the human eye-side surface S4, the curvature radius of the object-side surface S5 of the third lens L3 is larger than that of the human eye-side surface S6, and the curvature radius of the object-side surface S7 of the fourth lens L4 is larger than that of the human eye-side surface S8. Therefore, the marker 300 may be disposed on any one surface of the object side surface S1 of the first lens L1, the object side surface S3 of the second lens L2, the object side surface S5 of the third lens L3, and the object side surface S7 of the fourth lens L4. Illustratively, the marker 300 is disposed on the object-side surface S7 of the fourth lens L4, the object-side surface S7 has a larger radius of curvature than the other lenses, i.e., the object-side surface S7 of the fourth lens L4 is flatter and is easy to process, and in addition, the fourth lens L4 is closer to the human eye and is not easy to be directly imaged by the human eye to cause occlusion.

In one embodiment, the marker 300 includes one or more of the following: the system comprises a single view field wire frame, a plurality of view field wire frames, a focusing prompt wire, a central focusing frame, a central cross wire, wire frame supplementary description information and enterprise marks.

Among them, the field wire frame may be a rectangular wire frame (as indicated by reference numeral 302 in fig. 3), a circular wire frame, or the like, for composition. The plurality of view field wire frames may be a structure in which the plurality of rectangular wire frames are sequentially nested, and a spacing distance is provided between adjacent rectangular wire frames, or the plurality of view field wire frames are a structure in which the plurality of circular wire frames are sequentially nested, and a spacing distance is provided between adjacent circular wire frames, or the plurality of view field wire frames are a structure in which a circle and a rectangle are mixed, and a spacing distance is provided between adjacent view field wire frames. The spaced distance between adjacent two of the plurality of field wire frames may be equal.

The focusing prompt line can be a plurality of lines arranged at intervals, such as a plurality of straight lines arranged transversely and longitudinally, and divides the visual field into a plurality of block-shaped areas, and the intersecting positions of the transverse straight lines and the longitudinal straight lines are used for assisting focusing and composition. The center focusing frame may be a central rectangle with a smaller area for assisting focusing. The center cross (as indicated by reference numeral 301 in fig. 3) has a cross shape for patterning. The wire frame supplementary specification information (as indicated by reference numeral 303 in fig. 3) may be a specific size parameter of the wire frame or the like. The enterprise logo is, for example, an enterprise logo, and can be arranged at any position of the visual field.

The type of marker 300 described above may be singular, such as a single field of view wireframe disposed in the peripheral field of view; the type of marker 300 is preferably arranged in various combinations, for example, as shown in fig. 3, the marker 300 includes a center cross 301, a plurality of field-of-view wire frames 302, and wire frame supplementary descriptive information 303. The single view field wire frame only can be adapted to a single focal length, and the application range is small. Compared with a single view field wire frame, the marker 300 can adapt to a plurality of different focal lengths under the condition of various combinations, and the application range is wider.

The marker 300 is provided on any one of the second lens L2 to the fourth lens L4, any one of the first lens L1 to the third lens L3 which is closer to the object side than the marker 300 has a reflection function, and an image of the marker 300 enters human eyes after being reflected by any one of the first lens L1 to the third lens L3.

Specifically, the marker 300 is disposed on the object side S3 or the eye side S4 of the second lens L2, and the object side S1 or the eye side S2 of the first lens L1 has a reflection function; the marker 300 is disposed on the object side S5 or the eye side S6 of the third lens L3, so that any one of the object side S1 or the eye side S2 of the first lens L1 and the object side S3 or the eye side S4 of the second lens L2 has a reflection function; the marker 300 is disposed on the object side surface S7 or the human eye side surface S8 of the fourth lens L4, and any one of the object side surface S1 or the human eye side surface S2 of the first lens L1, the object side surface S3 or the human eye side surface S4 of the second lens L2, and the object side surface S5 or the human eye side surface S6 of the third lens L3 has a reflection function. In an exemplary embodiment, as shown in fig. 2, the marker 300 is disposed on the object side S7 of the fourth lens L4, and the object side S5 of the third lens L3 has a reflective function. With reference to the optical path (shown by the dotted line) 200 in fig. 2, the light of the marker 300 on the object-side surface S7 of the fourth lens L4 is reflected by the object-side surface S5 of the third lens L3, and enters the fourth lens L4 to enter the human eye. The light of the marker 300 is designed to be reflected and then enter human eyes, but not directly transmitted and then enter human eyes, so that the fact that a proper focal length is needed for forming a clear image on the human eyes is considered, no matter which lens is provided with the marker 300, the distance between the lens and the human eyes is too short, and the direct transmission mode cannot be focused on the human eyes. Thus, by providing the optical path of the reflective marker 300 such that the distance between the marker 300 and the human eye is extended (i.e., the path length of the optical path is extended), an image can be formed on the human eye, and a human can see a clear image of the marker 300.

It should be understood that the location of the marker 300 provided herein should correspond to, and not conflict with, the previously described placement of the marker 300 on a surface having a larger radius of curvature.

The reflection function of the surface of the lens can be realized by various schemes, for example, generally, the lens is coated with an antireflection film in order to increase the light transmittance, and the reflection function can be realized by reducing the light transmittance, i.e. not coating the antireflection film. Or, the lens is plated with the light splitting film, so that part of light can be reflected while part of light is allowed to pass through, and the lens can also have a reflection function. Compared with a scheme of plating a light splitting film without plating an antireflection film, the reflectivity can be adjusted according to needs, and the controllability is higher.

When the scheme of plating the spectroscopic film is adopted, the spectroscopic film covers at least a part of the optical path coverage of the marker 300 on any one of the first lens L3 to the third lens L3. In other words, the surface of the lens where the light splitting film is located has a central area and an edge area, and when the light of the marker 300 enters the lens where the light splitting film is located, the light path covers the central area but does not cover the edge area, so the light splitting film should be at least partially disposed in the central area, so that the light of the marker 300 is at least partially reflected. Of course, the light splitting film may be provided over the entire central region and the entire surface of the lens. Similarly, the partial surface area of the lens with the reflection function may be not coated with the antireflection film, or the whole surface may not be coated with the antireflection film. The effect is to ensure that the surface has a certain reflectivity, allowing the marker 300 to be imaged through the surface. When the light path of the marker 300 passes through the area partially covered by the light splitting film or the antireflection film, the reflectivity of the area covered by the light splitting film or the antireflection film is higher, the visibility is clearer, the reflectivity of the area not covered by the light splitting film or the antireflection film is lower, but the area cannot reflect completely, and the light of the area is slightly dark and can be seen.

In one embodiment, referring to fig. 1 and 2, the optical viewfinder 15 satisfies the following conditional expression: TTL is less than or equal to 30 mm; wherein, TTL is a distance on the optical axis from the object side surface S1 of the first lens L1 to the human eye side surface S8 of the fourth lens L4, i.e., TTL is a total length of the lens assembly of the first lens L1 to the fourth lens L4. Satisfying the above formula, the structure of the optical finder 15 can be miniaturized.

In one embodiment, referring to fig. 1 to 2, the optical viewfinder 15 satisfies the following conditional expression: TAN (A)_i) Not less than 0.85; wherein A is_iIs half of the diagonal field angle of the optical viewfinder 15, TAN (A)_i) Is the field angle A of the optical viewfinder 15_iThe tangent value of (c). In fig. 2, the angle between the maximum angle ray 101 of the object imaged by the optical viewfinder 15 and the optical axis is a_iThe above formula is satisfied, and the wide angle of view of the optical finder 15 can be realized.

In one embodiment, referring to fig. 1 and 2, the optical viewfinder 15 satisfies the following conditional expression:

wherein, c₁Is the surface curvature of the object side S1 of the first lens L1, c₂Is the surface curvature of the human eye side S2 of the first lens L1. In the optical field, the surface curvature has directionality, different directions, the surface curvature can be positive or negative, and c₁-c ₂The difference value of the optical axis is in direct proportion to the focal power of the lens; when the surface curvatures of the object side S1 and the human eye side S2 of the first lens L1 are the same but opposite in direction, the above conditional expression is equal to 0. The above formula is satisfied, so that the aberration of the lens group is in a controllable range under the condition of satisfying the large angle of light incidence.

In one embodiment, referring to fig. 1 and 2, the optical viewfinder 15 satisfies the following conditional expression:28≤V ₂less than or equal to 97; wherein, V₂The abbe number of the second lens L2. When V is₂When the refractive power is less than 28, the chromatic aberration is larger, the pressure of chromatic aberration correction of the whole lens group is increased, the requirement on a lens with positive refractive power is higher, and the selection of materials is limited. When V is₂If the amount is more than 97, the cost of the material is greatly increased. Therefore, the formula is satisfied, the color difference is in a proper range, and the material cost is low.

In one embodiment, referring to fig. 1 and 2, the optical viewfinder 15 satisfies the following conditional expression: 0.0184V₄+N ₄Less than or equal to 2.5; wherein, V₄Abbe of the fourth lens L4, N₄Is the refractive index of the fourth lens L4. When 0.0184V₄+N ₄When the refractive power is larger than 2.5, the fourth lens element L4 has a poor chromatic aberration correction capability, and the material of the lens element having negative refractive power in the optical viewfinder 15 is limited. Satisfying the above formula, the chromatic aberration correction capability of the fourth lens element L4 is better, and the limitation on the material of the lens element with negative refractive power in the optical viewfinder 15 is small.

Table 1 is overall parameter information of the optical viewfinder of one embodiment.

TABLE 1

Object space diagonal angle of view (°)	±49.5
Human eye perception field angle (°)	±21.54
Magnification factor	0.34

Table 2 is data information of each surface of the optical viewfinder of one embodiment.

TABLE 2

Flour mark	R	D	N	V
Article surface	Infinite number of elements	Infinite number of elements
S1	24.510	1.200	1.75	52.30
S2	10.185	3.675
S3	27.884	1.000	1.62	63.40
S4	11.610	3.428
S5	23.170	1.000	1.80	40.00
S6	13.587	8.644
S7	Infinite number of elements	7.000	1.75	35.00
S8	-17.378	15.000
STO	Infinite number of elements	-

In table 2, R represents a curvature radius in mm, D represents an on-axis distance in mm, N represents a refractive index, and V represents an abbe number. Stop STO coincides with the position of the pupil of the human eye.

Referring to the longitudinal spherical aberration graph of FIG. 4, spherical aberration occurs with respect to line C, line d and line F, the wavelength of line C is 656.3nm, the wavelength of line d is 587.6nm, the wavelength of line F is 486.1nm, and the spherical aberration is within a controllable range.

Referring to the astigmatism curves and distortion curves of fig. 5, in the astigmatism curves, the solid line represents the aberration relative to the sagittal image plane, and the dashed line represents the aberration relative to the meridional image plane. It can be seen that both astigmatism and distortion are in a controllable range.

As can be seen from fig. 4 and 5, the optical viewfinder according to the embodiment of the present application has a good optical quality.

Under the same inventive concept, the present application provides another optical viewfinder, wherein an optical axis direction sequentially includes, from an object side to a human eye side: a first lens element with negative refractive power; a second lens having a negative bending force; a third lens element with positive refractive power. Different from the previous embodiment, the present embodiment adopts three lenses, which can also achieve compact structure and miniaturization, and can meet the view finding requirement of large wide angle.

In one embodiment, any one of the first lens to the third lens is provided with a marker, and the marker is arranged on the object side or the human eye side and can be positioned at any position. Illustratively, the marker is disposed on a surface of the object side or eye side having a larger radius of curvature. This part is limited to the description in the foregoing embodiments and can be appropriately transferred to the structure of three lenses, which is not described again.

In one embodiment, the marker is attached to the object side or the human eye side by any one of plating, screen printing, etching and laser etching.

In one embodiment, the marker comprises one or more of the following: the system comprises a single view field wire frame, a plurality of view field wire frames, a focusing prompt wire, a central focusing frame, a central cross wire, wire frame supplementary description information and enterprise marks. Reference is made to the foregoing description for brevity.

In one embodiment, the field of view wire frames are rectangular, and when the marker is a plurality of field of view wire frames, the plurality of field of view wire frames are in a sequentially nested structure.

In one embodiment, the mark member is disposed on the second lens or the third lens, and the first lens or the second lens closer to the object side than the mark member has a reflection function, and an image of the mark member enters the human eye after being reflected by the first lens or the second lens.

In one embodiment, the object side surface or the eye side surface of the first lens or the second lens closer to the object side than the marker has a reflection function is not coated with an antireflection film or is coated with a light splitting film with a preset reflectivity.

In one embodiment, the marker is disposed on the third lens, and the object-side surface of the second lens has a reflective function.

In one embodiment, the area of the light splitting film is larger than or equal to the area of the mark part in the light path coverage area of the first lens or the second lens.

In one embodiment, the first lens and/or the third lens is made of glass.

In one embodiment, the optical viewfinder satisfies the conditional expression: TTL is less than or equal to 30; wherein, TTL is the distance on the optical axis from the object side surface of the first lens to the human eye side surface of the fourth lens.

In one embodiment, the optical viewfinder satisfies the conditional expression: TAN (A)_i) Not less than 0.85; wherein A is_iIs half of the diagonal field angle of the optical viewfinder, TAN (A)_i) For the field angle A of the optical viewfinder_iThe tangent value of (c).

In one embodiment, the optical viewfinder satisfies the conditional expression:

wherein, c₁Is the surface curvature of the object side of the first lens, c₂Is the surface curvature of the human eye side of the first lens.

The present application has been described in detail above, and the principles and embodiments of the present application have been described herein using specific examples, which are provided only to help understand the method and the core concept of the present application; meanwhile, for a person skilled in the art, according to the idea of the present application, there may be variations in the specific embodiments and the application scope, and in summary, the content of the present specification should not be construed as a limitation to the present application.

Claims

An optical viewfinder, characterized by comprising, in order from an object side to a human eye side in an optical axis direction:

the first lens element with negative refractive power has a concave side surface for human eyes;

the second lens has refractive power, and the side surface of the human eye of the second lens is a concave surface;

a third lens element with refractive power;

the fourth lens element with positive refractive power.
The optical viewfinder of claim 1, wherein the second lens element has a negative refractive power.
The optical viewfinder of claim 2,

the object side surface of the first lens is a convex surface;

the object side surface of the second lens is a convex surface;

the object side surface of the third lens is a convex surface, and the side surface of a human eye is a concave surface;

the human eye side surface of the fourth lens is a convex surface.
The optical finder as claimed in any of claims 1 to 3, wherein any of said first lens to said fourth lens is provided with a marker provided on an object side or a human eye side.
The optical viewfinder of claim 4 wherein said marker is disposed on a surface of greater radius of curvature of said object side surface and said eye side surface.
The optical viewfinder of claim 4 or 5, wherein the mark member is provided on the fourth lens.
The optical finder as claimed in any of claims 4 to 6, wherein said mark member is provided at an arbitrary position on the object side or the human eye side.
The optical viewfinder of claim 4, wherein said marking element is attached to said object side or said eye side by any of plating, screen printing, etching, or laser engraving.
The optical viewfinder of claim 4, wherein the indicia include one or more of: the system comprises a single view field wire frame, a plurality of view field wire frames, a focusing prompt wire, a central focusing frame, a central cross wire, wire frame supplementary description information and enterprise marks.
The optical viewfinder of claim 9, wherein the field wire frame is rectangular, and when the marker is a plurality of field wire frames, the plurality of field wire frames are in a sequentially nested configuration.
The optical viewfinder of claim 4, wherein the mark member is provided on any one of the second lens to the fourth lens, any one of the first lens to the third lens closer to the object side than the mark member has a reflection function, and an image of the mark member enters the human eye after being reflected by any one of the first lens to the third lens.
The optical viewfinder of claim 11, wherein any one of the object side surface or the eye side surface of the first lens to the third lens having a reflective function, which is closer to the object side than the mark member, is not coated with an antireflection film or is coated with a predetermined-reflectivity splitting film.
The optical viewfinder of claim 12 wherein said marker is disposed on said fourth lens, and an object side surface of said third lens has a reflective function.
The optical viewfinder of claim 12, wherein an area of the light splitting film is equal to or larger than an area of an optical path coverage of the mark member on any one of the first lens to the third lens.
The optical viewfinder of claim 1, wherein the material of the first lens element and/or the fourth lens element is glass.
The optical finder of any one of claims 1 to 15, wherein the optical finder satisfies a conditional expression:

TTL≤30mm

wherein, TTL is the distance on the optical axis from the object side surface of the first lens to the human eye side surface of the fourth lens.
The optical finder of any one of claims 1 to 15, wherein the optical finder satisfies a conditional expression:

TAN(A _i)≥0.85

wherein A is_iIs half of the diagonal field angle of the optical viewfinder, TAN (A)_i) For the field angle A of the optical viewfinder_iThe tangent value of (c).
The optical finder of any one of claims 1 to 15, wherein the optical finder satisfies a conditional expression:

wherein, c₁Is a stand forSurface curvature of object side surface of the first lens, c₂Is the surface curvature of the human eye side of the first lens.
The optical finder of any one of claims 1 to 15, wherein the optical finder satisfies a conditional expression:

28≤V ₂≤97

wherein, V₂Is the abbe number of the second lens.
The optical finder of any one of claims 1 to 15, wherein the optical finder satisfies a conditional expression:

0.0184*V ₄+N ₄≤2.5

wherein, V₄Is the Abbe number, N, of the fourth lens₄Is the refractive index of the fourth lens.
An optical viewfinder, characterized by comprising, in order from an object side to a human eye side in an optical axis direction:

a first lens element with negative refractive power;

a second lens having a negative bending force;

the third lens element with positive refractive power.
The optical viewfinder of claim 21, wherein any of the first lens through the third lens is provided with a marker provided on an object side or a human eye side.
The optical viewfinder of claim 22 wherein said marker is disposed on a surface of greater radius of curvature of said object side surface and said eye side surface.
The optical viewfinder of claim 22 or 23, wherein the mark member is disposed on the third lens.
The optical viewfinder of any of claims 22-24, wherein the marker is disposed at any position on the object side or the eye side.
The optical viewfinder of claim 22, wherein said marking element is attached to said object side or said eye side by any of plating, screen printing, etching, or laser engraving.
The optical viewfinder of claim 22, wherein the indicia include one or more of: the system comprises a single view field wire frame, a plurality of view field wire frames, a focusing prompt wire, a central focusing frame, a central cross wire, wire frame supplementary description information and enterprise marks.
The optical viewfinder of claim 27, wherein the field wire frame is rectangular, and when the marker is a plurality of field wire frames, the plurality of field wire frames are in a sequentially nested configuration.
The optical viewfinder of claim 22, wherein the mark member is disposed on the second lens or the third lens, and the first lens or the second lens closer to the object side than the mark member has a reflection function, and an image of the mark member enters the human eye after being reflected by the first lens or the second lens.
The optical viewfinder of claim 29, wherein an object side or a human eye side of the first lens or the second lens having a reflection function, which is closer to an object side than the mark member, is not coated with an antireflection film or a predetermined reflectance splitting film.
The optical viewfinder of claim 30, wherein the mark member is disposed on the third lens, and an object side surface of the second lens has a reflective function.
The optical viewfinder of claim 30, wherein an area of the light splitting film is equal to or larger than an area of the mark member covering an optical path of the first lens or the second lens.
The optical viewfinder of claim 21, wherein the material of the first lens element and/or the third lens element is glass.
The optical finder of any one of claims 21 to 33, wherein the optical finder satisfies a conditional expression:

TTL≤30

wherein, TTL is the distance on the optical axis from the object side surface of the first lens to the human eye side surface of the fourth lens.
The optical finder of any one of claims 21 to 33, wherein the optical finder satisfies a conditional expression:

TAN(A _i)≥0.85

wherein A is_iIs half of the diagonal field angle of the optical viewfinder, TAN (A)_i) For the field angle A of the optical viewfinder_iThe tangent value of (c).
The optical finder of any one of claims 21 to 33, wherein the optical finder satisfies a conditional expression:

wherein, c₁Is the surface curvature of the object side of the first lens, c₂Is the surface curvature of the human eye side of the first lens.
A camera characterized by comprising the optical finder as claimed in any one of claims 1 to 36.