Focus detector of camera

[Detailed Description of the Invention]

Technical field The present invention relates to the focus detecting device of the camera which receives the light which penetrated the photographing lens and performs focal detection of the photographing lens. Conventional technology Arrangement ■ Conventionally, various focus detecting devices like Above are known, arrange a condensing lens behind the schedule Phone side of a photographing lens one of them, and it makes one pair of imaging lenses optic-axis symmetry behind the condensing lens, It is in some which compare the image of the schedule focal plane formed, respectively, and perform focal detection of a photographing lens with both the Statue lens. Drawing 1 shows the basic optical system of such a focus detecting device, and (the '1 ground) is a photographing lens, (Lo) is [ a condensing lens, (Ll) and (L2) ] imaging lenses, respectively, Both Statue lens (Ll) (L2) becomes symmetrical to optic-axis (X) of a photographing lens ('l''L), and the optic axis of both the Statue lens (Ll) and (L2) is Distribution(ed), respectively so that it may become optic-axis (X) and parallel. (F) is schedule focus m1 of a photographing lens (TL), and (ljR) is an imaging surface of both the Statue lens. To a single photographic subject, when it is in a photographing lens or a focus state, the image (8) is formed on schedule focal 1111CF by such composition, and also the l-th image (A1) and the 2nd image (A2) are formed of an imaging lens (Ll) and (B-2). And when a photographing lens (T L) is in a back pin state, the image (B) is back formed from the image at the time of a focus (A) -- " -- further -- imaging lens (Ll) -- the l-th image (B+) and the 2nd image (B-2) are formed in the direction more nearly perpendicular to optic-axis (X) than the 2nd image (A2) of the 1st image (A1) at the time of a focus of (B-2) in 1iil[Was done position ", respectively. Conversely, an image (C) is ahead formed from the image at the time of a focus (A) of photography Wren X' ('l''L) in a front pin state, and it is the 1st [ the ] (formed in the position near [ time / of a focus ] optic-axis (X) both m and and (C1) the 2nd m (C2).). here -- 1 -- it should observe -- the 1st image and the 2nd image are becoming the image which was not symmetrical and turned to the same direction mutually to optic-axis (X). Therefore, by detecting each illumination distribution of the 1st image on an imaging surface (FR) and the 2nd image, and detecting the interval between pictures, such a focus detecting device is constituted so that the focal regulation state of a photographing lens may be detected. In such a focus detecting device, in order to make exact focal detection, 1st Image 2 image formed of an imaging lens (Ll) and (B-2), respectively must serve as II and < 1-time distribution which correspond to ' usual state mutually. However, when a condensing lens (LO) consists of spherical lenses like Le I figure illustration, Since a Distortion difference is generated and this Distortion difference affects it symmetrically to optic-axis (X) with the condensing lens (LO), the 1st image and the 2nd image are subject to the influence corresponding, respectively of a mutually different Distortion difference for every portion. therefore -- consequential -- the 1st image and the 2nd image -- mutual -- Irritated -- illumination distribution does not become and exact focal detection may not be made. If this is explained in more detail, as shown in the graph of Drawing 2 (a) now, three symmetrical black lines will be used as a photographic subject to the optic axis (this is hereafter called main optic axis) of a photographing lens, and it will be referred to as h with the interval between each line. The illumination distribution on the imaging surface when this photographic subject's image is formed on each imaging surface of an imaging lens (Ll) and (B-2) in response to the influence of the Distortion difference of a condensing lens (Lo) becomes as it is shown in Drawing 2 (b). In 2nd [ The ] figure ■ Application, a horizontal axis shows the position of a direction perpendicular to main optic-axis (X). In Drawing 2 (b), since a Distortion difference occurs symmetrically to main optic-axis (X), it is set to a4 =b 2. a 2=b l, and a+=b+ does not become. and since an imaging lens (Ll) and (B-2) are carrying out eccentricity to main optic-axis (X), 2 resembles the image interval on the optic axis of each lens (Ll) and (B-2), and + differs in 8. since 8 is symmetrical with K1 to an optic axis, even if it is carrying out eccentricity, it is alike, and is set to +=Ks. Therefore, + differs also from K2. ks at the interval between the images of a corresponding black line, respectively, and it becomes difficult to detect the interval of the 1st image and the 2nd image. Object The present invention is made in view of the point like Above, and the object is generating of the Distortion difference like Above. It is in offering. EXAMPLE hereinafter, a drawing -- Group -- it DETAILED DESCRIPTION OF THE INVENTION just. Drawing 3 is a figure showing the basic optical system of the focus detecting device in a present invention example, a same sign is account ° Carried out about the same thing as the conventional example of 1st [ The ] figure 1, and the explanation about them is omitted. This example achieves the above-mentioned object by introducing an aspheric surface into the front side lens surface (rz) of a condensing lens (Lo). the composition of the basic optical system before I will and aspheric surface introduction is shown in the 1st table. 1st Table Curvature-radius (r) axis top interval (d) JijJ box Tea room (Nd) schedule focal plane (1=') rl=■dI=411IIIO d s = 10.3 Relation 1.0 Magnification Beta-o, 32 This example makes a front side lens surface (r2) of a condensing lens (LO) a Rotating twins ' curved surface. Hail of the shape is carried out as follows. ° First, take X coordinates in the direction parallel to main optic-axis (X), and take X coordinates and two coordinates to a 2-way perpendicular to it. The starting point is made into the intersection of main optic-axis (X) and the above-mentioned lens surface (r2), and it is c. When being it Paraxial curvature radius 10.862111 of a With lens surface (r2), the rotation hyperbolic side of the lens surface (r2) is A'X2+y2+Z2. -- =0 -= music ....... Music .. Hail is carried out to concave (1) O, and it is E=-4. Here, with the value, E determines the shape of a lens surface (r2), and becomes a rotation hyperbolic side at a paraboloid of revolution and the time of E< 0 at ellipsoid of revolution and the time of E-0 at the time of a surface of a sphere and E>o at E == and the time of 1. In order to show the effect of this example, table-ization of the Distortion difference in the imaging surface (FR) of an imaging lens (Ll) when various E of (1) type is changed in the composition of the 1st table and a lens surface (r2) is made into the aspheric surface of various shape, and (L2) is shown in Drawing 4. It is E To so that clearly from Drawing 4. It is Drawing 2 (a) about the case of the surface of a sphere of E= 1, and the case of the rotation hyperbolic side of E =-4. The relation of 2 is shown in Drawing 5 at h of (b) illustration at +-. the direction of this example using the rotation hyperbolic side of E=-4 is alike compared with the case of the surface of a sphere of E and =l, table-izing of 2 is small, namely, 1- has little influence on the focal detecting accuracy of a Distortion difference so that clearly from Drawing 5. k2 shows the interval between the re-image formation images according a schedule focal plane (F) to a pair of imaging lenses (Ll) of the image of an intersection ball with main optic-axis (X), and (L2) here, and kI shows the interval between the re-image formation images of the image on the schedule focal plane (F) which separated only A distance from the above-mentioned intersection in the direction perpendicular to main optic-axis (X). In the composition of the 1st table of the above, it is good also considering the backside lens surface (rs) of a condensing lens (LO) as an aspheric surface. The relation between the shape of the aspheric surface in this case and a Distortion difference is shown in Drawing 6. Drawing 6 -- Tari and others -- as -- even if it introduces an aspheric surface into the backside lens surface (rs) of a condensing lens (Lo), in the case of the surface of a sphere of E= 1, a Distorted difference can be satisfactorily amended to a ratio, and it is especially the most effective when it is a rotation hyperbolic side of E=-1. However, E is E of (1) type and is Co=-9,064 in this example here. The 2 2nd table in which the 2nd table shows the optical system before the aspheric surface introduction in another example of the present invention Curvature-radius (6) axis top interval (d) refractive-index (Nd) schedule focal plane (1') r+ =o. d+=4u 1.□ d8 Wo lO, '31111.0 Magnification beta= 045 This example also introduces the rotation hyperbolic side used as E=-6 of (1) type into the front side lens surface (r2) of a condensing lens (LO). The rotation hyperbolic side which replaces with it and is set to E=-2 of (1) type at a backside lens surface (rs) may be introduced. When Drawing 7 shows change of the Distortion difference in the imaging surface of imaging lens (Ll) at the time of Ran away (L2) for various E of (1) type in order to show the effect of this example, and A makes an aspheric surface a front side lens surface (r2), B is carrying out hail of the case where a backside lens surface (rs) is made into non-Reason m1. It is E= like this example so that clearly [ Drawings 7 ]. - (when the rotation hyperbolic side of , is introduced into a front side lens surface (r2), or when the rotation hyperbolic side of E=-2 is introduced into a backside lens surface (rs), a Distortion difference can be amended best.) The present invention should just be 0, i.e., a rotation hyperbolic side, in what is limited to the above-mentioned example. various methods of expressing an aspheric surface are known by History -- y 2 [ for example, ] (1) type is developed as +Z 2-phi2 -- coming -- When -- . On the other hand, hail of the general formula of an aspheric surface is carried out to x=co'[1-(1-ECo2phi2) 2]+ and sigmaCiphi2'-(3)1=1. ci (i=1.2.3. ...) is a coefficient which defines the shape of an aspheric surface. Here, it becomes if the aspheric surface acquired by the slight modification from a standard surface of a sphere is shown at the time of E= 1 and it develops this. (2) It is C0=C0 when a formula is compared with (4) types. 1-O C2=-Co8(A/-1) C++=-Co5 (L"2-1) 8 It becomes having defined E and homonymy. Therefore, the present invention is not limited only to strict rotation hyperbolic jn1 like the above-mentioned (1) formula, It is divided by the main mirror (MM) and the light which showed the composition included in slight Transform from a rotation hyperbolic side, and penetrated the photographing lens (TL) in the figure is one side, A focal board (1 :P), pen Taprism (it is led to the Fake optical system which is based and has an eyepiece (CL), and another side is led to the focal detection module (FM) which penetrated the main mirror (MM), was reflected by the submirror (sNr), and is arranged behind Genus 1 equivalent to a film plane (J The).) The light which entered into the focal detection module (1 and "xi) is condensed with a condensing lens (LO), it is reflected by the mirror (M), and what penetrated the infrared cut filter (l F) receives both two images formed with an imaging lens (Ll), respectively. EFFECT OF THE INVENTION As mentioned above, the present invention arranges a condensing lens behind the schedule focal plane of a photographing lens, In a focus detecting device of a camera which performs focal detection of the above-mentioned photographing lens by comparing mutually an image of a schedule focal plane which arranges a pair of imaging lenses to optic-axis symmetry, and is formed with both Statue lens behind the condensing lens, respectively, At least one lens surface of the above-mentioned condensing lens was made into an aspheric surface. By constituting in this way, aggravation of focal detecting accuracy by a Distortion difference symmetrical with the main optic axis generated by condensing lens (Lo) can be prevented, and exact focal detection can be enabled. a rotation hyperbolic side is used like especially an embodiment -- having -- amendment of a Distortion difference becomes good.

[Brief Description of the Drawings]

The graph graph The WS 2 figure &lt;- for Drawing 1 to illustrate the fault for Ganseng honorable base of the conventional focus detecting device in 1000 Sectional view and Drawing (a) 2 ■ indicates the luminance distribution on a schedule focal plane to be, In Drawing 2 (b), 3rd [ The ] figure 1 is a graph which shows the illumination distribution on image formation ml of an imaging lens, and Disconnect mI figure which shows the optical system before aspheric surface introduction of present invention 1 example, The graph which shows the relation between E of (1) type, and a Distortion difference in order that Drawing 4 may show the effect, The graph Drawing 5 indicates change of the distance between images on the imaging surface of a conventional example and this example to be, The graph which shows the relation of E of (1) type and a Distortion difference, the graph which shows a relation with E 7 Distortion difference of (1) type in example with another Drawing 7, and Drawing 8 are sectional views showing the state where present invention Monk * was included in the one eye reflex camera. [ in / in Drawing 6 / the modification ] (rL) : 4t+3 a shadow lens, (F); schedule focal plane, (Lo); a condensing lens, (Ll) (L2); a pair of imaging lenses. Above Drawing 2 of applicant Minolta Camera Co., Ltd. (thetalambda) Drawing 4 (%) l-1-J-4-t I To Drawing 3 Zth [ The ] figure tb mb figure (%) Drawing 5 Drawing 7 2 T O -T -E-3-4-5-6