JPH0516568Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a focus detection device for a camera, and more particularly to a condenser lens used in a focus detection device for a camera and a mounting portion thereof.

Prior Art Two imaging optical systems are arranged behind the expected focal position of the taking lens, and the relative position of the image obtained by re-forming the image taken by the taking lens by the imaging optical system is detected, and the relative position of the image of the taking lens is detected. Focus detection devices have been proposed that are configured to detect focus conditions.

This focus detection device includes a condenser lens placed near a planned focal plane of a photographic lens, a mask plate placed behind the condenser lens, and two imaging lenses arranged approximately at each image forming plane. The line sensor detects the relative position of the two images re-formed by each imaging lens, and detects the focus adjustment state of the photographing lens.

In this type of focus detection method (phase difference focus detection method), the configuration of the device itself is an extremely important element in determining focus detection accuracy. However, few of the conventional focus detection devices of this type are constructed after sufficiently analyzing various factors of focus detection errors that occur in conjunction with the construction.

In particular, considerable power is required for the condenser lens that back-projects the aperture of the mask plate onto a predetermined pupil position of the photographic lens in order to accurately regulate the area through which the light beam incident on the line sensor passes through the photographic lens. be. For a condenser lens with such strong power, in order to sufficiently eliminate focus detection errors, aberrations (particularly distortion) must be well corrected and it must be positioned with extremely high precision relative to the line sensor. There is.

JP-A-58-106511 discloses a focus detection device in which a condenser lens, an imaging lens, and a line sensor are integrated as a module, but from the viewpoint of aberration correction and positioning accuracy of the condenser lens, As can be seen, it cannot be said that various factors contributing to focus detection errors have been sufficiently eliminated.

Purpose In view of the above-mentioned circumstances, the present invention provides a focus detection device that sufficiently eliminates focus detection errors caused by its configuration.
In particular, it is an object of the present invention to provide a focus detection device in which aberration correction and positioning accuracy in a condenser lens have been sufficiently studied.

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 shows the arrangement of the optical system, etc. when the focus detection device according to the present invention is applied to a single-lens reflex camera. In FIG. 1, a photographing lens TL, a movable mirror 2, a focusing plate 4, a pentaprism 6, etc. are well-known elements constituting a single-lens reflex camera. However, if the camera is configured to perform automatic focus adjustment using the output of the focus detection device, the focus adjustment optical system of the photographing lens TL is driven by a lens drive device including a motor (not shown). It is configured as follows.

The center part of the movable mirror 2 is formed to be semi-transparent, and a sub mirror 8 is provided behind it. is guided to a focus detection device 10 located below.

The focus detection device 10 includes a visual field mask member 12, a condenser lens LC, a reflector 14, a mask plate 16,
It is equipped with imaging lenses L1 and L2 and a line sensor 18, and the output of the line sensor 18 is processed by a signal processing circuit (not shown) to generate a defocus signal indicating the amount and direction of focus deviation from the in-focus position. Ru. Based on this defocus signal, the focus adjustment state is displayed on a display device (not shown), and the focus adjustment lens of the photographing lens TL is driven to the in-focus position by a drive device (not shown).

FIG. 2 is a diagram showing the basic optical system of the focus detection device, where the dashed line Z indicates the optical axis of the photographing lens TL.
A dotted line F indicates the expected focal position of the photographing lens TL (a position equivalent to the film exposure surface). The condenser lens LC is slightly (for example, 4
mm) is placed in the rear position. Imaging lenses L1 and L2 are arranged behind the condenser lens LC with the optical axis Z as an axis of symmetry, and a mask plate 16 having openings A1 and A2 is provided in front of these imaging lenses L1 and L2. ing. A line sensor 18 made of a CCD is arranged on the imaging plane of each imaging lens L1, L2.

The condenser lens LC has the power to form images of the apertures A1 and A2 of the mask plate 18 at the pupil position of the photographing lens TL, and
The size of is set so that only the object light that passes through an aperture corresponding to a specific aperture value, for example, F5.6, out of the object light that passes through the photographic lens. As a result, even if various photographic lenses are used, if the photographic lens has an open aperture value smaller than F5.6, the subject image received by the line sensor 18 will not be offset by the aperture of the photographic lens TL. There is no.

Images If, Io, and Ib on the optical axis represent images in the front focus, in-focus, and back focus states, respectively, with respect to the subject in front of the photographic lens TL. The re-imaged images of these images If, Io and Ib by the imaging lenses L1 and L2 are I1f, I1o and I1, respectively.
b, and I2f, I2o, I2b.
That is, the re-imaging images I1o, I2o of the focused image Io
is connected to a position slightly in front of the line sensor 18, and the re-imaged images I1f and I2f of the front-focus image If are
The re-imaged images I1b, I2b of the rear-focused image Ib, which are focused in front of the focused re-imaged images I1o, I2o and closer to the optical axis Z, are the focused re-imaged images I1
o, I2o and at a position away from the optical axis Z. Here, the position of the image formed by the photographing lens TL is opposite to the distance between the two re-imaged images,
The line sensor 18 determines rear focus and front focus depending on whether the distance between the two re-imaged images is longer or shorter than the distance between the two re-imaged images at the time of focus, and the distance between the two re-imaged images is determined by The amount of defocus is then detected. In other words, the line sensor 18 has a large number of pixels arranged along the moving direction of the re-imaged image, and detects how many pixels apart the pattern of the re-imaged image is repeated. Detect the distance of the re-imaged image.

3 to 6 show an enlarged view of the focus detection device 10 configured as one module.

In the figure, the condenser lens LC is composed of a plastic lens, and has an aspherical convex lens surface 20 on the upper surface and a spherical convex lens surface 22 on the lower surface, and the condenser lens LC is perpendicular to the optical axis direction arranged around the aspherical convex lens surface 20 and the lower surface. It is constituted by a plastic lens formed from a flange surface 24 and a side circumferential surface 26 perpendicular to the flange surface 24. The condenser lens attachment part 32 formed on the upper wall of the support body 30 has a circular aperture 34 forming an optical path, and an optical axis formed so as to be orthogonal to the optical axis direction around the aperture 34 and in contact with the collar surface 24. It includes a direction positioning surface 36 and an optical axis positioning surface 38 formed to be perpendicular to the positioning surface 36 and to fit into the side peripheral surface 26 . For this reason, the condenser lens LC is attached to the lens mounting part 3.
2, the flange surface 2 of the condenser lens LC
4 and the side circumferential surface 26 contact and fit into the positioning surfaces 34 and 36 of the lens mounting portion 32, respectively, so that the position of the condenser lens LC in the optical axis direction and the alignment of the optical axis with respect to the support body 30 are achieved with high precision. And it's easy to do.

The visual field mask member 12 has a circular recess 12 on the lower surface.
a, and an upper wall 12c made of a light-shielding material that has a long rectangular opening AS in the direction parallel to the arrangement direction of the line sensor 18 at the center of the circular recess 12a and is large enough to cover the entire condenser lens LC; It includes two legs 12d and 12e extending downward from the lower surface of the upper wall 12c. Legs 12d, 1
Hook portions 12h and 12i are formed at each tip of 2e and have contact surfaces 12f and 12g that are inclined with respect to the horizontal plane. This field mask member 12 is inserted into the rectangular mounting hole 31a of the upper wall 31 of the support while elastically deforming the legs 12d and 12e outward, while the leg 12e is inserted into the rectangular mounting hole 31a of the upper wall 31 of the support. By bringing the hooks 12h and 12i into contact with the side surface 31b of the wall 31, the lower corner portion 31 of the support upper wall 31
c, 31d and attached to the support body 30. In the installed state, the inclined contact surface 1
2f and 12g come into elastic contact with the lower corners 31c and 31d of the support upper wall 31 due to the elastic force of the legs 12d and 12e to restore themselves inwardly, and as a result, the upper wall 12c of the visual field mask member 12 elastically moves downward. A pulling force is generated, and the chamfer 12j around the circular recess 12a of the upper wall 12c presses the condenser lens LC from above. This makes the condenser lens LC
is integrally fixed to the support body 30. The longitudinal position of the rectangular opening AS of the field mask plate 12 is 12o,
12p, 12q, and 12r are the inner wall surface 3 orthogonal to the longitudinal direction of the rectangular mounting hole 31a of the support upper wall 31.
1k and 31l, and the inner wall surfaces 31m and 31m perpendicular to the side surface 31b, respectively.

The upper wall 12c of the field mask member 12 restricts the incident light to the condenser lens LC to only the light incident from the rectangular aperture AS to prevent the incidence of harmful stray light, and also prevents the incidence of harmful stray light. be regulated within a predetermined range.

The reflecting mirror 14 is fixed to the support body 30 in an attitude inclined at 45 degrees with respect to the horizontal plane, and guides the light from the condenser lens LC toward the line sensor 18.
The infrared cut filter 40 is fixed to the support 30 in a vertical position at a position facing the reflecting mirror 14, and blocks infrared light harmful to focus detection.

The mask plate 16 is made of a light-shielding material and has two approximately elliptical openings A1 and A2 formed in the center.
and mounting holes 16a, 16b formed at the ends, and the mounting holes 16a, 16b are fitted into the pins 30a, 30b of the support body 30, and the openings A1 and A
2 is fixed at a position overlapping the circular opening 30c of the support 30, and as mentioned above, the photographing lens
Only light from a predetermined aperture at the pupil position of the TL is transmitted. The imaging lens member 42 is made of a transparent material, and includes imaging lenses L1 and L2 formed in the center so that parts of the imaging lenses L1 and L2 intersect with each other, and has mounting holes 42a and 42b for mounting. The holes 42a and 42b are fitted into the pins 30a and 30b of the support body 30, and the mask plate 16 is fixed to the support body 30 while being overlapped with the mask plate 16. Thereby, the imaging lenses L1 and L2 are connected to the mask plate 16.
facing openings A1 and A2, respectively.

The sensor unit 44 includes a line sensor 18 made of a CCD that is directly die-bonded to a base plate 48, and a lead portion 46 that is connected to an external board.
and a protective glass 52 fixed in front of the line sensor 18 via a spacer 50, and the line sensor 18 is sealed by the base plate 48, the spacer 50, and the protective glass 52. The sensor unit 44 is fixed to the support 30 with the base plate 48 in contact with the front end surface 30d of the support 30.

In this way, the focus adjustment device 10 includes the field mask member 12, the condenser lens LC, the reflector 14, the mask plate 16, and the imaging lenses L1 and L.
2 and the line sensor 18 are positioned at predetermined positions with respect to the support 30 and are integrally coupled. The support body 30 has mounting holes 31e, 31f, and 31g formed in its upper wall 31.
It is fixed to the bottom wall 54 of the mirror box.

FIGS. 7 and 8 show an embodiment in which a second flange surface and a side peripheral surface are further added to the upper surface of the condenser lens. That is, the condenser lens LC is similar to the embodiments shown in FIGS. 3 to 6.
The support body 30 is provided with a flange surface 24 and a side peripheral surface 26 that abut or fit on the optical axis direction positioning surface 36 and the optical axis positioning surface 38 of the lens attachment part 32, and around the convex lens 20 on the upper surface. It includes a second flange surface 25 that is orthogonal to the axial direction and a second side peripheral surface 27 that is orthogonal to the second flange surface 25 .

On the other hand, the field mask member 12 is shown in FIGS.
A light shielding part 12b rectangular opening AS similar to the embodiment shown in the figure,
The inner circumferential wall 12k of the circular recess 12a is provided with leg portions 12d, 12e and hook portions 12h, 12i.
is formed so that it fits into the side circumferential surface 27 of the condenser lens LC, and the lower surface 12l of the upper wall 12 abuts against the flange surface 25. With this, the visual field mask member 12 can move the condenser lens LC to the support 3.
0, and lower surface 12l and inner peripheral wall 1.
2k contacts or fits into the flange surface 25 and side peripheral surface 27 of the condenser lens LC to form a rectangular aperture AS.
is precisely positioned with respect to the condenser lens LC.

Note that the condenser lens LC may have both surfaces formed as aspherical convex lens surfaces or both surfaces as spherical convex lens surfaces.By configuring both surfaces as convex lens surfaces, sufficient power can be obtained and aberrations can be reduced. . Note that by configuring at least one surface as an aspheric lens, distortion of the re-imaged image on the line sensor 18 can be reduced.
In this way, when an aspherical lens surface is formed on a condenser lens, particularly strict optical axis alignment is required, but by using the present invention, the optical axis alignment can be easily performed.

Effects The focus detection device of the present invention includes two re-imaging lenses that re-form the image formed by the photographing lens;
Detects the relative position of a plastic condenser lens placed in front of the re-imaging lens and constructed separately from the re-imaging lens, and the two images re-formed by the re-imaging lens. The condenser lens has a support body coupled to form an integral module, and the condenser lens includes a lens portion having an aspherical surface, and a lens portion surrounding the lens portion. A flange surface arranged between both lens surfaces and formed to be substantially orthogonal to the optical axis direction; A lens mounting portion that supports the condenser lens on the support body is integrally formed with a side circumferential surface formed to It is equipped with an axial positioning surface and an optical axis positioning surface that is perpendicular to the optical axis direction positioning surface and is formed to fit into the side circumferential surface, and by the abutment and fitting of each of the above surfaces. The position of the condenser lens on the optical axis and the position perpendicular to the optical axis are regulated.

Therefore, the aspheric surface formed on the condenser lens improves distortion, which is a problem when re-imaging an image on the line sensor. Furthermore, when an aspherical surface is formed on the condenser lens, it is necessary to position the condenser lens with respect to the line sensor with sufficient accuracy, but in the present invention, the condenser lens and the line sensor are integrally configured as a module, and Since the condenser lens is supported by the lens mounting portion between the lens surfaces, it is easy to achieve high precision, and it is also possible to sufficiently absorb deformation due to water absorption and temperature changes, which are problems with plastic lenses.

[Brief explanation of drawings]

Figures 1 to 6 show an embodiment of the present invention, in which Figure 1 is a side sectional view of a single-lens reflex camera, Figure 2 is a layout of the basic optical system, and Figure 3 is a focus FIG. 4 is a plan view, FIG. 5 is a side sectional view, and FIG. 6 is an exploded perspective view of the detection device as seen from below. 7 and 8 show modified embodiments, with FIG. 7 being an exploded perspective view and FIG. 8 being a side sectional view. LC... Condenser lens, 24... Tsuba surface, 2
6...Side peripheral surface, 32...Lens mounting portion, 36...
Optical axis direction positioning surface, 38...Optical axis positioning surface.

Claims (1)

[Claims for Utility Model Registration] Re-forming an image formed by a photographic lens 2
a plastic condenser lens placed in front of the re-imaging lens and configured separately from the re-imaging lens; and two re-imaging lenses that are re-imaged by the re-imaging lens. A line sensor for detecting the relative positions of the two images has a support combined to form an integrated module, and the condenser lens includes a lens portion having an aspherical surface and a periphery of the lens portion. A flange surface that is large and is arranged between both lens surfaces constituting the lens portion and is formed to be substantially orthogonal to the optical axis direction; and a side circumferential surface formed to be substantially orthogonal to the flange surface, and a lens mounting portion for supporting the condenser lens on the support body is provided with a side circumferential surface that is substantially orthogonal to the optical axis direction and formed to be substantially perpendicular to the flange surface. The optical axis positioning surface is formed to be in contact with the optical axis direction positioning surface, and the optical axis positioning surface is perpendicular to the optical axis direction positioning surface and formed to fit in the side circumferential surface. A focus detection device for a camera, characterized in that the position of the condenser lens on the optical axis and the position in a direction orthogonal to the optical axis are regulated by contacting and fitting.