JPH0364845B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a relay adapter that relays between an interchangeable lens and a camera body, and particularly to a teleconverter that enables automatic focus adjustment of an interchangeable lens.

2. Description of the Related Art Conventionally, a teleconverter is known which is equipped with an automatic focus adjustment device including a focus detection device within an adapter body of an adapter that relays between an interchangeable lens and a camera body. This teleconverter consists of a conversion optical system inside the adapter body consisting of a negative front group lens and a positive rear group lens, and a reflecting mirror is installed in the light beam between the front group lens and the rear group lens. A portion of the light beam diverted by the reflector is guided to a light receiving element of a focus detection device, and the focus of the interchangeable lens is adjusted by moving only the front lens group back and forth in accordance with the output of the focus detection device. ing. This teleconverter has the effect of enabling automatic focus adjustment using an interchangeable lens and a camera body that does not have any means for automatic focus adjustment, but some of the light that has passed through the interchangeable lens
Since the light is cut by a reflector installed between the moving negative front group lens and the fixed positive rear group lens, the amount of light reaching the film surface is reduced, resulting in underexposure during shooting. Or, with a single-lens reflex camera, the viewfinder may become dark, making it difficult to observe. Furthermore, since the reflecting mirror is disposed in front of the rear group lens, it is necessary to increase the distance between the front group lens and the rear group lens. For this reason, not only does the length of the adapter main body in the optical axis direction become longer, but also the aperture of the rear group lens must be increased, which has the disadvantage that the adapter itself becomes larger.

The present invention solves the above-mentioned drawbacks of the prior art and provides a teleconverter with a compact configuration that enables automatic focus adjustment using ordinary interchangeable lenses conventionally used in interchangeable lens cameras having an automatic focus detection function. The purpose is to provide

Hereinafter, the present invention will be explained in detail based on embodiments shown in the accompanying drawings.

FIG. 1 is a developed view of the camera as seen from above, with the optical system of a focus detection device provided on the side of the camera body to which the teleconverter of the present invention is mounted, and a photographing lens directly connected. In FIG. 1, two areas 1a and 1 of the exit pupil of the photographic lens 1 are symmetrical with respect to the optical axis.
A pair of imaging lenses 3
The light is received by the light receiving elements 4a and 4b by the light receiving elements 4a and 3b, and by comparing the deviation of the images on the light receiving elements 4a and 4b, the focus adjustment for the surface 5 where the focus should be matched (the surface conjugate with the film surface) is determined. This focus detection optical system is configured to be able to detect the state.
A camera equipped with such a focus detection device is already known, for example, from Japanese Patent Application Laid-open No. 147430/1983.

In the focus detection optical system shown in Fig. 1, the angle θo corresponding to the open F-number Fo of the photographic lens 1 and the angle to the outermost ray of the light flux for detection (indicated by hatching) (hereinafter simply referred to as "maximum (hereinafter referred to as the "acceptance angle"), there must be the following relationship to prevent detection from being inaccurate due to vignetting of the detection light.

θo≧ ...(1) In this formula (1), if Fd is the F value for focus detection corresponding to the maximum acceptance angle, that is, the largest F value that allows focus detection, then formula (1) is as follows. can be rewritten as .

Fo≦Fd...(2) The teleconverter installed between the photographic lens 1 and the camera body must also satisfy the above-mentioned condition for vignetting in equation (2).

On the other hand, in FIG. 2 for explaining the principle of the teleconverter in the present invention, the photographic lens 1
Assuming that the beam 6 from infinity is focused on a point A behind it, the distance fo from the rear principal point of the photographic lens 1 to the point A is equal to the focal length of the photographic lens 1. Assuming that the light beam 6 passes through the aperture D of the photographic lens 1, the F of this photographic lens is
The value is expressed as Fo=fo/D, and the angle θo corresponds to the open F value Fo of the photographing lens 1.

Assuming that a convergence lens 7 is provided behind the photographic lens 1 and that the light beam 6 converges and forms an image at point B, the combined focal length fc of the photographic lens 1 and the convergence lens 7 is as follows. This becomes larger than the focal length fo of the photographic lens 1. Also B
The angle θ between the luminous flux and the optical axis at the point becomes small, and θ<θo. Since Fc=fc/D, where Fc is the F value for this composite focal length, and fc>fo, fc/D>fo/D, that is, Fc>Fo.

Now, assuming that the magnification of the conversion lens is k, there is the following relationship between the F value and focal length of a single photographic lens and a combination of a conversion lens and a photographic lens.

fc=k·fo...(3) Fc=k·Fo...(4) That is, both the F number and the focal length become larger by the magnification of the conversion lens. In general, the larger the magnification k is, the more the distance from the rear end of the conversion lens to the focal point, the so-called back focus fB of the lens, can be made larger than the back focus of the photographic lens itself.

Now, the image of point B in FIG. 2 is transferred to the light-receiving element 4a,
In order to re-image the image on the 4b plane, this optical system must satisfy the above-mentioned equations (2) and (4) at the same time. That is, Fo≦Fd...(2) Fc=k・Fo...(4) In equations (1) and (2), if Fc=Fd, k≦Fd/Fo...(5) is obtained, and the convergence The magnification of the lens must be set to satisfy equation (5). Note that this convergence lens may consist of a plurality of lens groups, some of which may be moved during focus adjustment.

FIG. 3 shows an embodiment of the present invention.
Components that are the same as those in the figure are given the same reference numerals. At the rear end of the adapter body 10, which has a lens mount part 9 to which an interchangeable lens barrel 8 having an existing photographic lens 1 is removably attached, there is an adapter attachment part that can be detachably attached to the lens mount 11 of the camera body C. 12 is provided, and the adapter body 1
A conversion optical system 7 is provided within a movable lens barrel 13 that is screwed into the lens. A part of the light beam 6 that has passed through the photographic lens 1 and the conversion optical system 7 passes through the semi-transparent part 14a of the swinging mirror 14, is reflected by the sub mirror 15, and is reflected by a pair of light beams as shown in the first figure. The light enters the light receiving elements 4a, 4b via the imaging lenses 3a, 3b. Note that the light beam reflected by the sub mirror 15 forms an image at a point B that is conjugate with the film surface F. On the other hand, the light beam reflected by the swinging mirror 14 forms an image on the focusing plate 16, and this image is formed by a condenser lens 17, a pentaprism (not shown), and a viewfinder eyepiece 18.
observed through. The outputs of the light receiving elements 4a and 4b are sent to the next focus detection circuit 19, and the focus adjustment state is determined. This discrimination signal is sent to a drive circuit 20 within the adapter body 10, and the rotation of the reversible motor 21 is controlled by this drive circuit 20. Furthermore, the rotation of the reversible motor 21 is transmitted to the movable lens barrel 13 which has a gear 23 with wide teeth that meshes with the drive gear 22. Moving lens tube 1
3 rotates, the movable lens barrel 13 rotates and moves in the optical axis direction by the helicoid screw 24, so that the conversion optical system 7 provided inside
Focus adjustment is performed by moving along the optical axis while also rotating. Focus adjustment is completed, and the pair of photoelectric elements 4a
When the outputs 4b and 4b become equal, the focus detection circuit 19 detects this, stops the motor 21, and also stops the conversion optical system 7.

Since the embodiment of the present invention is configured as described above, in order for the convergence lens 7 to move from the in-focus position for a subject at infinity to a subject at a short distance, the convergence lens 7 must be replaced. It must move in the opposite direction to the lens, i.e. to the left and right in the figure. This amount of movement increases as the subject gets closer and as the focal length of the photographic lens 1 becomes longer. Therefore, in order to reduce this amount of movement, it is sufficient to reduce the focal length of the conversion lens 7 itself, that is, to increase the magnification k. However, as described in the explanation for FIG. 1, this conversion lens 7 must be constructed so as to satisfy the eclipse condition, that is, the equation (5) of k≦Fd/Fo. Although the conversion lens 7 is formed as a biconcave lens in the figure, it may be any lens group that has negative properties, and in order to improve various aberrations, it may be a plurality of lenses that combine positive and negative lenses. It is actually composed of groups. Of course, when adjusting the focus, the whole part may be moved, or only a part thereof may be moved depending on the convenience.

In this embodiment, as a drive device, a drive circuit 20 and a reversible motor 2 are provided inside the teleconverter.
1. Although an example is shown in which a drive gear 22 is provided, it does not necessarily have to be in this form.

As described above, according to the present invention, when the camera side has an automatic focus detection function but the interchangeable lens side does not have an automatic focus adjustment function, the present invention not only enables automatic focus adjustment but also is compact and compact. You can get a rear converter with good operability.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram of the focus detection optical system on the camera body side used in the present invention, Fig. 2 is an explanatory diagram of the optical system of the teleconverter of the present invention, and Fig. 3 is an explanatory diagram of the optical system of the teleconverter of the present invention. FIG. 1 is a sectional view showing an embodiment of the invention. 1... Shooting lens, 7... Conversion optical system, 10... Adapter body, 12... Lens mount, {3a, 3b... Imaging lens, 4a, 4
b... Light receiving element, 19... Focus detection circuit} Focus detection device, {20... Drive circuit, 21... Reversible motor, 22... Drive gear} Drive device.

Claims (1)

[Scope of Claims] 1. A focus detection device that is installed on a lens mount and that is provided on a camera body and has a focus detection device that receives light beams from two areas of an exit pupil that are substantially symmetrical with respect to the optical axis of a photographic lens that is attached to the camera body, and that is attached to a lens mount. and the photographing lens, the teleconversion optical system having a negative refractive power and multiplying the focal length of the photographing lens by a predetermined magnification; a driving device that moves at least a part of the optical system in the optical axis direction and performs a focusing operation, and sets the F value determined by the maximum light receiving angle of the focus detection device to Fd, and sets the F value determined by the maximum light receiving angle of the focus detection device to the A teleconverter capable of automatic focus adjustment, characterized in that the conversion optical system is configured such that the predetermined magnification k satisfies k≦Fd/Fo, where Fo is the open F-number of the photographing lens.