JPS629882B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a focus position detection device that is effective for focusing, for example, a camera.

Various detection devices of this type have been proposed in the past, but none have yet been fully satisfactory. For example, an autofocus lens is known in which a refractive optical element such as a polysm is placed on the imaging plane and is oscillated or rotated to detect the conversion of the light receiving element output to direct current during focusing. . However, in such a device that moves the refractive optical element, a mechanism for driving the refractive optical element must be interposed between the autofocus lens and the light receiving element, and for this reason, this mechanism is difficult to use. This method requires a large amount of space, and has the disadvantage that the camera configuration is complicated and large.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a focus position detection device that can accurately perform autofocus with a fixed refractive optical element.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A case where a focal position detection device according to an embodiment of the present invention is installed in a camera will be described below with reference to the accompanying drawings.

Reference numeral 1 in FIG. 1 indicates a lens frame provided on the camera body 2 so as to be rotatable about the central axis l and movable in the direction of the arrow along the central axis l. This lens frame 1 has an autofocus lens 3 arranged so that its optical axis m is parallel to the central axis l.
That is, it is attached and held eccentrically. Thus, when this lens frame 1 is rotated by the first motor 4, the lens 3 is revolved around the central axis l. Furthermore, when the lens frame 1 is moved in the direction of the arrow with respect to the camera body 2 by the second motor 5, the lens 3 is also moved in the same way. The lens 3
Behind the lens frame 1, a refractive optical element 6, a re-imaging lens 7, and a light receiving element array 8 are sequentially arranged coaxially with the lens frame 1. The refractive optical element 6 includes a plurality of triangular pyramidal prisms, for example, eight prisms arranged along the central axis l.
They are arranged radially around the center and are fixed to the camera body. On the other hand, the light receiving element array 8 is rotatably provided in the camera body about the central axis l, and the refractive optical element 6
Eight light receiving elements are arranged radially so as to optically face the prism. The lens frame 1 is provided with a synchronizing signal so that when the optical axis m of the lens 3 comes to the center of each light receiving element of the light receiving element array 8 as the lens frame 1 rotates, the output of this light receiving element can be taken out. A generator 9 is provided. A known pulse generator may be used as the synchronization signal generator 9, and for example, a plurality of contacts are arranged at equal intervals on the lens frame 1, and these contacts are sequentially scanned as the lens frame 1 rotates. and a slider.

The operation of the focus position detection device having the above configuration will be explained below together with its detection circuit.

Both motors 4 and 5 are driven to rotate the lens frame 1 and move it in the focusing direction. At this time, based on the output of the synchronizing signal generator 9, the output of the light receiving element through which the optical axis m passes is selected from among the outputs of the light receiving element array 8 by the output signal selection circuit 10 and sequentially scanned. Since this scanning signal is discontinuous, it is converted into a continuous signal by the D/A converter 11 at the next stage, and an output signal as shown in FIG. 2a is obtained. In this figure, in the defocus state, the image on the light receiving element array 8 also changes sequentially by each prism of the refractive optical element 6, so the output signal from the light receiving element array 8 becomes an AC signal, but in the focusing state, the image on the light receiving element array 8 changes sequentially. It becomes a DC signal as shown in the vicinity indicated by P. Therefore, it is sufficient to detect this DC signal, and for this purpose, the D/A converter 1
A DC cut filter 12 is connected to the output side of 1, which removes unnecessary DC components other than the scanning AC signal. Then, the output signal from now on is amplified by the amplifier 13, and the focus position detection circuit 1
The focal position is detected at 4, and the control circuit 15 controls the driving of both the motors 4 and 5. A low-pass filter 16 is also connected to the output side of the D/A converter 11, and an output signal as shown in FIG. 2b is obtained in the vicinity of focusing. This output signal is amplified by an amplifier 17, waveform-shaped by a waveform shaping circuit 18, and then by a differentiating circuit 19.
The output signal shown in c of FIG. 2 is obtained. This output signal is sent to the next stage front and rear focus detection circuit 20.
The positive and negative values are detected, and thereby it is recognized whether the focus is on the front or the back, and the output signal from this is sent to the control circuit 15 to control the motors 4 and 5. .

In the apparatus of the above embodiment, by reducing the eccentricity of the optical axis of the autofocus lens with respect to the central axis of the lens frame, the autofocus lens can also be used as a photographing lens of a camera. On the other hand, if the lens is not used in combination, the movement of the autofocus lens and the movement of the photographic lens may be synchronized. Further, in the embodiment, the autofocus lens is moved back and forth by the second motor, but it may also be moved manually, for example, by rotation, as in the case of a photographic lens of a camera. The number of prisms of the refractive optical element and the number of light receiving elements of the light receiving element array do not necessarily have to match, and from the viewpoint of accuracy, it is preferable that the number of these is as large as possible. Note that the re-imaging lens is added to increase the effect and is not necessarily necessary.

As explained above, the focus position detection device according to the present invention rotates the autofocus lens eccentrically through the lens frame, and receives light through the refractive optical element on the optical axis that changes due to the rotation of the lens. Since the element array scans sequentially, there is no need to provide any mechanism to drive the refractive optical element between the autofocus lens and the light receiving element, and this makes it possible to use this in cameras. When doing so, it is possible to prevent the configuration from becoming more complicated and larger.

[Brief explanation of the drawing]

The drawings are for explaining a focal position detection device according to an embodiment of the present invention, and FIG. 1 is a diagram showing the position and its detection circuit, and FIG. 2 is a diagram showing a predetermined stage in the detection circuit. FIG. 3 is a diagram showing an output waveform at 1... Lens frame, 2... Camera body, 3... Auto focus lens, 4... First motor,
5... Second motor, 6... Refractive optical element, 8
...Photodetector array.

Claims (1)

[Claims] 1. An autofocus lens, and a lens that holds the autofocus lens with its optical axis decentered and is movable along the optical axis and rotatable about its own central axis. a frame; a refractive optical element provided on the imaging plane of the autofocus lens and having a plurality of refractive optical parts arranged radially around the central axis of the lens frame; and a refractive optical element that receives transmitted light from the refractive optical element. a light-receiving element array consisting of a plurality of light-receiving elements arranged radially so as to optically correspond to the plurality of refractive optical parts; and a synchronization signal that generates a synchronization signal as the autofocus lens rotates. a signal selection circuit that receives this synchronization signal and selects and sequentially scans the outputs of the light receiving elements passing through the optical axis of the autofocus lens from among the outputs of the light receiving element array; A focus position detection device comprising: a detection circuit that detects a focus position from an output of a selection circuit.