JPH055526Y2 - - Google Patents

Description

[Detailed Description of the Invention] This invention relates to a control information retrieval device applicable to a focusing device of a zoom lens.

2. Description of the Related Art Conventionally, a focusing device has been known for a zoom lens that detects an image plane displacement amount (amount of deviation from the in-focus position of a focusing lens) and controls a helicoid for driving a first group focusing lens of the zoom lens.

By the way, it is known that the amount of image plane displacement for a fixed focusing lens drive amount is larger when the focal length is long (tele side) than when the focal length is short (wide side). Therefore, the first
The amount of drive of the helicoid to drive the group focusing lens is not determined only by the amount of image plane displacement;
It is a function of the amount of image plane displacement and focal length.

Conversely, when the focal length is relatively long, even if the first group focusing lens is driven slightly, the amount of movement of the image plane will change significantly compared to when the focal length is relatively short. When the focal length is relatively short, even if the first group focusing lens is moved significantly, the amount of movement of the image plane changes only slightly compared to when the focal length is relatively long. In other words, even if the amount of image plane displacement is constant, if the focal length is long, the helicoid drive amount must be relatively small, and if the focal length is short, the helicoid drive amount must be relatively large. No.

Therefore, the conventional focusing device includes a focal length detection device for detecting the focal length of the zoom lens;
A pulse encoder for controlling the amount of drive of the focus motor is separately provided, and the focus motor is driven according to the focal length and image plane displacement amount of the zoom lens to perform automatic focusing.

However, in conventional focusing devices, the focal length detection device has a complicated mechanism and is provided separately from the pulse encoder. There was a problem that the focusing device occupied a large proportion of space.

This invention was made in view of the problems of the above-mentioned prior art, and its purpose is to:
An object of the present invention is to provide a zoom lens control information retrieval device that makes it unnecessary to provide a dedicated focal length detection device mechanism when used in an automatic focusing device.

In order to achieve the above object, the zoom lens control information retrieval device according to this invention includes a light emitting element and a light receiving element that are provided facing each other and whose relative distance changes in response to changes in the focal length of the zoom lens. and a slit plate that is driven by a focus motor that drives the focusing lens in the zoom lens and that intermittently blocks the optical path between the light emitting element and the light receiving element; The present invention is characterized in that it includes a pulsing circuit that divides an output signal from a light-receiving element, which changes sinusoidally and whose amplitude changes with a change in relative distance, at a plurality of threshold levels and outputs pulses.

According to this invention, the relative distance between the light emitting and light receiving elements changes in response to changes in the focal length of the zoom lens, so the control information for the light receiving element includes the focal length of the zoom lens, and the pulse The conversion circuit outputs pulses related to changing the focal length and driving the focus motor.

An embodiment of the zoom lens control information retrieval device according to the invention will be described below with reference to the drawings.

In FIG. 1, reference numeral 1 denotes a zoom ring for changing magnification that can be rotated around an optical axis 0. Zoom ring 1
A cam groove 1a is formed in the zoom ring 1. A light emitting element 2 is provided on the outside of the zoom ring 1.
The zoom ring 1 can reciprocate in the direction of the optical axis 0 by the cam action with the cam groove 1a. It is to be noted that the zoom ring 1 may be one that reciprocates linearly in the direction of the optical axis.

A light receiving element 3 is provided opposite to the light emitting element 2. Between the light emitting element 2 and the light receiving element 3,
A slit plate 5 is provided that intermittently blocks the light beam from the light emitting element 2 toward the light receiving element 3.
This slit disk 5 is rotationally driven by a focus motor 4. This focus motor 4 is connected to a focus ring 7 via a gear 6 and an intermediate gear 6a.
Rotate around optical axis 0. Note that power is supplied to the light emitting element 2, focus motor 4, etc. from a power source (not shown).

When the slit disk 5 rotates continuously, the light receiving element 3 outputs a signal waveform as control information as shown in FIG. 3a. The amplitude of the output of the light receiving element 3 is large when the distance between the light emitting element 2 and the light receiving element 3 is small, and small when the distance is large. The output of the light receiving element 3 is input to a threshold level setting circuit 8 shown in FIG. The threshold level setting circuit 8 has a function of setting several threshold levels (see FIGS. 4 and 5) and slicing the output of the light receiving element 3 at each threshold level. A pulse generation circuit 9 is provided after the threshold level setting circuit 8. The pulse generating circuit 9 has a function of generating pulses based on each threshold level in response to the output of the light receiving element 3 as shown in FIG. 3b. That is, the pulse generation circuit 9 has a function of generating one pulse when the threshold level crosses the signal waveform, and the threshold level setting circuit 8 and the pulse generation circuit 9 process the control information into pulses. This constitutes a pulsing circuit that outputs pulses related to changes in focal length and driving of the focus motor 4.

The threshold level is set so that the number of pulses for a constant amount of image plane displacement remains constant regardless of changes in focal length.

The pulse output of this pulse generating circuit 9 is inputted to one input terminal of a comparator circuit 10. The output of the image plane displacement amount information circuit 11 is input to the other input terminal of the comparison circuit 10. Image plane displacement amount information circuit 11
has a function of outputting to the comparison circuit 10 image plane displacement amount information as the amount of deviation from the in-focus position (focus plane) detected based on a known detection means. Based on the image plane displacement amount information and the pulse output of the pulse circuit 9, the comparison circuit 10 operates the motor drive circuit 12 for driving the focus motor until the focusing lens is positioned at the in-focus position. Note that, as is conventional, the drive direction of the focus motor 4 is reversed or reversed depending on the positive or negative value of the image plane displacement amount information.

Next, the operation when the zoom lens control information retrieval device according to this invention is applied to an automatic focusing device for a zoom lens will be explained.

When the image plane displacement amount information is input from the image plane displacement amount information circuit 11 to the comparison circuit 10, the comparison circuit 10 drives the focus motor 4 via the motor drive circuit 12 to bring the focusing lens into focus. move towards. At this time, a sinusoidally changing signal is sent from the light receiving element 3 to the threshold level setting circuit 8.
is input. The amplitude of the output signal of the light receiving element 3 is
The amplitude of the output signal includes focal length information because it changes according to the increase or decrease in the relative distance between the light emitting element 2 and the light receiving element 3, and this relative distance increases or decreases according to the increase or decrease in the focal length of the zoom lens. It happens.

When the focal length is short, as shown in FIG. dense).
Furthermore, when the focal length is long, the number of pulses generated during one cycle of change is relatively small (the intervals between the generated pulses are coarse), as shown in FIG.

The comparison circuit 10 compares the pulsed image plane displacement amount information and the number of pulses input from the pulse generation circuit, and when they become equal, controls the motor drive circuit 12 to stop the focus motor 4. let

The threshold level is set so as to cancel out the change in the amount of lens movement per unit image plane displacement due to a change in the focal length of the zoom lens. Since the pulse is set to be generated, the comparator circuit 10 can control the focusing lens to move to the in-focus position simply by comparing the two pulses.

Since this invention is configured as described above, it has the effect of simplifying the mechanism when applied to a focusing device for a zoom lens. In addition, the magnitude of the peak value of the output of the light receiving element corresponds to the focal length, and the focus motor is driven based on the relationship between this peak value and the amount of image plane displacement, so the rotation of the focus motor is The influence of variations can be avoided as much as possible. In addition, if the number of generated pulses is increased by increasing the number of threshold level divisions, the control resolution can be further improved.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing an embodiment of this invention, and FIG. 2 is a block diagram of a control circuit according to this invention.
3 to 5 are signal waveform diagrams for explaining the operation of the embodiment shown in FIG. 1, FIG. 3a is a waveform diagram of the output of the light receiving element, and FIG. Figure 4 is a waveform diagram for explaining the pulse generation state when the relative distance between the light emitting element and the light receiving element is small, and Figure 5 is a waveform diagram for explaining the pulse generation state when the relative distance between the light emitting element and the light receiving element is large. FIG. 3 is a waveform diagram for explaining a pulse generation state. 1...Zoom ring, 1a...Cam groove, 2...
Light emitting element, 3... Light receiving element, 4... Focus motor, 5... Slit disk, 6... Gear, 7...
Focus ring, 8... Threshold level setting circuit, 9... Pulse generation circuit, 10... Comparison circuit, 11... Image plane displacement amount information circuit, 12... Motor drive circuit.

Claims (1)

[Claims for Utility Model Registration] (1) A light-emitting element and a light-receiving element that are provided facing each other and whose relative distance changes in response to changes in the focal length of the zoom lens, and a focusing lens within the zoom lens. is driven by a focus motor that drives
a slit plate that intermittently blocks the optical path between the light emitting element and the light receiving element; and the amplitude changes sinusoidally due to the intermittent blocking of the optical path by the slit plate, and the amplitude changes due to the change in the relative distance. A control information retrieval device for a zoom lens, comprising a pulsing circuit that divides the output signal from the light receiving element at a plurality of threshold levels and outputs pulses. (2) Retrieval of information for control of a zoom lens according to claim 1, wherein the relative distance between the light emitting element and the light receiving element increases or decreases as the focal length increases or decreases. Device. (3) The threshold level is set so that the ratio of the number of pulses to the amount of image plane displacement is constant at any focal length. Information retrieval device for controlling zoom lenses.