1. Field of the Invention
The present invention relates to an optical apparatus that detects an operation of an operation member using a magneto-resistive (MR) element and optical sensor, etc., and controls the driving of an optical element, and to an image-pickup apparatus using this optical apparatus.
2. Description of the Related Art
A lens apparatus (optical apparatus) used for an image-pickup apparatus such as a video camera or digital still camera may be provided with a manual operation ring that gives drive instructions to a drive unit of a variable-power optical element or focusing optical element. In this case, a controller detects an amount of operation or operation direction of the manual operation ring and controls a driving operation of the drive unit, that is, the optical element, according to the detection result.
As an example of a drive control system for optical elements using such a manual operation ring, there is a system constructed of a magnetic scale made up of different magnetic poles, which are arranged with alternating magnetic polarities, and a magnetic sensor facing this magnetic scale in such a way as to move relative to each other in accordance with operation of the manual operation ring, and to control a drive unit based on a count (count value) of a periodic variation (pulse) of a signal output from the magnetic sensor.
FIG. 7 shows an example of a control system utilizing a pulse count of a magnetic (MR) sensor. Reference numerals 20a and 20b in the figure denote output signals of phase A and phase B from the MR sensor, as it moves relative to a magnetic scale, and 20c denotes a reference potential of the controller.
The controller converts the output signals 20a and 20b, output from the MR sensor in accordance with operation of the manual operation ring, to digital (pulse) signals such as 20d (phase A) and 20e (phase B), counts cross points 20f at which the pulse signals 20d and 20e cross the reference potential 20c, and controls the drive unit based on the count value.
FIG. 8 illustrates an example of a control system that divides the output signal of the MR sensor at intermediate positions arbitrarily (intermediate separation control system). Reference numerals 20a and 20b denote output signals of phase A and phase B from the MR sensor as it moves relative to the magnetic scale, and 20c denotes a reference potential of the controller.
The controller extracts a portion 20h of good linearity (20f is an upper threshold of the linear portion 20h, and 20g is a lower threshold of the linear portion 20h) of the output signals 20a and 20b from the MR sensor, and divides this linear portion 20h by an arbitrary number, for example, 20 or 50. Then, the controller controls the drive unit based on the signal value obtained during operation of the manual operation ring.
In order to improve resolution of the stop position of a variable-power optical system or a focusing optical system, it is necessary to improve detection resolution of the rotation position of the manual operation ring. Here, according to a pulse count control system using the MR sensor, the resolution of the rotation position of the manual operation ring is determined by the pitch of a detection magnet of the MR. sensor. For this reason, improving the resolution of the rotation position requires the magnet pitch to be reduced.
However, there is a limit to work (manufacture) for reducing the magnet pitch and it is difficult to further reduce the actual pitch. Thus, it is difficult to drastically improve the resolution of the rotation position of the manual operation ring. It is also possible to consider a method that provides several stages of gear between the manual operation ring and the magnetic scale to mechanically improve the resolution, but this would lead to an increase in size of the apparatus.
On the other hand, the control system realized through intermediate division of the output signal of the MR sensor improves the resolution but complicates the processing of the control circuit and slows down the processing speed. Moreover, the user rotates the manual operation ring at high speed mostly for the purpose of moving optical elements close to a desired position at high speed without questioning segmentation of the resolution of stop positions of the optical element.
It is an object of the present invention to provide an optical apparatus, and an image-pickup apparatus provided with this optical apparatus, capable of reducing the processing burden on a controller, driving the optical element at high speed and improving the resolution of stop positions.
In order to attain the above-described object, the optical apparatus, which is one aspect of the present invention, includes a movable optical element, a drive unit that drives the optical element, an operation member manually operated to instruct a driving operation of the optical element, a signal output unit that outputs a signal that varies periodically according to operation of the operation member, and a controller that controls the drive unit based on a signal from the signal output unit. The controller determines the operation speed of the operation member based on the signal from the signal output unit, and determines whether to control the drive unit based on a count of periodical variations of the signal from the signal output unit or to control the drive unit based on the value of the signal from the signal output unit.
Furthermore, an image-pickup apparatus of the present invention includes the optical apparatus constructed as described above and a photoelectric conversion element that photoelectrically converts the image of an object formed by the optical apparatus.
The features of the optical apparatus and image-pickup apparatus of the present invention will become more apparent with reference to the following detailed description of preferred embodiments of the present invention taken in conjunction with the accompanying drawings.