JPS58158618A - Automatic focus adjusting device - Google Patents

Abstract

PURPOSE:To move a main optical system for photographing to a proper position and to make a speedy adjustment by providing an auxiliary optical system which moves the focusing position of luminous flux incident to a photodetecting element and a means which detects the focusing position by cooperating with the photodetecting element and moves the main optical system for photographing by a necessary extent on the basis of the extent of focus movement by the auxiliary optical system. CONSTITUTION:Luminous flux Lb passed through a rotary reflecting mirror 2 is deflected downward by an auxiliary reflecting mirror 8 provided to the back surface of the rotary reflecting mirror 2 to strike the auxiliary optical system 9, a light-splitting prism 10, and plural line sensors 11 arranged along the optical axis. The auxiliary optical system 9 is moved in an optical-axis direction by the 1st rack and pinion mechanism 13 driven by the 1st motor 12, which is controlled by the output signal of a signal processing circuit 14 which processes output signals from the line sensors 11. The signal processing circuit 14 sends out the output signal calculated on the basis of the movement extent of the auxiliary optical system 9 to the 2nd motor 15, which moves a photograhic lens 1 in its optical-axis direction through the 2nd rack and pinion mechanism 16.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an automatic focus adjustment device that can be suitably used in a so-called TTL automatic focus camera that performs focusing using a light beam transmitted through a photographic lens.

This type of autofocus camera, which has been known in the past, uses a method of detecting the focal position of a light beam from an object by moving a photographing lens. However, this method has disadvantages in that focusing is slow or the load on the electric motor for moving the photographic lens increases because the heavy photographic lens is moved while distance measurement is being performed.

The purpose of the present invention is to eliminate the drawbacks of conventional focusing devices,
A small and lightweight auxiliary optical system is placed separately from the main photographing optical system consisting of the photographic lens, etc., and signals based on this auxiliary optical system are used to move the main photographing optical system to an appropriate position and make quick adjustments. Moreover, the object is to provide an automatic focus adjustment device that places less load on the electric motor, and its content is to move the focal position of the light beam incident on the light receiving element between the main photographing optical system and the focus detection light receiving element. means for inserting an auxiliary optical system, detecting a focusing position difference by cooperation of the auxiliary optical system and the light receiving element, and moving the main photographing optical system by a required amount based on the amount of focus movement by the auxiliary optical system; It is characterized by having the following.

The present invention will be explained in detail below based on illustrated embodiments.

In Fig. 1, reference numeral 1 denotes a photographic lens, and a beam of light incident through the photographic lens 1 is divided into two directions by a rotating reflecting mirror 2 whose central portion is semi-transparent or partially transparent. Ru. That is, the light beam La reflected in the - direction by the rotating reflector 2 passes through the focusing plate 3, condenser lens 4, pentaprism 5, and eyepiece lens 6, which are arranged sequentially along the optical axis, and is seen by the naked eye. be observed. On the other hand, the light beam Lb that has passed through the rotary reflector 2 is deflected downward by the auxiliary reflector 8 provided on the back surface of the rotary reflector 2.
The light is configured to enter an auxiliary optical system 9, a light splitting prism 10, and a plurality of line sensors 11 arranged along the optical axis. The auxiliary optical system 9 is moved in the optical axis direction by a first rack and pinion mechanism 13 driven by a first electric motor 12.
2 is controlled by the output signal of a signal processing circuit 14 that processes the output signal from the line sensor 11. Further, the signal processing circuit 14 sends an output signal calculated based on the movement value of the auxiliary optical system 9 to the second electric motor 15, and the second electric motor 15 drives the second rack and pinion mechanism 16.
The photographic lens 1 can be moved along its forward axis via the lens.

Therefore, the light beam Lb that passes through the photographing lens 1, the rotary reflector 2, and the auxiliary reflector 8 is used for focus adjustment, and the light beam Lb passes through the auxiliary optical system 9 and passes through the light splitting prism 10 into a plurality of light beams with different optical path lengths. The line sensor 11 and the signal processing circuit 14 perform focus determination. If it is in focus, there is no need to move the photographing lens 1, but if it is not in focus, the first electric motor 12 is controlled by the output signal of the signal processing circuit 14, and the auxiliary optical system The in-focus state is determined without moving the lens 9, the amount of extension of the photographic lens 1 is calculated from the amount of movement, and the second electric motor 15 drives the photographic lens 1 to an appropriate position.

In particular, when automatic focusing using a blurred image is adopted as the focus detection means as in the embodiment, in order to process the distance measurement signal while the auxiliary optical system 9 is moving, the heavy photographic lens 1 must be directly moved. There is no need to determine the in-focus state, and smooth and quick focusing becomes possible.

FIG. 2 shows another embodiment of the auxiliary optical system 9. As the auxiliary optical system 9, an optical system called an Alvarez whose focal length changes by lateral shift is used. In this case, the amount of movement of the auxiliary optical system 9 is determined by the amount of movement of the auxiliary optical system 9.
It is determined as the amount of relative movement of the optical members 9a and 9b perpendicular to the optical axis.

Further, as a modification of the above embodiment, a liquid crystal lens element whose power can be electrically changed may be used as the auxiliary optical system 9, or the auxiliary optical system 9 consisting of a lens may be removed, and the auxiliary reflecting mirror 8 may be replaced with a pimol mirror, etc. It is also possible to electrically determine the amount of focus movement as a variable power concave surface of There is no problem in adopting this method.

As explained above, the automatic focus adjustment device according to the present invention has
When adjusting the focus, instead of putting the heavy photographic lens into the feedback loop of the focus detection system, first move the small and lightweight auxiliary optical system, and then move the photographic lens by an amount that is uniquely determined based on the amount of movement. This has the advantage that quick focus detection is possible and less power is required.

[Brief explanation of the drawing]

The drawings show an embodiment of an automatic focusing device according to the invention,
FIG. 1 is a configuration diagram thereof, and FIG. 2 is a configuration diagram with the auxiliary optical system as a separate member. 1 is a photographing lens, 2 is a rotating reflector, 8 is an auxiliary reflector, 9.9a, 9b are auxiliary optical systems, 10 is a light splitting prism, 11 is a line sensor, 12 is a first electric motor, 13 is a rack and pinion 14 is a signal processing circuit, 15 is a second electric motor, and 16 is a rack and pinion mechanism. Patent applicant Canon Co., Ltd. Figure 1

Claims (1)

[Scope of Claims] 1. An auxiliary optical system that moves the focal position of the light beam incident on the light receiving element is inserted between the main photographing optical system and the focus detection light receiving element, and the auxiliary optical system and the light receiving element are 1. An automatic focus and adjustment device comprising means for detecting a focus position in cooperation with an element and for moving the main photographing optical system by a required amount based on the amount of focus movement by the auxiliary optical system. 2. The automatic focus adjustment device according to claim 1, wherein the focal position is moved by the auxiliary optical system by moving a lens system in the optical axis direction. 3. The automatic focus adjustment device according to claim 1, wherein the movement of the focus position by the auxiliary optical system is performed by laterally shifting an optical member having an inclined surface with respect to the optical axis.