JPS60225813A - Automatic focus adjusting device - Google Patents

Abstract

PURPOSE:To improve the precision of automatic focusing by providing a projection optical system or photodetection optical system with a neutral density (ND) filter which is associated operatively with a focusing drive member for a photographic lens. CONSTITUTION:Light for automatic focusing from a light source 1 is passed through a projection lens 2, guided to the photographic lens in a focus ring 5 by mirrors 3 and 4, and projected on a subject S. Reflected light from the subject S is passed through a photodetection lens 6 and transmitted through the ND filter 7 to reach a photodetecting element 8. The photodetecting element 8 consists of two upper and lower elements and is slanted by a cam together with the photodetection lens 6 according to the rotation of the focus ring 5. Then, a focusing state is obtained while the focus ring 5 slants the elements so that their output difference is zero.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an automatic focus adjustment device for adjusting the amount of light incident on a light-receiving element in a light-receiving optical system in a so-called active autofocus camera having a light-emitting optical system and a light-receiving optical system. be.

For example, in conventional active autofocus cameras that use near-infrared light for auto-destruction purposes, when trying to extend the maximum reach distance to a more distant subject, the amount of near-infrared light emitted toward the subject must be increased. I had to. However, if the amount of light emitted per flash is too large, the reflected light from the subject will become too strong when a subject with high reflectance is close, and the amount of light incident on the light receiving element will exceed the range of linear response, causing the light receiving element to This results in saturation of the output and a decrease in the accuracy of automatic spoilage.

In order to improve this, a device is used that controls the amount of light emitted according to the amount of light received by the light receiving element. With this device,
This improves the accuracy of automatic ruining when the subject is close, but it has the disadvantage of making the electronic circuit more complicated. Furthermore, since only the autofocus light is unilaterally weakened with respect to external light, there is a concern that the S/N ratio may deteriorate.

The object of the present invention is to eliminate the above-mentioned drawbacks: ND filter (
Neutral Density Filter).

The object of the present invention is to provide an automatic focus adjustment device that reduces the amount of light emitted or received by the function of the ND filter at short distances, thereby preventing saturation of the light receiving element and improving automatic focusing accuracy. is an active autofocus device that has a light projection optical system that projects light onto a subject and a light reception optical system that receives reflected light from the subject.
The present invention is characterized in that the light projecting optical system or the light receiving optical system is provided with an ND filter that is linked to a focusing drive member of the photographing lens.

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

FIG. 1 shows an active autofocus mechanism to which the present invention is applied, in which autofocus light emitted from a light source 1 passes through a projection lens 2 and is guided by a mirror 3.4 to an imaging lens in a focus ring 5. Light is projected onto the subject S. The reflected light from the subject S passes through the light receiving lens 6, passes through the ND filter 7, and reaches the light receiving element 8. The light-receiving element 8 is composed of two elements, upper and lower, and is tilted up and down together with the light-receiving lens 6 by a cam as the focus ring 5 rotates.

A focused state can be achieved with the focus ring 5 tilted so that the output difference between the respective elements becomes zero.

The ND filter 7 has a continuous density such as a transmittance t with respect to the rotation angle θ of the focus ring 5 shown in FIG. 2(a), and is bonded around the focus ring 5.

This method of adhesion is such that when the focus ring 5 is in a state of focusing at a short distance, the reflected light is more concentrated on the ND filter 7.
It is designed to pass through areas with low transmittance.

In the above-mentioned embodiment, the continuous density ND filter 7 was used, but since it does not necessarily have to be continuous density, the ND filter 7 shown in FIG.
) and (C), the density may vary stepwise other than the continuous density, or an ND filter 7 having two-step density characteristics may be used.

Also, how does the focusing drive member and the ND filter 7 interlock?
Although the method of adhesion was adopted, various other methods can be considered as shown in FIGS. 3 and 4. That is, in the mechanism shown in FIG. 3, a tooth profile 5a is formed around the focus ring 5,
When the focus ring 5 rotates via the teeth 7a provided on the ND filter 7, the ND filter 7 reciprocates. Further, in the mechanism shown in FIG. 4, when the focus ring 5 rotates, the stop portion 7b of the ND filter 7 is pushed by the protrusion 5b provided on the focus ring 5, and the ND filter 7
is arranged to rotate around a rotation center 9.

In any case, the interlocking means is a problem if the movement of the focusing drive member changes the positional relationship between the ND filter 7 and the reflected light from the subject S, and reduces the amount of light that reaches the light receiving element 8 at a short distance. There isn't. Further, in the above-described embodiment, the ND filter 7 acts on the light receiving optical system, but it may act on the light projecting optical system. In Figure 1,
This can be easily understood by reversing the optical path of the autofocusing light and considering B, which is surrounded by dotted lines, as a light projecting optical system and A as a light receiving optical system.

In the embodiment shown in FIG. 1, the light receiving element 8 is tilted up and down, but it is also possible to tilt the light emitting direction or both. Furthermore, instead of providing a tilt, the optical axis may be provided with a vertical movement amount. Furthermore, if a position detection element is used, there is no need to apply tilt or movement. In addition, in the embodiment, only the received light flux passes through the photographing lens.
There are active autofocus systems, but conversely, there are TTL methods in which only the emitted light beam passes through the photographic lens, TTL methods in which all light beams pass through the photographic lens, and external method in which none of the light beams passes through the photographic lens. The present invention can also be implemented with active autofocus.

In this way, the automatic focus adjustment device according to the present invention has a focus adjustment system that operates in conjunction with the focusing drive member even when the subject is at a short distance.
Due to the simple structure of arranging the D filter, the output of the light receiving element does not become saturated and the automatic focusing accuracy is improved. Furthermore, when the ND filter is used in the light-receiving optical system, the S/N ratio between external light and reflected light from the object does not deteriorate, so the problem of deterioration of automatic focusing accuracy due to deterioration of the S/N ratio can be solved.

[Brief explanation of the drawing]

The drawings show an embodiment of an automatic focusing device according to the invention,
Figure 1 is its configuration diagram, Figure 2 (a), (b), (c
) is a characteristic diagram of the ND filter, and FIGS. 3 and 4 are configuration diagrams of the interlocking of the focusing optical system and the ND filter. Reference numeral 1 designates a projection light source, 2 a projection lens, 5 a focus ring, 6 a light receiving lens, 7 an ND filter, and 8 a light receiving element. Patent Applicant Canon Co., Ltd. Attorney Yukihiko Dohibiya Figure 2 Figure 3 Figure 4

Claims (1)

[Scope of Claims] 1. In an active autofocus device having a light projecting optical system that projects light onto a subject and a light receiving optical system that receives reflected light from the subject, the light projecting optical system or the light receiving optical system has a . An automatic focus adjustment device, characterized in that an ND filter is provided in conjunction with a focusing drive member of a photographic lens. 2. The automatic focusing device according to claim 1, wherein the ND filter changes its transmittance characteristics in accordance with the movement of the focusing drive member.