JPS62106424A - Optical system for focus detection - Google Patents

Abstract

PURPOSE:To make the whole of a lens compact while keeping the focus detection precision in the conventional TTL distance measuring system by constituting independently an optical system for focus detection in the peripheral part of a photographic focus lens. CONSTITUTION:Optical axes of a focus lens 24 for light projection and a focus lens 25 for light reception coincide with an optical axis O of the photographic lens, and these lenses 24 and 25 are provided in the peripheral part of a focus lens 21 apart from each other and are joined with the focus lens 21 into one body to constitute a focus lens unit 20. They are moved as one body in the direction of an arrow to perform focusing, and a projected light spot in the in-focus state is placed in the center of the photographic picture to constitute a system having no parallax. A light emitting element 22 and a light receiving element 27 are fixed in positions optically conjugate to a focus F21 of the focus lens 21, and a light shielding plate 33 which prevents the direct light leak from the light emitting element 22 to the light receiving element 27 is provided between them.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention projects near-infrared light toward a subject from a lens side, receives the reflected light with a light receiving element, and focuses the photoelectric conversion signal. The present invention relates to a so-called active type focus detection optical system that detects.

<Conventional technology> Conventionally, this type of optical system has two methods: one is the so-called external distance measuring method, in which a light emitting lens and a light receiving lens are provided outside the photographing lens, and the other is a so-called external distance measuring method, in which both lenses are provided inside the photographing lens. It is broadly classified into the so-called TTL distance measuring method, in which all of the light beam passes through a part of the photographing lens.

The external distance measurement method measures distance based on the principle of triangulation by mechanically moving the light receiving element or light emitting element in conjunction with the focusing operation of the photographic lens. An error occurs.

Therefore, in order to maintain distance measurement accuracy, a certain amount of base line length is required, and there is a limit to miniaturization.

Another type of external ranging method is PSD (Posi
There are some devices that use a 5-sensitive device as a light-receiving element. This does not require moving the light-receiving element or the light-emitting element, but since there is a limit to the linearity of the position detection characteristics, this also requires a certain baseline length, which also limits miniaturization. .

On the other hand, to explain an example of the TTL distance measuring method shown in FIG. 6, the photographing system includes a focus lens 1° variator 8.
Convencator9. Afocal lens 10. Aperture 11
A zoom lens optical system is constituted by a lens 12 and a lens 12, so that an image is formed on an imaging plane F, and a 1llll lens system is configured such that the light from the light emitting element 2 is transmitted through a projection lens 3 and a total reflection mirror 4f: The reflected light is projected onto the subject through the outer circumference of the focus lens 1, and the reflected light passes through the outer circumference of the focus lens 1 again to a total reflection mirror 5 and a receiver; The light is received as a spot image. Here, the light emitting element 2 and the light receiving element 7 are arranged at a position optically conjugate with the focal point F1 of the focus 1/lens 1. and,
When the focus lens 1 is in focus relative to the subject, the light emitting spot image P on the light receiving element 7 is shown in FIG. 7 (b'
When the light receiving element 702 is located at the center of the light receiving element ear as shown in FIG.
Shift focus lens 1 based on pixel difference signal or d:ratio signal
This constitutes an automatic focus adjustment device that drives the lens to bring it into the focused state shown in FIG. 7(b).

<Problems to be Solved by the Invention> By the way, in the TTL distance measurement method described above, there is no movable part other than the focus 1/lens 1, and there is no need to use a PSD. Therefore, the base line length (corresponding to the exit pupil interval of the projected and received light beams in the focus lens) can be shortened, and the system can be made compact. However, in order to pass the projected and received light beams through the focus lens, a focus lens with a large diameter is required, which increases the weight and is disadvantageous in terms of cost.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate all of the drawbacks of the prior art and provide a light, compact, and highly accurate active focus detection optical system.

Means for Solving the Problems> The structure of the present invention for achieving the above-mentioned object will be explained using FIG. 1 and FIG. 2, which correspond to embodiments.

The present invention provides a pair of focus detection lenses 24 and 25 having a focal length equal to the ml/l dance around the periphery of the focus 1 lens 21 which is movable in the optical axis direction for focus adjustment. A light emitting element 2 is provided on the focal plane side of the 1/lens 24 and 25, respectively.
2 and a light receiving element 27 are fixedly installed.

<Operation> The light from the light emitting element 22 passes through the entire lens 24 and is projected onto the subject, and the reflected light passes through the entire lens 25 and is projected onto the light receiving element 27.
The focus lens 2
1 and lenses 24 and 25 are driven to detect the in-focus position. As shown in the front view of the focus I/lens 21 and the lens 24°25 in FIG. 2, the focus lens 21 There is no need to increase the diameter of the lens for focus detection, making it possible to create a small-diameter, lightweight focusing lens.

<Example> Hereinafter, a zoom 1/lens optical system using an example of the present invention will be described with reference to FIGS. 1 and 2.

The zoom lens photographing optical system includes a focus I/lens 21° variator 28. Compensator 29. Affocal lens 30. It is composed of an aperture 31 and a 1-no-lens 32, and is configured to form an image on an imaging plane F.

On the other hand, in the focus detection optical system, the light projection system includes the light emitting element 22,
It consists of a light projection lens 23 and a light projection focus lens 24. The light projection focus lens 24 is a lens having the same focal length as the focus lens 21, and the light projection lens 23 shortens the combined focal length of the light projection system. This is to reduce the F number and increase the light emitting power, and at the same time, the light receiving system is equipped with a light receiving focus lens 25. It is composed of a light receiving lens 26 and a light receiving element 27 formed from two pixels, and the light receiving focus 1/
The lens 25 has the same focal length as the focus lens 21, and the light-receiving lens 26 shortens the combined focal length of the light-receiving system to achieve compactness. The light emitting focus lens 24 and the light receiving focus 1/lens 2
5, whose optical axis coincides with the optical axis O of the photographing lens, is provided integrally with the focus lens 21 at the periphery of the focus lens 21 at a distance from each other, and constitutes the focus lens unit 20, as indicated by the arrow in FIG. The light emitting element 22 and the light receiving element 27 are positioned at the focal point F2. A light-shielding plate 33 is fixed at a position optically conjugate with the pixel element and is provided between the pixel elements to prevent direct leakage of light from the light-emitting element 22 to the light-receiving element 27.

This focus lens 21 is a conventional TTL type focus lens 1 indicated by a two-dot chain line as shown in FIG.
Compared to the size of the lens, its diameter is small, so there is no need to make it large for focus detection, resulting in a small-diameter, light-clear focus lens. Further, the light emitting focus lens 24 and the light receiving focus lens 24 are partially cut out from a large lens having a radius R5 centered on the optical axis 0.

3 to 5 show other embodiments of the holding structure for the focus detection optical system of the present invention. In this embodiment, the focus lens 21 for photographing has three lenses 2.
1a, 21b, and 21c, and a focus lens 24 for projecting light and a focus lens 25 for light reception are integrally held together with a focus lens 21 in a focus barrel 41 around the periphery thereof, and the focus barrel 41 is attached to a guide bar 42. is inserted and fixed parallel to the optical axis direction, and the guide bar 42 is guided through the lens barrel base plate 43, 44, and is driven in the direction of the arrow in FIG. 4 to perform focusing. Further, as shown in FIG. 5, behind the light-receiving focus lens 25, a light-receiving lens 26 and a light-receiving element 27 are fixed to a light-receiving system holder 45 fixed to the lens barrel base plate 43. As for the light projection system, a light projection lens and a light emitting element are fixed behind the light projection focus lens 24 similarly to the light reception system.

In each of the above-mentioned embodiments, aspherical lenses made of plastic may be used as the light emitting focus lens 24 and the light receiving focus lens 25 of the focus detection system, in which case 1 is a photographic focus lens. As well as being more compact, the overall structure can be made lighter, more compact, and at lower cost. In addition, a focus lens for projecting light 24 and a focus lens for light reception 25 f 1
It may be composed of multiple units.

<Effects of the Invention> As explained above, the present invention improves the focus detection accuracy of the conventional TTT and distance measuring methods by configuring the focus detection optical system separately in the periphery of the photographic focus lens. This has the effect of making the entire men's clothing compact while maintaining the same.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram of an embodiment of a zoom lens optical system using a focus detection optical system according to the present invention, FIG. 2 is a front view of the main parts thereof, and FIG. 3 is another embodiment of the present invention. Main part front view,
Fig. 4 shows line 31'l A-A, 20...Focus lens unit, 21...Focus lens, 22...
- Light emitting element, 23... Light emitting lens, 24... Focus lens for light emitting, 25... Focus lens for light receiving,
26... Light receiving lens, 27... Light receiving X element, 28...
・Variator, 29...Convencator, 30...
Afocal lens, 31... Aperture, 32... Relay lens, 33... Light shielding plate, 41... Focus tube, 42... Guide bar, 43.44... Lens barrel base plate,
45... Light receiving system holder, F... Imaging surface, F2.・・・
・Focus lens focus.禦-k "" Made 1 Conqueror

Claims (1)

[Claims] 1. A focus detection lens having a focal length equal to that of the focus lens is provided at the periphery of a focus lens movable in the optical axis direction for focus adjustment so as to be movable integrally with the focus lens; 1. An active type focus detection optical system comprising a light emitting element and a light receiving element fixed to the focal plane side of a lens.