JPH028516B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a focus detection optical system for performing automatic focus adjustment in a photographing device.

Imaging devices such as image pickup tubes of photographic equipment such as television cameras and electronic still cameras, or solid-state imaging devices using CCDs, etc., convert an optical image into an electrical quantity, accumulate it as a charge pattern, and store this charge pattern. It has the function of scanning and reading.

Therefore, on the imaging surface of this imaging device,
If it is possible to form an optical image by the photographing optical system and an optical image for focus detection at the same time, it becomes unnecessary to provide a special photoelectric conversion device and its drive device for focus detection, making it possible to create an inexpensive and simple photographic device. It is expected that an automatic focus adjustment device will be developed.

An object of the present invention is to provide a focus detection optical system for a photographing device to realize this.

Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a perspective configuration diagram showing an optical system of an embodiment in which the present invention is applied to a television camera. The photographing optical system of a television camera generally consists of three zoom lens groups consisting of a focus lens group 1, a variable magnification lens group 2, and an imaging lens group 3 as shown in the figure. An optical image is formed on the imaging surface 4a of the imaging device 4 and converted into an electrical signal.

Incidentally, in a photographing optical system using such a zoom lens, the photographing light beam is generally arranged to become a parallel beam of light when focused between the variable magnification lens group 2 and the imaging lens group 3.

Therefore, in this embodiment, a half mirror 5 is interposed as a light splitter between the variable magnification lens group 2 and the imaging lens group 3, and a part of the photographing light beam is divided and taken out upward. Mirrors 6, 7, and 8 serve as optical deflectors to deflect and guide the light by 90 degrees, and
A pair of lenses 9, 10 and 9', 10', which are a pair of lens systems, are provided between the mirrors 6 and 7, and the imaging device 4
A pair of images is formed on a part of the imaging surface 4a of the camera.

In this case, the imaging position of the pair of images is the imaging surface 4a
The blanking part is the part outside the shooting screen above, so that it does not affect the shooting screen.

Next, as shown in FIGS. 2a, b, and c, the focus detection optical system 5 is
The states of the pair of images by 10 and 9' and 10' will be explained.

When the photographing system is in focus, assuming that the light beams emitted from the variable magnification lens group 2 are parallel, the distance between the pair of images A and B is determined by the distance between the lens systems 9 and 10 as shown in FIG. is equal to the distance D between the lens systems 9' and 10'.

Next, since the light beam emitted from the variable magnification lens group 2 when the photographing system is in the front focus becomes a convergent light beam, the pair of images A and B are different from the focused image in FIG. As shown in b, they shift inward and become blurred.

Furthermore, when the shooting system is rear focused, the variable magnification lens group 2
Since the luminous flux emitted from the is a diverging luminous flux, the pair of images A and B are compared to the focused image in Fig. 2a,
As shown in c in the same figure, they shift outward and become blurred.

Therefore, by calculating the photoelectrically converted outputs of the pair of images A and B and determining the deviation x from the position in the focused state, front focus, rear focus, and focus are determined. The focus lens 1 can be moved and displayed so that the focusing operation is automatically performed.

Furthermore, even in a photographing optical system where the light flux emitted from the variable magnification lens group in the focused state is not a parallel light flux, the positions of the pair of images in the focused state are known in advance due to the design of the optical system, so the same method as described above can be applied. Focus detection can be performed.

Furthermore, it is clear from the nature of zoom lenses that in the focused state, the angle of the light beam emitted from the variable magnification system remains constant regardless of zooming.
Regardless of the zooming state, completely similar focus detection and focusing operations can be performed.

[Brief explanation of drawings]

FIG. 1 is a perspective configuration diagram showing an embodiment of the present invention;
2A, 2B, and 2C are diagrams showing the positions of a pair of subject images in each state of focus, front focus, and rear focus in the embodiment of FIG. 1, respectively. 1... Focus lens group, 2... Variable power lens group, 3... Imaging lens group, 4... Imaging device,
5... Half mirror (light splitter), 6, 7, 8...
...Mirror (light deflector), 9, 10, 9', 10'...
...Lens for focus detection optical system.

Claims (1)

[Claims] 1. In an optical system of a photographing device consisting of a focus lens group, a variable magnification lens group, and an imaging lens group, a light splitter that divides a part of the photographing light beam between the variable magnification lens group and the imaging lens group. A focus detection method for a photographing device in which a light beam split by the light splitter is imaged on a portion of the imaging surface of the imaging device outside the photographing screen using a pair of lens systems and a light deflector. optical system.