JPH01112212A - Light projecting device for autofocusing - Google Patents

Abstract

PURPOSE:To project a sharp projection image at a short distance as well as a long distance by arranging a longitudinally long-sized light source at a slant angle to the optical axis of a projection lens. CONSTITUTION:A light emitting diode (LED) 12 has plural LED chips arranged to have a longitudinally long-sized shape and is so inclined and arranged that its lengthwise direction and the direction orthogonal to the optical axis of the projection lens form an angle theta. That is, the installation position, the length, and the angle theta of inclination of the LED 12 are so set that the light emitted from the LED 12 passes a projection lens 14 and a cover lens 16 to form a projection image 18 in a focus detectable range L on the optical axis of a photographic lens. Consequently, the projection image 18 on the optical axis of the photographic lens out of the projection image 18 projected onto an object is always in focus, and a light reception area A of a focus detecting line sensor provided in the center part of a photographic screen 29 including the optical axis of the photographic lens receives the projection image being in focus.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an autofocus light projecting device 1, and is particularly applicable to an autofocus device 1 such as a camera, which projects light in a specific pattern onto a subject surface. The present invention relates to an autofocus light projector.

[Conventional technology]

In general, autofocus devices that detect focus using a phase difference detection method or the like cannot obtain sufficient object information when the object has low illuminance and low contrast, resulting in a decrease in focus detection accuracy. Therefore, conventionally, light emitting diodes (LEDs) are made to emit light when the illuminance is low or when the contrast is low. A striped contrast pattern consisting of a transparent part and an opaque part is arranged in front of the LED, and projects a striped pattern onto the subject surface. This actively adds contrast to the subject, making it possible to detect the focal point with high precision even for subjects with little contrast. Note that there is also a method in which LEDs are arranged in a vertically long manner without using a contrast pattern, and the emitted elongated light is used as projection light.

By the way, since it is not known where the subject is located on the optical axis of the photographic lens, the projected light beam has a certain spread and irradiates a predetermined light projection range (for example, 1 m to 5 m>).

[Problem that the invention seeks to solve]

However, since conventional light projection devices are configured so that the projected light is focused at approximately the center of the light projection range (for example, 3 m), the subject may be closer than the imaging position of the projected light. If the distance is too high or too far away, the projected image becomes blurred, making it impossible to obtain sufficient object information (clear contrast), resulting in a decrease in focus detection accuracy.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an autofocus light projection device that can project a sharp projected image over a short distance to a long distance on the optical axis of a photographing lens. shall be.

[Means for solving problems]

In order to achieve the above object, the present invention provides an autofocus system that projects light from a vertically elongated light source located at a certain distance from the optical axis of the camera's photographing lens onto the subject surface through a projection lens. In the light projection device for commercial use, among the vertical projection light beams projected from the light source through the projection lens, the upper light projection pattern projected toward the long distance side is imaged at a long distance position, and The lower light projection pattern that projects light toward the distance side is characterized in that the light source is arranged at an angle with respect to the optical axis of the light projection lens in order to form an image at a short distance position.

[Effect]

According to the present invention, the light source is arranged at an angle with respect to the optical axis of the light projection lens, and the upper light that illuminates the far side from the light source through the light projection lens is focused at a long distance position, and The lower light illuminating the side is imaged at a short distance position, and a projected image is formed over the entire light projection range on the optical axis of the photographing lens.

〔Example〕

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of an autofocus light projecting device according to the present invention will be described in detail below with reference to the accompanying drawings.

First, an example of a method for detecting a focus based on the amount of information such as the contrast of a subject will be briefly described. Fourth
The figure is a schematic diagram of a focus detection optical system using a phase difference detection method, and the image formed by the photographic lens 30 is focused on the film or the like through the field lens 32 and the re-imaging lenses 33 and 34. CCD line sensor 35A=
35B.

Light receiving area (distance measurement area) of line sensors 3, 5A, 35B
Δ is provided at the center of the photographing screen 29 as shown in FIG. 5, and the band-shaped projected image B, which is, for example, the light emission pattern of a vertically long LED, falls within the distance measurement area A of the line sensors 35A and 35B. The optical system of the autofocus light projector is constructed as follows.

Now, if the projected image by the LED is projected onto a subject with no contrast, the line sensors 35A and 35B
outputs photoelectric output waveforms A and B as shown in FIG. 6, for example. If the waveforms A and B match and overlap, it means that the focus is on, and if they are out of focus, then the out-of-focus state is detected from the amount and direction of the out-of-focus. Note that the detection of the amount of deviation of the waveform A1B is performed by a known correlation calculation, and its explanation will be omitted here.

FIG. 1 is a schematic diagram showing a camera equipped with an autofocus light projection device according to the present invention and its optical system. In the figure, numeral 10 is an autofocus light projecting device, and L
It is composed of an ED 12, a light projection lens 14, and a cover glass 16.

The light emitted from the LED 12 is projected through a projection lens 14 and a cover lens 16 with a spread of a predetermined projection light angle α. That is, the light is projected so as to illuminate a subject within a focus detectable range (for example, a range of 1 m to 5 m) L on the optical axis of the photographing lens 20 of the camera.

The light reflected from the subject enters the ΔAF sensor 26 via the photographing lens 20, mirror 22, and submirror 24, and the AF sensor 26 detects the projected contrast pattern. Note that the light reflected by the mirror 22 enters the pentaprism 28 of the finder.

FIG. 2 is an enlarged view of the optical system of the autofocus light projector shown in FIG. 1. As shown in the figure, LED12
A plurality of LED chips are arranged side by side to form a vertically elongated shape, and are arranged at an angle such that the angle between the longitudinal direction and the direction orthogonal to the optical axis of the light projecting lens is θ. That is, L
The light emitted from the ED 12 passes through the projection lens 14 and the cover lens 16 to the LE so that a projected image 18 is formed over a focus detectable range on the optical axis of the photographic lens.
The installation position, length, and inclination θ of D12 are set.

Therefore, among the projected images 18 irradiated onto the subject,
The projected image 18 on the optical axis of the photographing lens is always in an imaging state,
As shown in FIG. 3, a photographing screen 29 including the optical axis of the photographing lens
A line sensor 35A for focus detection provided in the center of the
, 35B (FIG. 5) can receive the formed projection image.

In addition, since FIG. 3 shows the shooting screen when the subject is located at approximately the center position (approximately 3 m) of the focus detectable range, the lower projected images 18A and 18A formed at a shorter distance than that position Upper projected image 18 formed at a distance from that position
B becomes a blurred image.

In this way, the projected image is formed over the entire focus detectable range on the optical axis of the photographing lens, resulting in a sharp projected image at least in the light-receiving area that receives subject information for focus detection. is obtained, and focus detection accuracy is improved.

Next, the installation position, inclination angle, etc. of the LED will be considered.

In Fig. 1, if the focus detectable range is 1m to 5m from the photographic lens and the height H of the LED 12 from the photographic lens optical axis is approximately 100+n+n, the optical axis of the photographic lens and the light emitting lens are The angle β formed is 2'' to 3 degrees.

Since the angle β formed by both optical axes is small in this way, the focus detectable range L (the length of the projected image 18 on the photographing lens optical axis) is projected onto the projection lens optical axis, as shown in FIG. The range L' is approximately equal to the range, and the distance a from the projection lens 14 to the nearest imaging position of the projection image 18 and the distance a' from the farthest imaging position can be 1 m and 5 m, respectively. can. Further, the distances from the light projection lens 14 to the light source necessary to form images at distances a and a' are respectively b and b', and the focal length f of the light projection lens 14 is 20+
nm, then from the following formula, the distances and b' are, respectively, b = 20,408 mm, b' = 20.080
+nm.

That is, if the LED 12 is arranged so that the upper end position of the LED 12 is located at a distance of 20.408 mm from the light projection lens 14, and the lower end position of the LED 12 is located at a position of 20,080 mm from the light projection lens 14, the above-mentioned result can be achieved. Projection image 1
8 is obtained.

Further, the inclination angle θ of the LED 12 has the following relationship with the difference Δb between the distances b and b' and the length 1 of the LED 12. Therefore, for example, assuming that the length β of the LED 12 is 3 mm, and substituting the difference Δb=b−b′=0.328 mm into the above-mentioned (2), the inclination angle θ is obtained.

In this embodiment, an elongated light source is used, but the present invention is not limited to this. For example, a light source having a certain size in the vertical direction and a contrast pattern placed in front of the light source may also be used. The invention is applicable.

〔Effect of the invention〕

As explained above, according to the autofocus light projecting device according to the present invention, by arranging the vertically elongated light source at an angle with respect to the optical axis of the light projecting lens, it is possible to The upper light that illuminates the side can be imaged at a far-distance position, and the lower light that illuminates the near-distance side can be imaged at a short-distance position. This allows the projection image to be formed over the entire light projection range on the optical axis of the photographing lens.
Regardless of the position of the subject, a sharp projected image, that is, more subject information for focus detection can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing a camera equipped with an autofocus floodlighting device according to the present invention and its optical system, and FIG.
FIG. 3 is an enlarged view of the optical system of the autofocus light projector shown in the figure, FIG. A schematic diagram of a focus detection optical system that detects the focal position; FIG. 5 is a diagram showing the relationship between the distance measurement area within the photographic screen and the projected image;
FIG. 6 is a diagram showing an example of a photoelectric output waveform of a line sensor. 10... Autofocus floodlight device, 12...
・LED, 14...Light projection lens, 16,・
...Cover glass, 20...Photographing lens, 2
6...AF Sens.

Claims (1)

[Claims] In an autofocus light projector that projects a specific pattern of light onto a subject via a light projector lens from a vertically elongated light source placed a certain distance from the optical axis of a camera's photographing lens. , Of the vertical projection light beams projected from the light source through the projection lens, the upper light projection pattern projected toward the long distance side is imaged at a long distance position, and the light is projected toward the short distance side. 2. An autofocus light projecting device, characterized in that the light source is arranged at an angle with respect to the optical axis of the light projecting lens so that the lower light projection pattern is formed at a short distance position.