JPH01303410A - Af camera - Google Patents

Abstract

PURPOSE:To find a range even if an object has a low brightness by retreating an infrared cut filter when an autofocus system becomes lower than a low brightness limit, and thereby finding a range. CONSTITUTION:A camera with a passive AF system which uses a photographing element 5 for a range finding sensor 9 as another purpose has a filter operating device retreating the infrared cut filter 3 installed in a camera optical path. When the brightness of an object is at a normal level, the infrared cut filter 3 is positioned in the optical path of the camera, whereas if the brightness is lower than its limit, the filter operating device retreats the infrared cut filter 3 outside the optical path. As a result, even if it is at night or the brightness of an object is low, a range can be found to enable AF photographing.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an AF (auto focus) camera, and therefore mainly relates to an improvement of an AF system for an electronic still camera.

[Conventional technology]

2. Description of the Related Art Conventionally, AF cameras have been known that measure distance by using an image sensor as a distance measurement sensor. This method takes advantage of the fact that the amount of high frequency components included in the video signal of a photographed image corresponds to the degree of focus, and the focus is adjusted by searching for the peak value of the high frequency components. .

[Problem to be solved by the invention]

In conventional AF cameras that measure distance by using the above-mentioned image sensor as a distance measurement sensor, when the subject brightness is low, such as when shooting at night, most of the video signal becomes saturated, making it difficult to measure distance. It becomes impossible. In order to measure distance in such a state, appropriate illumination is required, and it would be convenient if distance measurement could be performed by, for example, irradiating infrared light instead of visible light.

However, since the sensitivity of the image sensor extends to an infrared light range that cannot be viewed, an infrared cut filter is generally installed in front of the image sensor. Therefore, there is a problem in that even if infrared light is applied from the outside, the irradiation cannot be effective for distance measurement.

The present invention aims to solve the above problems. That is, an object of the present invention is to provide an AF camera in a passive AF system in which an image sensor is also used as a distance measurement sensor, which enables distance measurement even when the subject brightness is low, such as when shooting at night. It is something.

[Means to solve the problem]

In order to achieve the above object, the present invention provides a filter operation device for retracting an infrared cut filter installed in the camera optical path out of the optical path in a camera having a passive AF system in which the photographing element also serves as a distance measurement sensor. With this, when the output of the photometric element installed inside the camera is below the low brightness limit of the AF system, the infrared cut filter is moved out of the optical path and distance measurement is performed.

[For production]

According to the present invention, in a camera having a passive AF system in which the photographing element also serves as a distance measurement sensor, the camera has a filter operation device for retracting an infrared cut filter installed in the camera optical path out of the optical path. In the normal case, place an infrared cut filter in the camera's optical path, and when the subject brightness is below the low brightness limit,
The filter operating device allows the infrared cut filter to be moved out of the optical path. Therefore, distance measurement can be performed even under conditions where the brightness of the subject is low, such as during night photography, and AF photography becomes possible.

〔Example〕

FIG. 1 shows an embodiment of the present invention, and FIG. 2 shows the operation of an infrared cut filter.

In Fig. 1, 1 is an imaging lens, 2 is a total reflection mirror,
3 is a movable infrared cut filter, 4 is a crystal plate, 5 is an image sensor, 6 is a half mirror, 17 is a pentaprism, 8
9 is a finder lens, and 9 is a photometric sensor.

In FIG. 2, 10 is a solenoid, 11 is a spring, and 12 is a central shaft around which the infrared cut filter 3 rotates.

Note that (a) in FIG. 2 shows a state in which the infrared cut filter 3 is in the optical path of the camera, that is, a normal state, and (b) in FIG. 2 shows a state in which the infrared cut filter 3 is removed from the optical path. It shows the state of being.

In the AF camera having the configuration shown in FIGS. 1 and 2, the light beam that has passed through the imaging lens 1 is incident on the pentaprism 7 side by the total reflection mirror 2, and on the way, it is reflected by the half mirror 6. A part of the light enters the photometric sensor 9. This photometric sensor 9 measures the brightness level of this incident light?
+! '1 light is emitted, and a circuit system (not shown) determines whether this value is lower than the low brightness of the AF system.

If it is determined that the brightness level is sufficient for distance measurement with the AF system, after the mirror has been raised, the infrared cut filter 3 can be rotated onto the optical path as shown in (a) of FIG. It is biased counterclockwise by a spring 11 and installed. Therefore, the light beam that has passed through the imaging lens 1 passes from the infrared cut filter 3 through the crystalline lens 4 and forms an image on the imaging element 5, where it can be focused and photographed.

In addition, if the output of the photometric sensor 9 is determined to be below the low brightness limit of the AF system, after the mirror rises, the solenoid 10 pushes the infrared ray cut filter 3 clockwise as shown in FIG. 2(b). The light beam rotates about the central axis 12 and retreats out of the optical path, and the light beam passes through the crystal plate 4 and forms an image on the image sensor 5, where the distance is measured and focused in the infrared region.

At this time, an effective method is to irradiate infrared rays from the external surface to improve distance measurement accuracy. Thereafter, the solenoid 10, which is a filter operating device, is restored, and the force of the spring 11 returns the infrared cut filter 3 to the optical path, and photography is performed by external illumination from a strobe or the like (not shown).

〔Effect of the invention〕

As described above, according to the present invention, in a camera having a passive AF system in which an image sensor also serves as a distance measurement sensor, a filter operating device that retracts an infrared cut filter installed in a camera optical path out of the optical path. Therefore, when the subject brightness is normal, the infrared cut filter is placed in the optical path of the camera, and when the subject brightness is below the low brightness limit, the filter operating device moves the infrared cut filter out of the optical path. It can be evacuated.

Therefore, distance measurement can be performed even under conditions where the brightness of the subject is low, such as during night photography, and AF photography becomes possible.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram showing an example of the present invention, and Fig. 2 (
a) and (b) are explanatory diagrams of the operation of the infrared cut filter of FIG. 1; 1...Imaging lens 2...Total reflection mirror 3...
- Infrared cut filter 4...Crystal plate 5...Image sensor 6...Half mirror 7...Penta prism 8...Finder lens 9...Photometric sensor 10...Solenoid 1
1...Spring 12...Center shaft

Claims (1)

[Scope of Claims] 1. A camera having a passive AF system in which the image sensor also serves as a distance measuring sensor, comprising a filter operating device for retracting an infrared cut filter installed in the camera optical path out of the optical path, An AF camera characterized in that when the output of a photometric element installed inside the camera is below the low brightness limit of the AF system, distance measurement is performed by retracting the infrared cut filter out of the optical path. 2. The AF camera according to claim 1, wherein the filter operating device for retracting the infrared cut filter installed in the camera optical path out of the optical path comprises a solenoid operated by an output from a photometric element installed inside the camera. 3. A according to claim 2, further comprising a spring that returns the infrared cut filter that has been evacuated out of the camera optical path into the camera optical path.
F camera.