JPH0442207A - Autofocusing device - Google Patents

Abstract

PURPOSE:To shorten the detecting time of a focal position by detecting the focal position based on plural images image-formed on an image-forming plane by a small lens group optical system, and moving a focusing lens to the focal position by retreating the small lens group optical system from the optical path of a photographic optical system when photographing is performed. CONSTITUTION:A photographic lens system 1 consists of lens systems 1 and 3, and a lens array (small lens group optical system) 2 is arranged in the optical path of the photographic optical system in such a way that it can be inserted. The small lens group optical system 2 is located at the position of the optical path where the almost analogous or analogous partial image of an object image by only the photographic optical system can be formed when it is inserted to the optical path, and the focal position can be detected by the plural images image-formed on the image-forming plane by the small lens group optical system 2. The small lens group optical system 2 is retreated from the optical path of the photographic optical system when the photographing is performed, and the focusing lens is moved to the focal position. Thereby, it is possible to shorten the detecting time of the focal position.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention is an autofocus device suitable as a focusing device for an electronic still video camera. The present invention relates to an autofocus device that takes into account.

(Prior art) Focusing operations in video cameras, electronic still cameras, etc. extract the high frequency components of the video signal of the subject image taken in from the photographing lens system, process it in a control circuit, and drive the lens by a search control system. is common.

A typical example of this control method is the mountain climbing servo method.

The hill-climbing servo method is to drive the lens to determine whether it is toward infinity or close range, and then move the lens in the determined direction to reach the peak of the mountain that is the in-focus position (the high-frequency component of the brightness signal). It is a servo control force type that determines the peak of the mountain by heading toward the maximum value (maximum value) and passing the peak of the mountain, and brings the lens to the focusing position.

(Problem to be solved by the invention) As is clear from the above operation, this mountain climbing control method processes the luminance signal multiple times before detecting the in-focus position, and drives the lens many times during the processing process. Ta. Furthermore, since the above-described process takes place, it takes time to complete the detection of the in-focus position, which often results in erroneous distance measurements.

This mountain-climbing method can be applied to electronic still cameras, but unlike video cameras, which require constant focus while shooting, electronic still cameras have the advantage that they only need to be in focus while shooting. It has the following.

Therefore, there is no necessity for an electronic still camera to adopt an autofocus device similar to the above-mentioned mountain climbing servo system.

However, in order to detect the peak of the high-frequency component of the video signal and determine the focus point, it is necessary to move the lens from close range to infinity, which is disclosed in Japanese Patent Application Laid-Open No. 63-217.
No. 879 discloses an electronic still camera configured in this manner.

Therefore, in this case as well, there is a drawback that it takes time to measure the distance.

The purpose of the present invention is to detect the focus position by bringing the focus lens to a predetermined position in advance, inserting the lens array into the optical path of the photographing optical system, and capturing one image. An object of the present invention is to provide an autofocus device that can shorten the time required for autofocusing.

(Means for Solving the Problems) In order to achieve the above object, an autofocus device according to the present invention includes a small lens group optical system having a plurality of small lenses arranged in one plane in the optical path of a photographing optical system. can be inserted into
Each of the small lenses has a different focal length such that when the focus lens is at a specified position, the image formation state on the imaging surface is the same at each position of the focus lens from infinity to close range, and the small lens group optical The system is at an optical path position such that when the small lens group optical system is inserted into the optical path, a substantially similar image of the subject image or a partial image of the similar image by only the photographing optical system is focused on the imaging plane, and the small lens group optical system A focusing position is detected by a plurality of images formed on an imaging surface by the system, and when photographing, the small lens group optical system is retracted from the optical path of the photographing optical system and the focus lens is moved to the focal position. It is composed of:

(Example) Hereinafter, the present invention will be explained in more detail with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of an autofocus device according to the present invention.

The photographic lens system is composed of lens systems 1 and 3. A lens array (small lens group optical system) 2 is arranged so as to be insertable into the optical path of this photographing lens system. An image of a subject (not shown) is formed on the CCD 4. The output of the CCD 4 is input to the video signal circuit 5, and the video signal circuit 5 is connected to the COD
It processes the output, adds a synchronization signal, etc., and outputs a video signal.

The video signal circuit 5 also outputs a luminance signal and inputs it to the focus detection circuit 6.

When the lens array 2 is inserted into the optical path, the focus detection circuit 6 extracts the high frequency components of the luminance signal for each part of the screen (split screen) that each small lens forms an image on, and calculates the high frequency components for all the split screens. Compare output levels.

The control circuit 7 determines that the position of the focus lens corresponding to the maximum level divided screen is the in-focus position. Furthermore, if the maximum level cannot be determined (if the in-focus position is between each position of the focus lens from the closest to infinity), a correction process is performed to calculate the focus lens position.

Then, based on the above information, the focus lens is controlled to be brought to the in-focus position. In addition, lens array 2
Controls the insertion and withdrawal of the lens into the photographic lens system.

The ON information of the release button 8 is input to the control circuit 7.

FIG. 2 is a perspective view showing details of the lens array.

In this embodiment, the lens array 2 is constructed by arranging nine small lenses, and when the focus lens is fixed at a specified position, the number of images formed on the CCD d by each small lens is nine. This is an image of a subject that is similar in shape to the image created by bringing the focus lens to each predetermined position between infinity and close range.

For example, the small lens 2-1 at the upper left end position of the lens array 2
When photographing, the same image (with the same amount of blur) with the focus lens placed at the infinite position is formed at the corresponding position on the CCDd.

Furthermore, the small lens 2-2 forms an image that is slightly closer than the infinite end when the focus lens is brought closer.

The small lens 2-n at the lower right end position forms an image equivalent to that produced at a close position.

In this way, the lens array 2 forms a plurality of images (positions corresponding to each small lens on the CCDd) whose focus positions gradually differ from the infinite position to the close position.

FIG. 3 is a diagram showing the degree of focus of an image with respect to a scene including a mountain at a position equivalent to infinity, a tree at a middle distance, and a person at a close position.

The upper left area of the CCD, which forms an image of a subject at an infinite position, contains a focused image of a distant mountain, and the central area of the COD, which forms an image of a subject at a medium distance, contains a focused image of a tree. However, a focused image of a person is formed in the lower right area of the CCD, which forms an image of a nearby subject.

FIG. 4 is a diagram showing details of the imaging optical system.

Lens system 1 is a variable magnification lens system 12, lens system 3 is a mask lens system 10, a lens array 2 is inserted between them, and an aperture 9 is arranged between the lens array 2 and the variable magnification lens system 12.

Next, the operation of FIG. 1 will be explained with reference to FIGS. 5 and 6.

The center of the field of view of the finder is the focus area.

When not photographing, the focus lens is brought to a specified position, and the lens array 2 is also inserted into the optical path of the photographic lens system.

When the release button 8 is pressed and turned on, an image of the subject formed on the CCDs 4 , .

The focus detection circuit 6 extracts the luminance signals corresponding to the positions of each portion of the screen (nine divided screens) imaged by the nine small lenses, and extracts their high frequency components. Then, the magnitude of the high frequency component of the luminance signal of each divided screen is compared, and the comparison result is transmitted to the control circuit 7.

For example, if the subject exists between an infinite position and a close distance, each divided area a% defined in Figure 5(a)
The focus signal level of i is a signal as shown in FIG. 5(b), and in such a case, the focus detection circuit 6 outputs a comparison result indicating that the focus signal level of divided area e is the maximum.

When the control circuit 7 obtains information about the area where the focus signal level is maximum from the focus detection circuit 6, it retracts the lens array 2 from the optical path of the photographic lens system and moves the focus lens to the focus lens position corresponding to that area. drive

A focusing operation is performed in this manner.

After focusing, the video signal output from the video signal circuit 5 is stored in a storage medium (not shown).

When photographing is completed, the control circuit 7 inserts the lens array 2 into the optical path and performs control to bring the focus lens to a specified position.

It should be noted that the lens array 2 can be configured such that it is normally retracted from the optical path and is inserted into the optical path when the release button is pressed halfway, for example.

FIG. 6 shows an example of the focus signal level when the subject exists between the focus lens positions associated with each divided area.

When the peak of the mountain formed by connecting the focal signal levels of each divided area does not match the focal signal level of a specific area, that is, when there is almost no difference between the focal signal levels corresponding to the divided areas before and after the peak of the mountain. , the control circuit 7 performs correction according to the degree of the difference.

If the difference is greater than a predetermined value (determined from the comparison output of the focus detection circuit), it can be determined that the focus signal level corresponding to that area matches the top of the mountain as described above, but if it is less than the predetermined value, the difference is Calculate the corrected distance to the summit based on the information.

Therefore, for example, in the case of Fig. 6, the focus lens position is the focus lens position corresponding to the divided area d plus the correction value (corresponding to the area d'' which is not actually set between the divided areas d and e). Focus lenses will be introduced.

It should be noted that there may be cases where it is difficult to form images clearly into each divided area near the boundaries of the small lenses, so in such cases, focus signal data should be extracted only for the necessary area of each divided area. Good too.

(Effects of the Invention) As explained above, the present invention inserts the small lens group optical system into the optical path of the photographing optical system with the focus lens brought to the specified position, and each small lens is used to adjust the distance between the object from infinity to close range. The focal length is set so that the subject is in focus at each position, and by comparing the high frequency components of the video signal of the screen portion that each small lens forms, the subject can be focused at each position from infinity to close range. It is configured to detect the focus lens position to be achieved at a certain time.

Therefore, according to the present invention, since the in-focus position can be detected by capturing only one screen, the time required for distance measurement can be reduced.

Further, since the configuration is such that a small lens group optical system is inserted into the photographic lens system and the image pickup element of the photographic lens system is used as is, there is an advantage that another image pickup element for distance measurement, etc. is unnecessary.

[Brief explanation of the drawing]

FIG. 1 is a schematic block diagram showing an embodiment of an autofocus device according to the present invention, FIG. 2 is a perspective view showing details of a lens array, FIG. 3 is a diagram showing an example of an image formed on a finder, and FIG. Figure 4 is a schematic diagram for explaining the details of the photographing optical system, Figure 5 is a diagram showing the signal level of high frequency components extracted from each split screen when the subject is located between an infinite position and a close distance. FIG. 6 is a diagram showing an example of correction when the position of the subject is between positions corresponding to each area. 1.3... Lens system 2... Lens array (small lens group optical system) 4...
Image pickup device (CCD) 5...Video signal circuit 6...Focus detection circuit 7...Control circuit 8...Release button 9...Aperture 10...Mask lens system 11...Lens array 12 ...Variable power lens system 14...Subject Patent applicant: Kyocera Co., Ltd. Agent: Patent attorney Hisashi Inoro b)

Claims (1)

[Claims] A small lens group optical system consisting of a plurality of small lenses arranged in one plane can be inserted into the optical path of the photographing optical system, and each of the small lenses can be inserted into the optical path of the focus lens from infinity to close range when the focus lens is at a specified position. The focal lengths are different so that the image formation state on the imaging plane at each position is the same, and the small lens group optical system is controlled only by the photographing optical system when the small lens group optical system is inserted into the optical path. The optical path position is such that a substantially similar shape of the subject image or a partial image of the similar shape is focused on the imaging surface, and the in-focus position is detected by a plurality of images formed on the imaging surface by the small lens group optical system, An autofocus device configured to move the focus lens to an in-focus position by retracting the small lens group optical system from the optical path of the photographing optical system during photographing.