JPH0894924A - Focus detector - Google Patents

Abstract

PURPOSE: To obtain a focus detector whose responsiveness until a focusing state is attained is quick and which need not be provided with a complicated optical system by discriminating an out-of-focus direction by comparing out-of-focus quantity with the out-of-focus quantity obtained when the focusing action of a photographing lens system is changed. CONSTITUTION: The focus detector is provided with a correlation arithmetic operation means 8 constituted so that the photographing lens system 1, an image pickup element 5 and a light splitting means 7 splitting luminous flux transmitted through the lens system 1 into plural areas are arranged in an optical path and the out-of-focus quantity on the element 5 is obtained by extracting the characteristics of plural images simultaneously formed on the element 5 and a comparison arithmetic operation means 9 comparing the out-of-focus quantity obtained when a part or the whole part of the lens system 1 is moved on an optical axis thereafter and discriminating the out-of-focus direction. Then, when the element 5 is used as a sensor for range-finding, an area 6 used when the image is fetched may be different from the original image pickup area. Besides, the area 6 may be varied while a focus is detected. Therefore, the constitution of the detector is simplified by using the element 5 in common with the range-finding sensor. Besides, an out-of-focus detecting action and a focusing action satisfying the high-speed responsiveness necessary for a still image are executed.

Description

Detailed Description of the Invention

[0001]

The present invention relates to an electronic still camera, etc.
The present invention relates to an automatic focus adjustment device suitable for still image shooting, and more particularly to an automatic adjustment device that also uses a group image pickup device or the like as an image pickup device as a distance measuring sensor.

[0002]

2. Description of the Related Art Conventionally, two types of TTL-type automatic focus adjustment methods are known, that is, a method for detecting a blur on a surface corresponding to a focus and a method for detecting a shift.

A typical example of the former is a focus adjusting device using an image pickup signal of a video camera using a solid-state image pickup device as a photoconductor, and the latter is a secondary optical system of a secondary image forming type of a silver salt still camera. It is a shift detection focus adjustment device equipped with each, and each has its own features.

As shown in FIG. 2, the former focus adjusting device utilizing an image pickup signal basically comprises a variable power optical system 21 having a variable power lens group 22 and a focus lens group 23, and a photoconductor 24. The in-focus state is determined from the sharpness of the subject image that passes through the variable power optical system 21 and is formed on the photoconductor 24. In a video camera or the like, the photoconductor 24 is a photoelectric conversion element such as a solid-state image pickup device, and as a well known method, a high frequency component of an image pickup signal obtained from the photoconductor 24 at the time of focusing becomes high. Is used to control the position of the focus lens group 23. Therefore, at the time of non-focusing, it is necessary to slightly vibrate the focus lens group 23 back and forth to detect the direction of focusing and the non-focusing state.

However, in the above-mentioned conventional example, the defocus amount at the time of non-focusing is not uniquely obtained although the configuration is simple, so that the response to focusing is slow, and the time lag is particularly important for stillness. Not suitable for photography.

On the other hand, as shown in FIG. 3, the structure of the shift detection focus adjusting device is such that the focus detecting device is located between the variable power optical system 31 having the variable power lens group 32 and the focus lens group 33 and the photosensitive surface 34. A polarizing means 36 for branching the light flux to 35 is arranged, and in the vicinity of the primary image forming surface 37 corresponding to the photosensitive surface 34, a focus lens 38, a field mask 39, separator lenses 40a and 40b, a distance measuring sensor 41a, 41b is arranged. The field lens 38, the field mask 39, and the separators 40a and 40b are for taking in the light fluxes from different regions passing through the variable power optical system, and the light fluxes are received by the distance measuring sensors 41a and 41b, Part 2
Compare the correlations of the images and find the deviation. When focusing, the same two images are formed on the distance measuring sensors 41a and 41b, and in the non-focusing state, the two images are horizontally shifted depending on the degree of defocus. By calculating the defocus amount and the direction on the image surface from the amount of the lateral displacement and converting the defocus amount and the direction into the extension amount of the focus lens group 33, so-called prediction can be achieved in which the focus state is immediately reached. The greatest advantage of the shift detection focus adjustment device is the high-speed response due to this prediction, and it can be said that it is suitable for still image shooting.

However, in the above-mentioned conventional example, it is necessary to retract the deflecting means 36 for branching the light beam to the focus detecting device 35 to the outside of the effective light beam for photographing at the time of photographing, and the secondary image forming optics for detecting other principal points. It is unavoidable that the configuration including the system becomes complicated.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above problems, and to provide a focus detection device which has a fast response until focusing and does not have a complicated optical system.

[0009]

According to the present invention, a taking lens system, an image pickup device, and a light splitting means for dividing a light flux passing through the taking lens system into a plurality of regions are arranged in an optical path, and the light pickup device is provided on the image pickup device. Correlation calculating means for obtaining the amount of focus shift on the image pickup device from the feature depiction of the plurality of images formed at the same time, and the amount of focus shift obtained when the part or the whole of the taking lens system is subsequently moved on the optical axis. The present invention proposes an automatic focus adjusting device having a simple structure and suitable for still image shooting by comparing the values with the comparison calculation means and determining the direction.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS For a more detailed understanding of the present invention, an explanation will be given according to the flow charts of FIGS. 1 and 5 which are embodiments of the present invention.

In FIG. 1, reference numeral 1 denotes a variable magnification photographing lens system including a variable magnification lens group 2 and a focus lens group 3.
A diaphragm 5 is an image pickup device for picking up a subject image formed by the taking lens system 1. When the image pickup device 5 is used as a distance measuring sensor, the area 6 at the time of capturing an image may be different from the original image pickup area,
It may be variable during focus detection.

In this embodiment, a light splitting means 7 (moving diaphragm plate or liquid crystal plate) for splitting a light beam into two images is arranged in the vicinity of the stop 4, and the existing light splitting means 7 has two openings 7a. And 7b are provided, but their positions need not be limited here.

Now, the openings 7a and 7b are arranged along the horizontal scanning line direction of the image pickup element 5, but if the directions for obtaining the correlation of the images match this, they are in the vertical direction. However, in some cases, instead of two images, a total of four images vertically and horizontally,
Alternatively, a large number of apertures may be used so as to capture a plurality of images larger than that.

The openings 7a and 7b are arranged substantially symmetrically with respect to the optical axis, and the distance between the centers of gravity of the respective openings corresponds to the conventional baseline length. Therefore, the farther the opening is, the longer the baseline length is, and the detection accuracy is improved. On the other hand, when the image is greatly out of focus, the separation width of the two images on the image sensor 5 may become too large, and the correlation may not be obtained.
It is necessary to appropriately set the detection area 6 by increasing the size or reducing the baseline length.

After the focus adjustment is completed, the light splitting means 7 is retracted to the outside of the optical path at the time of photographing, or the light splitting means 7 is composed of a physical property element such as liquid crystal or electrochromy, and its position is fixed. As it is, the light quantity may be transmitted or non-transmitted by electrical on / off.

Correlation calculation means 8 is means for drawing out the characteristics of the image from the two images obtained at the same time and obtaining the amount of separation.

Now, the area 2 is blurred in the horizontal scanning line direction.
When the image [dotted line in FIG. 4 (A)] is formed, the combined signal [FIG.
Based on (A) solid line], the separation width of the two images is obtained. Now, a difference is taken for each pixel of the composite signal [FIG. 4 (B)], and a differential signal [FIG. 4 (C)] which is the difference is considered.

The differential signal is gradually shifted to obtain the autocorrelation, and this is obtained as a single evaluation amount, as shown in FIG. 4 (D). FIG. 4D shows the autocorrelation amount shifted to only one side, and Δ in the figure is the separation amount of the two images to be obtained.

From the image separation amount thus obtained, it is possible to determine the amount of movement of the focus lens group 3 of the photographing lens system 1 required for focusing by calculation, with the payout sensitivity of the focus lens group 3 being known, but with this alone. The so-called front pin and rear pin cannot be judged. Because the openings 7a, 7
This is because the two images that have passed through b are reversed between the front focus and the rear focus, and it is not possible to specify which aperture image is formed.

In order to solve this, in this embodiment, after the focus shift is obtained once, a part or the whole of the taking lens system is moved by a small amount on the optical axis, the focus shift is obtained again, and the comparison is made. The calculation means 9 calculates the difference from the previous one.

The moving lens group is the focus lens group 3
However, it is not limited to this, and the entire system may be moved.

If the difference in the amount of defocus is decreasing, the focus lens group 3 may be moved in the same direction as this time by a predetermined amount, and if the difference in the amount of defocus is increasing, it may be moved in the opposite direction. . Further, if the initial movement amount of the focus lens group 3 when obtaining the difference is known, the payout sensitivity of the focus lens group 3 can also be known, and it is not necessary to know it.

In the flowchart of FIG. 5, the switch SW1 is turned on by, for example, half-pressing a release button (not shown). Then, the light splitting means is inserted into the optical path to start the distance measurement, or a light shielding plate having two openings is formed by liquid crystal or the like (step 51). Next, in step 52, a correlation calculation is performed, and the calculated shift amount is determined in step 53 as the depth width 53.
Compared to. If the deviation amount is included in the depth range, the determination is YES and the distance measurement is completed (step 5
4). On the other hand, when the shift amount is not included in the depth width, the constant drive of the focus lens is instructed (step 55), the focus lens is driven (step 56), the signal is read again, and the correlation calculation (step 52) is performed to perform the shift. Find the amount. If the deviation amount is within the depth width in step 53, the distance measurement is completed (step 54), but if it is outside the depth width, it is compared with the previous deviation amount in step 51, and the deviation direction is determined in step 58. Then, the focus lens is driven so as to cancel the predetermined shift amount in the obtained shift direction (step 5
6) Then, the distance measurement is completed. Then, when the release button is further pressed to turn on the SW2, the light splitting means is retracted (step 59), the object image is captured and stored (step 60), and the read signal is recorded (step 61). To be done.

With such a configuration, it is possible to determine the direction of the focus shift necessary for the prediction and to determine the amount of extension of the focus lens group 3 for correcting it, by performing the above operation only once.

Further, the payout sensitivity when the out-of-focus state is large is slightly different from that near the in-focus state, and the desired in-focus precision may not be obtained by only one prediction due to various other conditions. In that case, this operation may be repeated.

Further, only the first prediction is performed by this method, and when the vicinity of the in-focus is reached, switching to the conventional focus adjustment method using the image pickup signal can contribute to shortening the response time.

[0027]

As described above, according to the present invention,
By using the image pickup device for the original image pickup as the distance measuring sensor, the structure can be simplified, and the shift detection focus adjustment satisfying the high-speed response required for a still image can be performed.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of the present invention.

FIG. 2 is an optical layout diagram of a conventional example.

FIG. 3 is an optical layout diagram of a conventional example.

FIG. 4 is a diagram showing an output signal.

FIG. 5 is a flowchart of deviation detection.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Magnification photographing lens system 2 Magnification lens group 3 Focus lens group 4 Aperture 5 Image sensor 7 Light splitting means 8 Correlation calculation means 9 Comparison calculation means

Claims (3)

[Claims] 1. A signal from an image pickup device for receiving an image by a photographing lens system, a dividing means for dividing a light flux passing through the photographing lens system into a plurality of light fluxes, and a signal from the image pickup element for simultaneously capturing a plurality of images by the dividing means. Correlation calculation means for obtaining the amount of defocus on the image sensor surface from the correlation of the image and the amount of defocus in that state and the amount of defocus when the focus adjustment of the photographic lens system is changed are compared. A focus detection apparatus comprising: a comparison calculation unit that determines a direction. 2. The focus detection device according to claim 1, wherein the dividing means is a light shielding member having an opening symmetrical with respect to the optical axis. 3. The focus detection device according to claim 1, wherein the focus adjustment of the taking lens system is performed by moving a part or all of the lens system in the optical axis direction.