JPS5841487B2 - focus detection device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is a device that automatically adjusts the focus of an optical system by detecting the sharpness of an object image. This invention relates to a detection device.

2. Description of the Related Art Various methods and devices have been proposed in the past for adjusting the focus of optical instruments by photoelectrically detecting changes in the sharpness of images of objects.

In this method, a photoelectric element detects changes in the amount of light when an image of an object formed by a photographing optical system is dynamically scanned at the imaging position using a mechanical means such as a slit. The method of detecting the sharpness of the image by analyzing the frequency of the output of the photodetector is also considered to be theoretically more accurate.

However, if such a method is adopted to construct an object image sharpness detection device, the device will become complicated and large, and many problems remain that must be solved, especially if it is used in small optical equipment such as cameras. has been done.

Furthermore, the above-mentioned types of devices, that is, the types of devices that photoelectrically detect the sharpness of an object image and adjust the focus of an optical system, each have different configurations, functions, and effects, but the principles are different. Specifically, by converting the illuminance distribution on the image plane of the object image due to the luminous flux from the object into an electrical signal using a photoelectric element and processing this appropriately, information corresponding to the sharpness of the object image can be obtained. The output is obtained and used as a control signal during focus adjustment, but with these conventional methods, the size of the light receiving element is inappropriate, making it difficult to obtain highly accurate detection results. It has the disadvantage that it is extremely difficult to constantly adjust the focus of the optical system well.

The present invention has been made in view of the above-mentioned circumstances, and in particular, scans the height of an object formed by an optical system and processes the scanning signal to obtain sharpness information of the projected image. ,
As a device that detects the focus based on this, it guarantees the formation of high-precision sharpness information at all times according to the screen size to be obtained on the planned imaging plane, and thus the device detects the focus. The object is to provide a focus detection device with improved performance and accuracy.

The present invention will be described in detail below with reference to the drawings.

FIG. 1 is a block diagram of an embodiment in which the device of the present invention is applied to a photographing optical system of an optical device such as a camera.

In FIG. 1, numeral 1 indicates an object such as a person whose sharpness is to be detected.

Reference numeral 2 denotes an optical system that is provided to form an image of the object and is movable along an arrow in the optical axis direction by a driving means (not shown).

3 is a photoelectric conversion means consisting of a large number of independent photoelectric element portions aligned in the vicinity of the image forming plane of the optical system 2;
Its detailed configuration will be explained with reference to FIG.

As is clear from the configuration described above, the image of the object 1 is formed on the photosensitive surface of the photoelectric conversion means 3 via the optical system 2, and the illuminance at each point of the nuclear body is converted into an electrical signal by each photoelectric element. be done.

Furthermore, as the optical system 2 moves in the optical axis direction, the sharpness of the object image on the photoelectric conversion means 3 changes, and the resulting changes in the illuminance distribution of the image are momentarily detected as electrical signals by the photoelectric element. Ru.

Reference numeral 4 denotes a time-series means, such as a ring counter, for taking out the photoelectric analog outputs of the large number of photoelectric element portions obtained in this way in a predetermined order.

A specific example of the time-sequencing means will be explained using FIG. 3.

Since the object image illumination on the photosensitive surface of the photoelectric conversion means is generally extremely low, such as 101 ux or less, each analog signal corresponding to the output of each photoelectric element portion from the time series forming means is Each analog signal corresponding to the output of each photoelectric element is extremely weak.

Therefore, in this proposal, this signal is amplified to an appropriate level via an amplifier 5, and then each amplified analog signal is input to an analog-to-digital conversion circuit 6, and after being converted into a digital signal, a small electronic is input into the calculator 7,
It is converted into an electrical output corresponding to the object image sharpness, that is, sharpness information.

The small electronic computer 7 is provided with programming that allows calculation of a function for evaluating object image clarity, which will be described in detail later.

Therefore, a digital human input signal is sent to the small electronic computer 7,
That is, when an input signal with a number of pulses corresponding to the illuminance of each point of the object image is input, calculations are performed moment by moment, and visibility information corresponding to the adjustment state of the optical system 2 at that time is sent to the computer 7.
This is something that can be obtained more easily.

The function for evaluating object image clarity as described above will be referred to as an evaluation function hereinafter.

The evaluation function is schematically shown in block 8 indicated by a broken line in FIG.

Since the output of the small computer 7 is a digital signal,
In order to facilitate subsequent processing, sharpness information is converted into an analog signal by the digital-to-analog conversion circuit 9, and is used to obtain an output for focus adjustment of a photographing optical system, etc. based on the sharpness information. The signal from the digital-to-analog conversion circuit 9 is input to a processing circuit 10, where the signal is converted into a signal output that can be supplied to a servo motor 12 for driving and controlling a display means 11 or a photographing optical system 13.

Needless to say, the display means receiving this signal input displays the object image sharpness or object distance using a known method, and the servo motor 12 can automatically adjust the focus of the photographing optical system 13. It is.

Further, the optical system 2 can be controlled by the servo motor 12 either alone or in conjunction with the photographing optical system 13.

The broken line in the figure schematically represents such a configuration.

In this embodiment, after the information processing process described above,
It detects the object image sharpness with extremely high sensitivity and makes it possible to adjust the focus of the photographing optical system based on the obtained sharpness information, but in particular, much of the information processing process is performed using digital signals. As is well known in information theory, the amount of information lost due to noise during that time is extremely small compared to analog processing, which is why it is always a difficult technique to process electrical output obtained from low-light object images. It becomes possible to sufficiently overcome the problem of signal-to-noise ratio, which appears as a barrier to performance.

Here, as the evaluation function calculated by the small electronic computer 7, the electric signal from each photoelectric element of the photoelectric conversion means 3 is Pi(
i=1, 2..., n: n is the number of the photoelectric elements)
In this case, for example, F given by the following equation may be selected, but it is not limited to the function of this example.

The above formula gives the square mean of the illuminance of each photoelectric element,
When the sharpness of the object image is low, the difference in brightness of the image is small, so Pi-P is small; when the sharpness is high, the difference in brightness of the image is large, so the value of Pi-P becomes large, and therefore F increases as the clarity improves.

FIG. 2 is a diagram showing the form of a large number of photoelectric element portions arranged in an array suitable for use in the device shown in FIG.
1 is a schematic configuration example of a photoelectric conversion means 3 in which photoelectric element portions 14 each having a minute area are arranged vertically and horizontally.
(abbreviated as U).

Of course, the shape of the photoelectric element portion 14 and the arrangement thereof are not limited to this example, and may be circular or the like.

Figures 2 and 2 are electrical connection diagrams of each element when a photoconductive element, a first diode, and a solar cell are used as the photoelectric element portion 14, and these are connected with one pole in common, The other pole is left open so that the individual outputs can be detected.

Furthermore, although not shown in this example, the above-mentioned CC is used as a photoelectric conversion means.
It is of course more possible than using I).

FIG. 3 is a block diagram showing one embodiment of the above-mentioned time-series forming means 4, and includes an oscillator 15 and a driver 16 for oscillating signals of appropriate frequencies for each photoelectric element constituting the photoelectric conversion means 3.
, and a ring counter 17 and transistors connected between each output terminal of the counter 17 and each of the photoelectric elements, and sequentially output analog outputs of the respective photoelectric elements connected to the selected transistors. end 18
It can be taken out from the circuit to the next stage circuit (not shown).

FIG. 4 is an explanatory diagram showing the image formation state by the optical system 2 and the photographing optical system 13 for determining the size of the photoelectric element of the present invention, and a diagram showing the image formation state on the photoelectric conversion means 3, Hereinafter, improvements in the present invention will be described in detail with reference to the same figure.

In FIGS. 4a and 4, 1 is an object, and for the sake of simplicity, it is assumed that it is a circle with an area of S.

The object image is focused on the photoelectric conversion means 3 and the film surface 20 by the optical system 2 having a focal length f and the photographing optical system 13 having a focal length f%, as shown in FIGS. 4a and 4, respectively. imaged.

If the distances from the object 1 to the front focal points of the optical systems 2 and 13 are both X, then the area S1 of the object image 1' on the photoelectric conversion means 3 when the focus is correctly adjusted is: The area S2 of the object image 1'' is .

From equations (1) and (2), in equation (3), S2
Assuming that is equal to the area of the circle of least confusion, the film plane 20
The area of the circle of minimum confusion on the photoelectric conversion means 3 when the object image clarity is maximum in the above is equal to 81 in (3).

This situation is shown in FIG. 4C.

FIG. 4d shows a state in which the object image 1' has become unclear. At this time, in order for the photoelectric output of each photoelectric element 14 to change sharply in accordance with the sharpness, As shown in FIG. 4C, the area S1 of the circle of least confusion must be approximately equal to or less than the area φ of the light receiving portion of each photoelectric element.

By setting the size of the photoelectric element in this way, even if the sharpness of the object image slightly decreases from its maximum value, it will affect the surrounding photoelectric elements and detection will become possible.

In general, the circle of least confusion is determined according to the area F of the screen size set on the planned imaging plane of the film, etc., but since there is no established chart, for convenience, ms2 = F (m is a positive number) (4), then it is sufficient if the above and equations (3) and (4) are satisfied.

In reality, m<900000 (6) when considering the area of the screen size (36ii x 24im) and the area of the circle of least confusion in a normal 35-inch film camera.

When the photoelectric conversion means 3 itself is used as a means for detecting image information of an object, or when the optical system 2 is used together as a photographing optical system, if f=f' in equation (5), then The area φ of each photoelectric element is determined.

As detailed above, according to the present invention, the area of the light receiving part of the photoelectric conversion element included in the photoelectric conversion means as the image scanning means is adjusted according to the area of the screen size to be obtained on the planned image forming plane. By setting this, it is possible to always detect highly accurate image clarity according to the screen size, and therefore, the detection performance and detection accuracy of the focus detection device can be significantly improved. be.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment in which the device of the present invention is applied to a photographing optical system of an optical device such as a camera, and FIG. An explanatory diagram for explaining the configuration of the photoelectric conversion means, FIG. 3 is a block diagram of an embodiment of the time-series means shown in FIG. 1, FIG. FIG. 1 is an explanatory diagram showing the imaging state of an object image generated by the device shown in FIG. 2... Focus detection optical system, 3... Photoelectric conversion means, 1
4... Photoelectric conversion element, 4... Signal time series generation means, 5
゜6.7, 8, 9... Components of signal processing means, 10
... Focus detection means, 12 ... Servo motor, 13
...Main optical system.

Claims (1)

[Scope of Claims] 1. When a detected image of an object is formed and the relationship with the first reference plane is set so that the detected image is aligned with the first reference plane, the focus on the object is set. a focus detection optical system that determines the relationship between the main optical system to be matched and a second reference plane relative to the main optical system so that the object image formed by the refined optical system matches the second reference plane; A photoelectric conversion means including a plurality of photoelectric conversion elements for scanning the detected image on a predetermined scanning plane, and a photoelectric conversion means for scanning the detected image on the scanning plane by processing a scanning signal from the photoelectric conversion means. and a focus detection means for detecting alignment or misalignment of the detected image with respect to the first reference plane based on the sharpness information; The focal length of the focus detection optical system is f1, the focal length of the main optical system is f', the area of the screen size set on the second reference plane is Fl, or m is a positive number of m≦9X10'. Then, regarding the area φ of the light receiving part of the photoelectric conversion element, φ
A focus detection device that satisfies ≦(f/fl)2·F 7m. 2. An imaging optical system that is adjusted to form an image of an object on a predetermined reference plane, and a photoelectric conversion device that includes a plurality of photoelectric conversion elements for scanning the object image on a predetermined scanning plane. a signal processing means for outputting sharpness information of the object image on the scanning plane by processing the scanning signal from the photoelectric conversion means; and a focus detection means for detecting the adjustment state, and when the area of the screen size set on the reference plane is Fl, and m is a positive number of m≦9×105, the light receiving portion of the photoelectric conversion element is provided. A focus detection device characterized in that the area φ satisfies φ≦F/m.