JPS6162011A - Focus detector - Google Patents

Abstract

PURPOSE:To obtain a focus detector for detecting a focus accurately without the influence of temperature change by compensating defocusing variable on the basis of an output of a temperature detecting means. CONSTITUTION:The image of an object obtained from an image-forming optical device 1 is led into a photoelectric converter 2 and the focus of the device 1 is detected on the basis of an output from the converter 2. The titled detector is provided with a defocusing variable calculating means 3 for detecting the difference between the image forming surface of the device 1 and a prescribed detecting surface, i.e. a defocusing variable, from the output of the converter 2, a temperature detecting means 4 for generating an output corresponding to a temperature and a compensating means 5 for compensating the calculated contents or output of the means 3 on the basis of the output of the temperature detecting means. The compensating means 3 calculates the changed value of the defocusing variable due to temperature change from the output of the temperature detecting means 4 and sends the calculated value to the means 3 to compensate its calculated contents or compensates the output of the means 3 by the changed value.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention is directed to guiding an object image from an imaging optical device such as a camera onto a photoelectric conversion device, and converting the output of the photoelectric conversion device to the focal point of the imaging optical device. The present invention relates to a focus detection device that performs detection.

(Background of the Invention) Conventional focus detection devices include, for example, those shown in FIGS.
There is something like the one shown in the figure.

That is, the focus detection device is located behind a predetermined detection surface 6a provided at a position approximately optically equivalent to the film surface 11 of the camera, and the light beam that has passed through the photographing lens 12 is transmitted through the quick return mirror 13. , the optical path is bent downward by the sub-mirror 14 and reaches a predetermined detection surface 6a.

The focus detection device includes a focus detection optical device 7 that re-images the primary image of the photographing lens 12 formed on a predetermined detection surface 6a;
The photoelectric conversion device 2 provided at the image forming position of the focus detection optical device 7 and the image output obtained from the photoelectric conversion device 2 are processed to determine the difference between the image forming surface of the photographing lens 12 and the predetermined detection surface 6a, That is, it is comprised of an arithmetic device 3o that calculates the amount of defocus, and a drive display device 9 that performs drive display based on this amount of defocus.

As shown in FIG. 6, the focus detection optical device 7 includes a pair of photoelectric conversion element arrays 210, 220-1 included in the photoelectric conversion device 2, which re-image an aerial image on a predetermined detection surface 6a. It is constituted by re-imaging lenses 71 and 72, and the arithmetic unit 30 is a photoelectric conversion element array 21o.

The amount of relative shift of the optical image is detected from the image output of 220 to determine the amount of defocus.

However, such a conventional focus detection device has a problem in that when the temperature of the environment changes, the optical path length changes due to expansion and contraction of the constituent members, resulting in a focus detection error.

That is, in the conventional focus detection device, for example, if the position or inclination of the sub-mirror 14 changes due to thermal expansion of the mechanical support member, etc., and the optical path length between the film surface F and the predetermined detection surface 6a deviates by several tens of grams, the amount may directly become a focus detection error, or the re-imaging lens 71.
72 and the pair of photoelectric conversion element arrays 2] 0, 220 due to temperature changes, and especially when the re-imaging lenses 71 and 72 are made of plastic, such temperature changes may occur. There is a problem in that the amount of defocus is affected by temperature changes due to thermal expansion and changes in bending ratio, resulting in focus detection errors.

FIG. 7 shows another conventional example of the focus detection optical device 7,
This figure shows a reflection type re-imaging optical system disclosed in Japanese Patent Application Laid-Open No. 59-42507 by the present applicant.

This reflective re-imaging optical system consists of four transparent blocks 71
0,720,730,740, and the opening of the light shielding plate 750 provided on the predetermined detection surface 6a? The light flux from 51 is reflected by the reflective surface 721 on the bottom of the block 720, further reflected by the reflective surface 731 of the block 730, and directed to the concave mirrors 781, 782, and the concave mirror 781.7F32.
The reflected and deflected light flux passes through light transmitting parts 771 and 772 to form secondary images in secondary image plane detection areas 781 and 782.

However, even when such a reflective re-imaging optical system is used, if some of the blocks 710 to 740 are made of plastic or the like, the defocus amount will be affected by temperature changes, resulting in focus detection errors. There was a problem that this occurred.

(Objective of the Invention) The present invention has been made by focusing on such conventional problems, and an object of the present invention is to provide a focus detection device that can perform focus detection with high precision without being affected by temperature changes. The purpose is

(Summary of the Invention) In order to achieve the above object, in the present invention, as shown in FIG.
In a focus detection device that detects the focus of the imaging optical device 1 based on the output of the photoelectric conversion device 2, the difference between the imaging surface of the imaging optical device 1 and a predetermined detection surface, that is, the defocus a defocus amount calculation means 3 for detecting the amount from the output of the photoelectric conversion device 2; a temperature detection means 4 for emitting an output corresponding to the temperature; and a defocus amount calculation means 3 for detecting the amount from the output of the photoelectric conversion device 2; A correction means 5 for correcting the calculation content or output is provided, and the correction means 5 calculates the amount of change in the defocus amount due to temperature change from the output of the temperature detection means 4, and the amount of change is indicated by a broken line arrow. The output from the defocus amount calculating means 3 is sent to the defocus amount calculating means 3 and the calculated contents are corrected, or the output from the defocus amount calculating means 3 is corrected by the amount of change as shown by the solid line arrow.

(Example) Hereinafter, an example of the present invention will be described based on the drawings. Note that the same parts as in the conventional example are given the same reference numerals.

2 to 4 show an embodiment of the present invention.

As shown in FIG. 2, the focus detection optical device 6 of the focus detection device is disposed behind a predetermined detection surface 6a provided at a position approximately optically equivalent to the film surface 11 of the camera, and passes through the photographing lens 12. The light flux is the quick return mirror 13
The optical path is bent downward by the sub-mirror 14 and reaches a predetermined detection surface 6a.

Photography lens 12. Quick return mirror 13. The imaging optical device 1 is constituted by the sub-mirror 14 and the film surface 11.

An optical system as shown in FIG. 6 or 7 is used as the focus detection optical device 7 for re-imaging the primary image of the photographing lens 12 formed on the predetermined detection surface 6a.

In FIG. 2, 2 is a photoelectric conversion device, and a pair of CC
D-system image sensors (hereinafter simply referred to as image sensors) 21 and 22 are included.

The image sensors 21 and 22 are arranged on the imaging plane of the focus detection optical device 7, and a subject image is formed on each image sensor 21 and 22, respectively. Image sensor 21.2
A part of 2 is shielded from light and becomes an optical black part 21a.
, 22a are formed.

The image sensors 21 and 22 are connected to the data memory means 51 of the microprocessor 50 via the A/D converter 23, and the image outputs of the image sensors 21 and 22 are transferred in chronological order after a predetermined accumulation time. and A/D
The data is stored in the data memory means 51 of the microprocessor 50 via the converter 23.

Since the image sensors 21 and 22 have the above configuration, the outputs of the pixels corresponding to the optical black portions 21a and 22a reflect the magnitude of the dark current.

Outputs as shown in FIG. 3 are transferred from the image sensors 21 and 22. In FIG. 3, when the vertical axis is the output voltage and the horizontal axis is time, first an empty output 2A of a part of the shift sister (not shown) for transferring the image sensor output appears, and then the optical black portions 21a and 22a appear. output 2B appears, and finally the image sensor 2C appears. Therefore, the magnitude of the dark current is exactly the amount shown by Vd in FIG. 3, and is given as the difference between the output voltage of the output 2B of the optical black parts 21a and 22a and the output voltage of the output 2A of the shift register part.

Specifically, in order to obtain this Vd, it is possible to hold the output voltage of a part of the shift register 2A as a reference level during A/D conversion, or to hold the output voltage of a part of the shift register 2A. The potential may also be A/D converted and read, and the difference may be determined within the microprocessor 50.

In this embodiment, the optical black portion 21a.

22a functions as the temperature detection means 4, and the optical black parts 21a and 22a function as the second temperature detection means 4.
As shown in the figure, it is usually provided at one end of the image sensors 21 and 22, and the outputs of the optical black sections 21a and 22a are usually used as a black reference for the image output 2C.

As in this embodiment, the optical black portion 21a.

When trying to monitor the temperature from the output of 22a, if the accumulation time is long enough to make it possible to detect the amount of accumulated charge due to dark current at room temperature, the image output 2C will be saturated unless it is very dark. This causes problems such as blooming and smearing.

Regarding the influence of these surplus charges on the optical black parts 21a and 22a, when the outputs of the optical black parts 21a and 22a are output at the beginning of transfer, there is less influence on the optical black parts 21a and 22a than when they are sent out after image output. It is preferable to output the outputs of the sections 21a and 22a before the image output 2C.

However, if the optical black parts 21a and 22a are adjacent to the image output part, it is difficult to completely avoid the influence of excess charge, so it is preferable to insert dummy pixels between them, and furthermore, they are completely separated from the image sensor part. The optical black section 21a is located at the location where the optical black section 21a is located.

It is best if 22a is provided.

Further, in order to partially increase the sensitivity of the dark current monitor, the size of the pixels of the optical black portions 21a and 22a for the dark current monitor may be increased.

Further, as shown in FIG. 2, the microprocessor 5
0, in addition to the data memory means 51, there is a defocus amount calculation means 3. A correction means 5 and a control means 52 are provided.

The defocus amount calculation means 3 includes an image sensor 21.2.
The relative shift amount of the optical images formed on the image sensors 21 and 22 is detected from the image output 2C of 2.

The correction means 5 takes out a value corresponding to the voltage Vd corresponding to the dark current, that is, a dark current corresponding value Xd, from the memory section of the data memory means 51 containing data corresponding to the optical black parts 21a and 22a, and reads this value. The temperature t is calculated from the dark current corresponding value Xd by using the relationship that the dark current doubles for every r'C. here,
to is the reference temperature, for example 20°C, and XdO is 1=1
This is the value of Xd when it is 0.

Note that when determining the dark current corresponding value Xd, if the potential of the shift register section is not used as a reference, the dark current corresponding value Xd is determined by subtracting data corresponding to the output 2A of the shift register section.

Further, the correction means 5 calculates a defocus error ΔP due to temperature change from the temperature t.

ΔP = f (t), and since this functional form f (t) differs depending on the cause of the error, it is ultimately obtained experimentally, and the obtained relational form is memorized and used for defocusing with respect to temperature t. Find the error ΔP.

However, in the usage range of 20 to 30'O below L of the reference temperature tO, the relationship between the temperature t and the defocus error ΔP can be approximated linearly, so in that case, ΔP = k(t-to). . Here, k is a proportionality constant determined by the focus detection device or the imaging optical device, and it is assumed that the focus detection device is adjusted so that the defocus error ΔP becomes zero when the reference temperature is to.

Furthermore, the correction means 5 stores the defocus error ΔP, and corrects it by adding the defocus error ΔP to the output (defocus amount P) of the defocus calculation means 3.

The control means 52 is connected to the photoelectric conversion device 2 via the sensor drive means 24, sets the charge accumulation time Td for dark current measurement in a counter, instructs the sensor drive means 24 to start accumulation, and performs the above-described operation. When the counter reaches zero, the sensor driving means 24 is instructed to start the transfer. The sensor drive means 24 controls the drive of the photoelectric conversion device 2 based on this instruction.

The microprocessor 50 includes a reset means 8;
A drive display means 90 is connected to drive the photographing lens 12 or to display its drive direction based on the defocus @pr corrected by the correction means 5.

Next, the operation of the focus detection device having the configuration described in 1- will be explained using the flowchart of FIG.

First, in step (2), the microprocessor 50 is reset by the reset means 8.

Next, in step (2), the control means 52 sets the charge accumulation time Td for dark current measurement in the counter, instructs the sensor drive means 24 to start accumulation, and when the counter becomes zero, transfers the charge to the sensor drive means 24. Instruct to start. The sensor drive means 24 controls the drive of the photoelectric conversion device 2 based on this instruction.

In step ■, the data from the photoelectric conversion device 2 is
is transferred to the data memory means 51 via the converter 23,
be remembered.

In step (2), the correction means 5 takes out the dark current corresponding value Xd corresponding to the heavy pressure Vd corresponding to the dark current from the memory section of the data memory means 51 containing data corresponding to the optical black parts 21a and 22a. .

In step (2), the correction means 5 calculates the temperature t from the dark current corresponding value Xd based on the equation (1).

In step (2), the correction means 5 calculates the defocus error ΔP from the temperature t based on the method described above or the equation (2).

In step ■, the defocus error Δ obtained in this way is
P is stored in the correction means 5, and thereafter this value is added to the calculation result of the defocus amount P each time for correction.

Steps ■, ■, and [phase] are normal focus detection operations. The accumulation time during normal operation is determined using a known method.

That is, the photoelectric conversion device may monitor the average charge accumulated in the image sensor, and when it reaches a predetermined amount, it may automatically end charge accumulation and transfer the charge, or the previous result may be used to calculate the next integration. The time may be controlled by software.

In any case, when the defocus amount P is determined in step [phase] by the defocus amount calculation means 3 in this way, the correction means 5 calculates the defocus amount FT corrected in step (step) by FT=P+ΔP. calculate. Then, this defocus ri+rP T I is outputted to the outside using STEP@. The drive display means 80 displays 9 based on the value of FT.
Performs dynamic display.

After that, go back to step ■ and repeat the same cycle.

The charge accumulation time Td for dark current monitoring depends on the device, but is, for example, a value of about 0.1 to 1 sec.

In the above embodiment, only one value was used as the charge accumulation time Td, but initially the charge accumulation time Td〇-0, 1se
It is also possible to monitor the dark current as c, and when the dark current output is insufficient, to monitor the dark current again with the charge accumulation time Td' = 1 sec, for example, by changing the accumulation time a plurality of times.

In this case, (1
) formula has been created, in order to apply it to cases of other accumulation times, it is sufficient to use the value converted to the case of Tdo,
When the accumulation time is the charge accumulation time Td', the value of the dark current corresponding value Xd at that time multiplied by Td0/Tdl may be substituted into equation (1) as a new dark current corresponding value Xd.

Also, when it is dark, the storage time T is longer, so
The temperature can also be determined using the dark current corresponding value Xd regarding the output 2B of the optical black portions 2+a and 22a in the normal loop of steps ① to ②.

In this case as well, if equation (1) is created based on the accumulation time of the charge accumulation time TdO, then the value obtained by multiplying the value of the dark current corresponding value Xd at the accumulation time T by Td0/T is ( It may be calculated as the dark current corresponding value Xd in equation 1).

In the above embodiment, a case has been described in which correction is made to the oil quality result of the defocus amount, but of course correction based on temperature is added to the image shift area before the defocus amount is calculated. The defocus amount may be calculated from.

(Effects of the Invention) According to the focus detection device according to the present invention, a temperature detection means for detecting an output corresponding to temperature, and a correction means for correcting a defocus amount based on the output of the temperature detection means are provided. Therefore, accurate focus detection is possible without being affected by temperature changes.

[Brief explanation of the drawing]

Fig. 1 is an overall configuration diagram for clearly showing the configuration of the present invention, Figs. 2 to 4 show an embodiment of the invention, Fig. 2 is an overall layout diagram, and Fig. 3 is an overall configuration diagram. An output diagram of a CCD image sensor, FIG. 4 is a flowchart for explaining the operation, FIGS. 5 and 6 show conventional examples, FIG. 5 is an overall layout diagram, and FIG. 6 is a focus diagram. FIG. 7 is a perspective view showing another example of the focus detection optical device. 1... Imaging optical device 2... Photoelectric conversion equipment 3.
...Defocus amount calculating means 4...Temperature detection means 5...Correction means 8a...
・Predetermined detection surface Fig. 1 Fig. 2 Fig. 3 Fig. 1r Fig. 4 ■ Sohi ban ■ Accumulation time ATdl: zub ■ Collaborative burial mound final J and E U ξ turn (■ Ro PC secret - jbo ξ1 to , and 9 hinita'1ror to the amount of dark seeds; Chang'an - Figure 5 Figure 6 Figure 7

Claims (2)

[Claims] (1) Guide the object image of the imaging optical device onto the photoelectric conversion device,
A focus detection device that detects the focus of the imaging optical device calculates the difference between the imaging plane of the imaging optical device and a predetermined detection surface, that is, the amount of defocus, from the output of the photoelectric conversion device. A defocus amount calculation means for detecting from the temperature, a temperature detection means for emitting an output corresponding to the temperature, and a correction means for correcting the calculation content or output of the defocus amount calculation means based on the output of the temperature detection means. A focus detection device featuring: (2) The focus detection device according to claim 1, wherein the photoelectric conversion device has a CCD type image sensor, and the temperature detection means monitors a dark current of the image sensor. .