JPS62192714A - Focus detecting device - Google Patents

Abstract

PURPOSE:To make proper focus detection possible at the time of passive AF and active AF respectively by providing the first and second focus detecting sensors of different spectral sensitivity, a photometric sensor, the first and second chromatic aberration correcting means etc. CONSTITUTION:The device consists of the first focus detecting sensor 207 for active AF, the second focus detecting sensor 206 for passive AF, the first and second photometric sensors, a light projector, a mode selecting means that selects either active AF or passive AF, a light emitting circuit, an information source of chromatic aberration and the first and second chromatic aberration information correcting means. In the active AF mode, the amount of defocus signals obtained basing on output from the first focus detecting sensor 207 are correcting basing on output of the second chromatic aberration correcting means. Thereby, deviation of focus can be prevented effectively, and accordingly, good focused state focused to visible light can be obtained not only at the time of passive AF but also at the time of active AF.

Description

[Detailed Description of the Invention] 1. Presentation and Minutes ■ The present invention is a passive AF that performs focus detection relying on external light.
and Active A, which projects light of a predetermined wavelength near the boundary between visible light and infrared light onto the subject and detects focus from the reflected light.
The present invention relates to a focus detection device capable of F.

The mainstream of interchangeable lens cameras is the passive method, which does not limit the shooting distance in order to accommodate various interchangeable lenses with different focal lengths and aperture f-numbers, but when the brightness of the outside world is dark, Focus detection accuracy deteriorates or focus detection becomes impossible. Therefore, a method has been devised in which light is projected from the camera side, and the reflected light that hits the subject is received by a focus detection sensor via a photographic lens to perform focus detection. Normally, near-infrared light is used as the projection light so that it is invisible to the human eye, so in this case, one of the important points is
The brim is a measure against out-of-focus caused by chromatic aberration of the photographic lens. As an example of this measure, JP-A-59-1
There is one described in Japanese Patent No. 29839.

The technique described in JP-A-59-129839 includes a first focus detection sensor that is sensitive only to visible light and a second focus detection sensor that is sensitive only to near-infrared light,
Each photographic lens stores the amount of correction for focus error (chromatic aberration) corresponding to the difference between visible light and near-infrared light, and selects which sensor to use depending on the amount of light between visible light and near-infrared light. When focus detection is performed using the second focus detection sensor, a signal indicating the focus detection result is transmitted as a signal corresponding to the difference (chromatic aberration) between visible light and near-infrared light. The corrected signal is output, and the focus of the photographic lens is adjusted based on this signal.

In the technology described in Japanese Patent Application Laid-open No. 129839/1983, as mentioned above, the first focus detection sensor receives only visible light and the sensor receives only near-infrared light. The second focus detection sensor is configured to determine the magnitude of the light amount of visible light and near-infrared light to determine which sensor should be used for focus detection. When external light is projected, focus is detected based on the output of the second focus detection sensor, and the detection result is corrected using both the chromatic aberration of the photographing lens at the wavelength of the projected light, but the There was a drawback that the focus position shifted due to differences in the color temperature of the illuminating light source. In this case, if the wavelength range of the second focus detection sensor is narrowed to match the wavelength range of the projected near-infrared light, the above drawback can be overcome, but on the other hand, the sensitivity of the sensor becomes low. be.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a useful focus detection device that is capable of active AF as well as passive AF and that solves the above-described problems.

4. To make a prediction - The above purpose is to use passive AF, which detects focus based on external light, and to project light of a predetermined wavelength near the boundary between visible light and infrared light onto the subject and reflect it. A focus detection device for a camera capable of active AF that detects focus from light includes a first focus detection sensor that is primarily sensitive to a predetermined wavelength range that includes the wavelength of the projected light, and a second focus detection sensor that is primarily sensitive to the visible range. a first focus detection sensor having substantially the same spectral sensitivity as the first focus detection sensor;
a second focus detection sensor having substantially the same spectral sensitivity as the second focus detection sensor;
a photometric sensor; a light projector that emits the projection light; a mode selection device that selects either active AF or passive AF; a light emitting circuit that causes the light projector to emit light when active AF is selected; a chromatic aberration information source that outputs information on chromatic aberration of a photographing lens with respect to projected light; a first chromatic aberration information correcting means for correcting the chromatic aberration information output from the chromatic aberration information source based on the output of the second photometric sensor to create chromatic aberration information of the photographing lens with respect to ambient light illumination; The chromatic aberration information from the chromatic aberration information correction means and the chromatic aberration information from the chromatic aberration information source are converted into ratios of the respective output sizes of the second photometric sensor when the light emitting means is not emitting light and when emitting light. and a second chromatic aberration information correcting means for synthesizing the true chromatic aberration information of the photographing lens at the time of light projection by the light projecting means, and in the active AF mode, the output from the first focus detection sensor. A focus detection device, wherein a defocus amount signal obtained based on the defocus amount signal is corrected based on the output of the second chromatic aberration correction means.

Figure 1 shows a single-lens reflex camera equipped with a focus detection device as an embodiment of the present invention, in which 100 is a camera body, 10
Reference numeral 1 denotes an exchangeable photographic lens, and 102 denotes a reflex mirror, which reflects light that has been refracted and transmitted through the photographic lens 101 toward the finder optical system, and also transmits a portion of the light. 103 is a total reflection mirror for guiding the transmitted light of the reflex mirror 102 to the focus detection optical system 104; 105 is an optical member disposed near the planned focal plane of the photographing lens 101; is light emitting diode 1
A wavelength-selective semi-transparent part 105a that reflects light with a wavelength of 0.07 and transmits visible light is located at an angle of about 45 mm with respect to the optical axis.
It is set at an inclination of °. A prism 106 having a shape as shown in the figure is arranged on the side surface of the optical member 105, and deflects the light beam emitted from the light emitting diode 107 and introduces it into the optical member 105. A reflecting mirror 108 is disposed in the optical path of the light beam emitted from the light emitting diode 107, and serves to deflect the light beam emitted from the light emitting diode 107 downward. A first projecting lens 109 is disposed between the reflecting mirror 108 and an eyepiece 113, which is one of the components of the finder, and makes the light rays emitted from the light emitting diode 107 parallel. This first projection lens 109 and the eyepiece lens 11
3, a first light projection mask 110 is provided. This mask is used to narrow down the projected light flux. The eyepiece lens 113 also serves as a passage for light rays emitted from the light emitting diode 107. 111 is the eyepiece lens 1
13, which is a second projection lens disposed below the first
The parallel light beams are focused by the light projecting lens 109 to form an image in the vicinity of the intended imaging plane of the photographing lens 101. 1
2 is a 20th light projection mask provided immediately in front of the second light projection lens 111. With such a configuration, the light beam emitted from the light emitting diode 107 is transmitted through the light projection lens 10.
9, 111, the light is condensed by the light projection masks 110 and 112, passes through the optical axis of the photographic lens on the planned focal plane of the photographic lens, and is projected at a slight angle with respect to the optical axis of the photographic lens. This angle should be set to a sufficiently small value, such as F-4 or F-5 in terms of F-number, so that the projected light will not be vignetted by the lens barrel or aperture even when using a dark photographic lens with a large F-number. It is set to about .6.

Here, when the light emitted from the light projection optical system having the above configuration is projected onto the subject and the reflected light is received by the focus detection optical system through the photographic lens 101, as described above, due to the inter-plane reflection of the photographic lens. Harmful light is generated, and its influence will be discussed in detail based on FIGS. 8 to 13.

Fig. 8 is a diagram showing the optical arrangement relationship between the photographing lens and the focus detection optical system, and Fig. 9 is a diagram explaining the principle of focus detection, where Lo is the photographic lens, F is the focal plane, and behind it A focus detection optical system AO is arranged. Q and P are masks placed in front of the lens respectively; 1. C is CCD
This is a one-dimensional light-receiving element. The focus detection principle is already well known, so it will be omitted here (Japanese Unexamined Patent Publication No. 59
-107311 etc.).

FIG. 10 is an example of a projection optical path diagram for explaining harmful light generated by inter-plane reflection of a photographic lens. In the figure, for convenience of explanation, the projection optical system is omitted and only the light beams are shown.

A ray of light projected from a point 0 on the planned focal plane on the optical axis of the photographic lens at the angle shown in the figure is reflected by the surfaces of each lens that makes up the photographic lens, and returns to the direction of incidence with a spread as shown in the figure. come. It would be complicated to draw light rays reflected from all surfaces, so Figure 10(a) shows a typical example of 1°2.
．． It shows the rays of light that are reflected from six surfaces and return. (Single reflection) FIG. 10 (bl) shows an example in which the light returns to the incident direction after being reflected many times (three times), with the number of reflecting surfaces being 6 - 1 - 6 as an example.

Figure 11(a) shows the spread of harmful light on the 0th surface of the first mask in Figure 8, and shows how the harmful light spreads in a point-symmetric range with respect to the optical axis. has been done. Here, each circle corresponds to the spread of harmful light reflected on the surface of each lens making up the photographic lens. Although we have only shown the spread of harmful light generated by one reflection, the same applies to cases of three or more reflections.
It spreads over a point-symmetric range with respect to the optical axis. FIG. 11(b) shows the spread of harmful light on two surfaces of the second mask (diaphragm mask). The harmful light that reaches the second mask is that which has passed through the first mask. FIG. 12 shows calculations of how harmful light changes with different types of photographic lenses. Similar to FIG. 11(b),
The state on the second surface of the second mask is shown. The upper row shows the case where the photographic lens is extended to the ■ position, and the lower row shows the case where it is at the closest position.

As can be seen from this figure, a standard lens (lens configuration: modified Gauss type) with a focal ratio MItf = 50 mm and an aperture F value of F-1.
The shape of harmful light differs greatly between the 4.5 zoom lens and the 4.5 zoom lens. Also, the same f-'35-105mm, F=3.5
Even with a ~4.5 zoom lens, the appearance of harmful light changes as the zooming position changes. This is because the optical system of the photographic lens changes due to zooming. Moreover, it is for the same reason that it changes depending on the difference in the amount of delivery. As shown in Fig. 13, each of the above data is based on the following conditions: the angle θ between the light projection optical axis and the photographing lens optical axis is 5.5°, the aperture system in front of the light projection lens is 4 mmφ, and the focal length of the light projection lens. is 12 mm, and the light source is a spherical glass bulb (0
, 5mmφ) with a light emitting diode (emission diameter 40μmφ)
) is used. Further, it is assumed that the optical axis of the light projection optical system is set within a plane that includes the photographing lens optical axis and is perpendicular to the direction in which the aperture masks P are arranged.

FIG. 2 shows a focus detection optical system 104 provided in the single-lens reflex camera of FIG. 1, and in this focus detection optical system, the influence of the above-mentioned harmful light is effectively eliminated. Next, while explaining the configuration of FIG. 2, the reason why the influence of harmful light is eliminated will be described. In the figure, 200 is near the planned focal plane of the photographing lens (
This is a field mask having an elongated opening 200a in a direction parallel to the plane of the paper. 201 is the above-mentioned field mask 20
This is a colorless and transparent protective cover placed immediately after 0. A condenser lens 202 is placed immediately after the cover 201, and has the power to form an image of an aperture mask aperture, which will be described later, approximately on the exit pupil plane of the photographing lens. 2
03 is a total reflection mirror. The total reflection mirror 203 deflects the light beam that has passed through the condenser lens 202 by 90 degrees and makes it enter the beam splinter 204 .

Beam splinter 204 has a semi-transparent surface 204a and a total reflection surface 204b. The semi-transparent surface 204a is configured to transmit visible light and reflect infrared light. An aperture mask 208 is placed in close contact with the beam splinter 204 . As shown in the second report, in the aperture mask 208, two aperture apertures 208a for passive AF having a roughly elliptical shape are formed at intervals on the left and right. Two aperture apertures 208b for active AF having an elliptical shape are formed at intervals on the left and right sides. The interval m between the apertures 208b is larger than the interval l between the apertures 208a.

By setting m>/ in this way, during active AF, light rays from a brighter (smaller F value) part of the photographing lens can enter the focus detection sensor than during passive AF, and this allows the active Harmful light due to inter-plane reflection of the photographic lens can be prevented from entering the focus detection sensor during AF. A secondary imaging lens 205a is arranged behind the diaphragm aperture 208a, and a secondary imaging lens 205b is arranged behind the diaphragm aperture 208b. The original focus detection sensor (second focus detection sensor) 206 is located on the imaging plane of the secondary imaging lens 205b, and a one-dimensional focus detection sensor (first focus detection sensor) 207 such as COD is mounted on the imaging surface of the secondary imaging lens 205b as shown in FIG. (b
). Therefore, the second focus detection sensor 206 is for passive AF, and the first focus detection sensor 207 is for active AF.

FIG. 3 shows the spectral sensitivities of the focus detection sensors 206 and 207,
The spectral transmittance of the semi-transparent surface 204a of the beam splinter 204 and the emission wavelength characteristics of the light emitting diode 107 are shown. As is clear from this graph, the second focus detection sensor 20
Visible light in the range of about 400 to 7QQnm is incident on 6,
Approximately 700 to 1l100 for the first focus detection sensor 207
Light in a range of n (light with a predetermined wavelength near the boundary between visible light and infrared light) is incident.

FIG. 6(a) is a graph showing the relationship between chromatic aberration and wavelength of a nine-photographing lens. The wavelength is on the horizontal axis and the d of 589 nm is on the vertical axis.
- The amount of out-of-focus ΔIR is calculated based on the line. In FIG. 6(b), ray a indicates visible rays, and ray s indicates infrared rays. The amount of deviation ΔIR between the focus position of light ray a and the focus position of light ray A is the amount of chromatic aberration, and in the region of about 600 nm or more, the longer the wavelength, the larger ΔIR becomes.

FIG. 7 shows the relative spectral distribution of light rays generally used to illuminate a subject. From Figures 6 and 7, if the spectral sensitivity of the focus detection sensor extends to the infrared range, the photographing lens will The amount of chromatic aberration ΔIR increases, and the focus detection error increases. On the other hand, when the subject is illuminated with light that has a small amount of light in the infrared region, such as with a D light source, the photographic lens is covered.

It can be seen that the difference amount ΔIR is small and the focus detection error is small. Therefore, in the case of passive AF that cuts out light of 700nm or more, the effect of focus detection error due to the difference in light sources mentioned above can be almost ignored;
In the case of active AF that receives light of m-1l100n, it can be said that the influence of the focus detection error due to the difference in light sources described above is large. In particular, during active AF, (light from the photon light emitting diode in the outside world) is incident on the focus detection sensor, so the focal position changes depending on the amount and wavelength characteristics of the outside light.

FIG. 5 shows a block diagram of a focus detection system configured to always obtain a good in-focus state even if the focus position changes as described above. Further, FIG. 4 shows a focus detection sensor and a photometry sensor that are commonly used in the system. As mentioned above, there is a pair of focus detection sensors, but since they have the same configuration, only one is shown in FIG. Also,
For similar reasons, there are two types of photometric sensors: one that is primarily sensitive to the infrared region and one that is primarily sensitive to the visible region.
There are several types, but only one is shown. In Figure 4,
Reference numeral 300 denotes a line sensor composed of a one-dimensional photodiode as an example of a focus detection sensor, the output of which is transferred to a shift register section 304 via a transfer gate 303 and outputted from an output terminal of an operational amplifier 306 as a signal Vss. 301 is an elongated rectangular photodiode whose output is f from the output terminal of the operational amplifier 305.
It is output as No. B vAl). Photodiode 301
is a photometric sensor for measuring the amount of light incident on the line sensor 300, and is arranged near the line sensor 300. 302 is an integral clear gate for clearing the charge accumulated in the line sensor 300 when the integral clear pulse φR is at a high level. Similarly, 307 is an integral clear gate that clears the charge accumulated in the photometric sensor section when φR is at a high level. A charge transfer gate 303 transfers the charges accumulated in the line sensor 300 to the shift register section 304 when the shift pulse φT is at a high level. The charges transferred to the shift register section 304 are transferred to the clock pulse φ9. φ2. The signal Vss is transferred to the operational amplifier 306 by φ, and the signal Vss is sequentially read out.

Next, in FIG. 5, reference numeral 400 denotes a first focus detection sensor (corresponding to 207 in FIG. 2), 401 which is sensitive mainly to the near-infrared light region, which is a predetermined wavelength region between visible light and infrared light.
is a second focus detection sensor (corresponding to 206 in FIG. 2) that is primarily sensitive in the visible light range. 400S is a first photometric sensor that measures the average amount of light incident on the first focus detection sensor 400, and 401S is a second focus detection sensor 40.
a second photometric sensor that measures the average amount of light incident on 1;
02,403 is analog signal-digital signal (A/D)
The conversion circuit and CCD drive circuit A/D converts and outputs signals output from the focus detection sensors 400 and 401, and outputs driving signals to the focus detection sensors 400 and 401. 404 and 405 are storage circuits for storing the outputs of the A/D conversion and CCD drive circuits 402 and 403. A select circuit 406 selectively outputs one of the data output from the memory circuits 404 and 405 based on the output of the photometric circuit 411. 407 is an algorithm processor, and the focus detection sensor 400 or 4
01, A/D conversion and CCD drive circuit 402
Alternatively, in step 403, the signal converted into a digital signal is processed according to a predetermined algorithm to calculate the amount of defocus of the photographic lens. 408 is an arithmetic circuit that outputs a signal obtained by subtracting the output of the algorithm processor 407 and the output of the select circuit 426. 409 is a motor drive circuit,
Based on the signal output from the arithmetic circuit 408, the motor for driving the photographing lens is controlled. 410 is a trigger circuit that functions to generate a focus detection start signal in response to ON/OFF of the shirt button or a separate switch, and its output signal is sent to the photometry circuit 411 and the system controller 41.
2. The photometry circuit 411 is a trigger circuit 41
It starts its operation with a focus detection start signal output from 0, measures the brightness of the subject, and outputs a signal to the select circuit 406, select circuit 426, and system controller 412 when the brightness of the subject is darker than a predetermined level. do. When the photometric circuit 411 outputs the above signal, the select circuit 406 selects the output terminal of the memory circuit 404 from the algorithm P1. The select circuit 426 connects the input end of the I processor 407 to the input end of the divider circuit 425 to the arithmetic circuit 408.
Connect to one input end of the Furthermore, the system controller 412 is set to active AF mode.

The system controller 412 starts operating in response to a focus detection start signal output from the trigger circuit 410,
Each circuit is controlled to perform a predetermined operation in the active AF mode and the passive AF mode. Details of this operation will be described later. A gate circuit 413 is opened by the output of the photometry circuit 411 when the brightness of the subject is lower than a certain level, and transmits a signal output from the system controller 412 to the light emitting circuit 414. The light emitting circuit 414 receives this signal and causes the light emitting diode 107, which is a light projecting means, to emit light. 415 and 416
is a memory circuit; one memory circuit 415 stores a signal (average amount of light incident on the first focus detection sensor 400) obtained from the first photometric sensor 400S through the signal line i;
The other storage circuit 416 stores a signal (average amount of light incident on the second focus detection sensor 401) obtained from the second photometric sensor 401S through the signal line j. A dividing circuit 417 outputs a signal obtained by dividing the output of the memory circuit 415 by the output of the memory circuit 416. Reference numeral 418 denotes a ROM provided in the replaceable photographing lens, in which information ΔIR about the chromatic aberration of the photographing lens is stored. The value of ΔIR is the amount of chromatic aberration at the emission wavelength of the light emitting diode 107 that emits light. 419 is a multiplication circuit, which combines the output of the division circuit 417 and the ROM
The output of 418 is input and the product thereof is output.

420 is a select circuit, and system controller 412
According to the signal output through the signal line C, the ROM
The output of 418 and the output of multiplication circuit 419 are selectively output to multiplication circuit 421. The multiplication circuit 421 inputs the output of the selection circuit 420 and the output of the storage circuit 415, and outputs the product thereof. A select circuit 422 selectively outputs the signal output from the multiplication circuit 421 to the storage circuit 423 and the addition circuit 424 in accordance with the signal output from the system controller 412 through the signal line C. 42
5 is a division circuit which inputs the output of the addition circuit 424 and the output of the addition circuit 431, and outputs a signal obtained by dividing the output of the addition circuit 424 by the output of the addition circuit 431. A selection circuit 426 selectively outputs the output of the division circuit 425 and the output of zero (earth side) to the calculation circuit 408 based on the signal output from the photometry circuit 411. That is, when the brightness of the subject is darker than a certain value, the output of the division circuit 425 is input to the arithmetic circuit 408, and when the brightness of the subject is brighter than the certain value, a signal corresponding to the numerical value of zero is input to the arithmetic circuit 408.
08. 427 and 428 are gate circuits,
The signal output from the memory circuit 415 is output to the memory circuits 429 and 430 in response to the signal output from the system controller 412 through the signal line e. 431 is an adder circuit which inputs the outputs of the memory circuits 429 and 430 and outputs the added result to the divider circuit 425. 432 is a NOT circuit that inverts the signal output from the system controller 412 through the signal line e and applies it to the gate circuit 428.

Next, the operation of the above configuration will be explained.

(1) First, the operation during active AF will be explained. When the brightness of the subject is lower than a certain value, the metering circuit 4
11 outputs the output to that effect with select circuits 406 and 426,
Added to system controller 412 and gate circuit 413. The select circuit 406 is switched to input the detection signal from the first focus detection sensor 400 to the algorithm processor 407 in response to this signal. Select circuit 42
6 switches to a state in which the output of the division circuit 425 is input to the arithmetic circuit 408. The gate circuit 413 changes its gate to an open state. Additionally, the system controller 412 is set to active AF mode. System controller 4
12 is set to this mode, there are two modes: a light projection mode in which light is projected onto the subject and the reflected light is received by the first focus detection sensor 400, and a light projection mode in which light is not projected onto the subject and the reflected light from the subject is received. A non-emission mode in which light is received by the two focus detection sensors 400 and 401 is alternately performed, and the final focus position is determined based on the signals output in both modes.

The light projection mode and non-light projection mode in the active AF mode will be sequentially explained below.

■Light projection mode The select circuit 420 selects the ROM4 by the signals output from the signals IJitC and d of the system controller 412.
The output terminal of 1 B is connected to the input terminal of the multiplication port FIFr 421, and the select circuit 422 connects the output terminal of the multiplication circuit 421 to the input terminal of the storage circuit 4230.

Furthermore, a signal output from the signal line e of the system controller 412 causes the gate circuit 427 to be closed and the gate circuit 428 to be opened. Furthermore, a signal output from the signal line of the system controller 412 causes the light emitting diode to emit light for a certain period of time via the gate circuit 413.

In this light projection mode, the signal input from the first photometric sensor 400S to the memory circuit 415 through the signal line i is
When it is set to L, the output of the multiplier circuit 421 becomes BL·ΔIR, and the output of the select circuit 422 also becomes BL·ΔIR. Therefore, BL and ΔIR are stored in the storage port 178423.

However, ΔIR is the chromatic aberration information of the photographing lens stored in the ROM circuit 418. In addition, BL is stored in the storage circuit 430, and after the output of the first focus detection sensor 400 is converted into a digital signal by the A/D conversion COD drive circuit 402, the output from the selection circuit 406 is sent to the storage 11 circuit 404.
The signal stored in is output. Therefore, the algorithm processor 407 outputs the defocus amount Df as a result of processing the output signal of the select circuit 406 according to the algorithm processor.

■Non-emission mode The select circuit 420 selects the multiplier circuit 419 according to the signals output from the signal lines c and d of the system controller 412.
The select circuit 422 inputs the output of the multiplier circuit 421 to the adder circuit 421.
24. Furthermore, a signal output from the signal line e of the system controller 412 sets the gate circuit 427 to the open state and the gate circuit 428 to the closed state.

In this mode, the first photometric sensor 400
Assuming that the signal output from S through the signal line i is Bo, and the signal output from the second photometric sensor 401S through the signal line j is A, the output of the division circuit 417 is as follows:
/A multiplication circuit 419 output is ΔIR-Bo/A3Δ
The output of the IRx select circuit 420 is ΔIRx The output of the multiplier circuit 421 is Bo・ΔIRx select circuit 4
The output of 22 becomes Bo·ΔIRx. In addition, the addition circuit 4
One input of 24 (output of memory circuit 423) is BL・Δ
IR and the other input is Bo・ΔIRx, so
The output of the adder circuit 424 is: BL・ΔIR+Bo・ΔIRx Since the output of the adder circuit 431 is BO+BL, the output of the divider circuit 425 is (BL−ΔIR+Bo・ΔIRx)/(Bo+BL). As a result, the output of the arithmetic circuit 408 is Df-(B
L・ΔIR+Bo・ΔIRx)/(Bo+BL). Here, Df is the defocus amount obtained from the algorithm processor 407, and inevitably includes zero aberration. Also, (BL・ΔIR+Bo−ΔIRx)/(B
o+BL) Bo+BL Bo+BL is a correction term for chromatic aberration caused by color temperature difference. Note that ΔIRx is the amount of chromatic aberration that takes into account the color temperature of the light in the outside world, and is determined by the wavelength characteristics of the light in the outside world, the spectral sensitivity of the focus detection sensor 400, 401, and the emission wavelength of the light emitting diode. The above formula 9 formula % is merely an example, and ΔIRX does not necessarily need to be determined according to the above formula.

Also, BL/ (Bo+BL), Bo/ (Bo+BL)
are respectively shown as the ratio of the magnitude of the output of the first photometric sensor 400S when the light is emitted and when the light is not emitted, and Δ is calculated according to these ratios.
After correcting IR and ΔIRx, both are added, and as a result, true chromatic aberration information of the photographing lens is obtained, which also takes into account ambient light at the time of light projection. Here, the relationship between the sizes of BO and BL is (BL/ (Bo+BL)HBo/ (Bo+BL
) It is also possible to directly express the ratio of Bo and BL as B o /BL, and in that case, it is obvious that the configuration of the circuit block in FIG. 5 will be different.

Therefore, the signal obtained from the output of the arithmetic circuit 40B is the amount of defocus with chromatic aberration corrected. (When the above-mentioned signal is obtained from the arithmetic circuit 408, a signal is output from the system controller 412 through the signal line r, and the motor drive circuit 409 is driven to adjust the focus of the photographing lens.

(2) Next, the operation during passive AF will be explained.

In this case, the output of the photometric circuit 411 causes the select circuit 406 to switch to input the focus detection from the second focus detection sensor 401 to the algorithm processor 407, and the select circuit 426 sends a zero signal to the calculation circuit 408. Switch to output. Further, the gate circuit 413 is closed, and the system controller 412 is set to passive AF mode via the signal line g. When the system controller 412 is set to the passive AP mode, the light emitting diode does not emit light, and therefore, focus adjustment is performed every time a signal is output from the second focus detection sensor 401. In this case, since the second focus detection sensor 401 has sensitivity mainly in the visible range, out-of-focus due to chromatic aberration is unlikely to occur, and therefore chromatic aberration correction is not performed.

As explained above, the present invention is equipped with two focus detection sensors with different spectral sensitivities, so it is possible to use focus detection sensors with appropriate spectral sensitivities for passive AF and active AF, respectively. You can choose.

In addition, during focus detection in active AF mode, even if external light enters the focus detection sensor, chromatic aberration correction based on it is performed first. Since this is performed by the second chromatic aberration correction means, defocus can be effectively prevented, and therefore, a good focusing state in which visible light is in focus can be obtained not only during passive AF but also during active AF.

[Brief explanation of drawings]

FIG. 1 is a perspective view of a single-lens reflex camera equipped with a focus detection device as an embodiment of the present invention, and FIG. 2(a) is a side view showing the focus detection optical system used in the camera of FIG. , the same figure (bl is a plan view of figure (al), Figure 3 is a diagram showing the spectral sensitivity of the light emitting diode, CCD line sensor, etc. used in the device of the present invention, Figure 4 is the electrical diagram of the focus detection sensor and photometric sensor. FIG. 5 is a block diagram showing an example of the detection system of the focus detection device of the present invention, and FIG. 6 (al.
FIG. 6 is a diagram showing the relationship between chromatic aberration of a photographic lens and wavelength, and FIG.
Fig. 7 is a diagram showing the relative spectral distribution of various light sources, and Figs. 8 to 13 are diagrams explaining harmful light due to inter-plane reflection of the photographic lens. A diagram showing the optical arrangement with the system, Figure 9 is a diagram of the principle of focus detection, Figures 10 (a) and (b) are diagrams showing the state of reflection between surfaces, and Figure 11 (a) (bl is the surface Figure 12 is a diagram explaining the influence of harmful light due to interreflection, Figure 12 is a diagram explaining the influence of harmful light on various lenses, and Figure 13 is the projection optical axis of the optical system used to measure the harmful light in each of the above figures. 101... Photographing lens, 107... Light projecting means, 20
6 (401)...Second focus detection sensor, 207(
400)...first focus detection sensor, 400S...
1st photometric sensor, 401S... 2nd photometric sensor, 428... Chromatic aberration information source, 406.426, 412, 413... Mode selection means, 414... Light emitting circuit, 415.416, 417 .419...first chromatic aberration information correction means, 420.421, 422, 423, 425, 427.4
28,429,430.431...Second chromatic aberration information correction means. Patent applicant: Minolta Camera Co., Ltd. Figure 1 Figure 2 (a) Figure 2 (b)

Claims (3)

[Claims] (1) Passive AF, which detects focus by relying on external light, and active AF, which projects light of a predetermined wavelength near the boundary between visible light and infrared light onto the subject and detects focus from the reflected light.
A focus detection device for a camera capable of A first focus detection sensor having approximately the same spectral sensitivity as the first focus detection sensor.
a second focus detection sensor having substantially the same spectral sensitivity as the second focus detection sensor;
a photometric sensor; a light projector that emits the projection light; a mode selection device that selects either active AF or passive AF; a light emitting circuit that causes the light projector to emit light when active AF is selected; a chromatic aberration information source that outputs information on chromatic aberration of a photographing lens with respect to projected light; and chromatic aberration output from the chromatic aberration information source based on the outputs of the first and second photometric sensors when the light projecting means is not projecting light. a first chromatic aberration information correcting means for correcting information to create chromatic aberration information of the photographing lens with respect to ambient light illumination; and chromatic aberration information from the first chromatic aberration information correcting means and chromatic aberration information from the chromatic aberration information source; The true chromatic aberration of the photographing lens when the light emitting means emits light is calculated by combining the outputs of the second photometric sensor when the light emitting means is not emitting light and when the light emitting means is emitting light. and a second chromatic aberration information correction means for producing information, and in active AF mode, a defocus amount signal obtained based on the output from the first focus detection sensor is sent to the output of the second chromatic aberration correction means. A focus detection device that performs correction based on the following. (2) The mode selection means includes a photometric circuit that measures the brightness of the subject, and is configured to select the active AF mode when the brightness of the subject is below a predetermined level. A focus detection device according to claim (1). (3) Claims (1) or (2) characterized in that the projection light is configured so that it passes through the photographic lens from the rear to the front and is projected toward the subject. The focus detection device described.