JPS62180314A - Focus detecting device - Google Patents

Abstract

PURPOSE:To avoid the influence of a harmful light, and to detect a focus by an active system, by providing the first and the second projecting means, a secondary image forming means, at least two pairs of diaphragm apertures, a switching means, a photodetecting sensor, and a selecting means, and execut ing a detection of a focal position of a photographic lens from an output signal of the photodetecting sensor. CONSTITUTION:When brightness of an object is below a prescribed level, a selecting circuit 312 dedides which of the light emitting diodes 308 and 309 is to be made to emit a light beam, based on information from a lens ROM 307, and the light emitting diode 308 or 309 of the selected side emits a light beam. A reflected light passes through photodetecting sensors 300, 301 of the selected side by a selecting circuit 304, A/D converting and CCD driving circuits 302, 303 and the selecting circuit 304, and inputted to an algorithm processor 305. The algorithm processor 305 processes an inputted data in accordance with an algorithm, and calculates a defocus quantity of a photographic lens. Based on the calculated defocus quantity, a motor driving circuit 306sis driven, and focusing of the photographic lens is executed.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an active type focus detection device suitable for an eye reflex camera.

There are two focus detection methods for laser cameras: a passive method that uses external light to detect the focal point, and an active method that detects the focal point by projecting light and detecting the reflected light from the subject. There is a method. - In reflex cameras, passive methods with no limitations on shooting distance are mainstream in order to accommodate various interchangeable lenses with different focal lengths and aperture f-numbers, but focus detection accuracy is poor when the outside brightness is dark. The drawback is that the focus may become distorted or the focus cannot be adjusted. Therefore, the present applicant previously proposed a system in Japanese Patent Application No. 1986-76.86 in which an auxiliary illumination device is incorporated into a flash and focus detection can be performed even in the dark. An outline of this proposed technology is shown in FIG.

In the figure, 1 is a camera body, 2 is an exchangeable photographic lens, and a focus detection module 3 receives a subject image formed by the photographic lens 2 to perform focus detection. The range defined by Su and SR that is symmetrical with respect to the optical axis OA of the photographing lens is the focus detection area. A flash 4 that is detachable from the camera is provided with an auxiliary illumination device 5,
Projecting light from this auxiliary lighting device 5 during dark times such as at night,
It is configured to perform focus detection by detecting reflected light. The auxiliary illumination device 5 is arranged at a distance Bo from the optical axis OA of the photographic lens and inclined at an angle θ, and projects light having a spread defined by Ru and Rj2. OB is the optical axis of the projection light.

In the above focus detection system, the projected light illuminates the focus detection area from an angle corresponding to the distance (Bo) between the illumination optical system and the focus extraction optical system. Illuminable distance area (
There is a natural limit to the range shown in the figure. In order to lengthen this distance range that can be illuminated, it is necessary to widen the irradiation angle of the projection light, but this reduces the illuminance at the subject, so the distance at which focus can be detected does not increase in the end.

There is also the problem of not being able to detect focus when you are not carrying a flash.

The above problem can be solved by the method disclosed in Japanese Patent Application Laid-Open No. 54-155832, in which light is projected through a photographic lens, and the light reflected by the subject is received by a focus detection sensor through the same photographic lens. However, in this case, it is necessary to take measures against the harmful light that the projected light reflects between the surfaces of the lenses constituting the photographic lens and enters the focus detection sensor.

There is a technique described in Japanese Patent Laid-Open No. 57-22210 that is devised to prevent such harmful light from entering the focus detection sensor. This prior art is based on the optical axis for projection and light reception (focus detection) on the main plane of the χ lens.
The main idea is to arrange the optical axis so that it does not satisfy a point-symmetric relationship with the optical axis.

According to optical theory, if the light-emitting optical axis and the light-receiving optical axis are arranged on the principal plane so that they are not point symmetrical with respect to the optical axis of the photographing lens, then reflection between the surfaces of the Tokuhiko lens will occur. The effects of harmful light can be removed.

By the way, in order to apply the above-described focus detection system to a single-lens reflex camera, it must be compatible with all of the various interchangeable lenses with different aperture F numbers and focal lengths. To do this, it is necessary to place the light emitting and receiving optical axes near the optical axis of the photographic lens in order to accommodate the expected smallest pupil diameter of the photographic lens. If the optical axis and the light-receiving optical axis are set close to the optical axis of the photographing lens, the influence of harmful light cannot be eliminated as theoretically possible.

Here, we will explain in some detail the harmful light caused by inter-plane reflection of the γ-photographing lens when light is irradiated onto the subject through the I-most shadow lens and the reflected light is received to perform focus detection. Fig. 9 is a diagram showing an example of a focus detection optical system that generates harmful light, and Fig. 10 is a diagram viewed from a direction 90 degrees different from Fig. 9. In the figure, LO is a photographing lens, and F is a diagram. This is a focal plane, behind which a focus detection optical system AO is arranged. Q and P are masks placed in front of the lenses, and C is a light receiving element such as a COD.

FIG. 11 is an example of an optical path diagram of a light projection optical system for explaining harmful light generated by inter-plane reflection of a photographic lens.

For convenience of explanation, the projection optical system is omitted and only the light beam is shown.

A ray of light projected from a point O on the planned focal plane on the optical axis of the photographing lens at an angle as shown in the figure is reflected by the surfaces of each lens that makes up the photographic lens and returns in the direction of incidence. (A) shows light rays that are reflected from one surface, two surfaces, and six surfaces and return as a typical example. (One reflection) Figure 11 (
B) shows an example of three reflections. (Reflecting surfaces 6 - 1 and 6) FIG. 12 (A) shows the spread of harmful light on the 0th surface of the first mask in FIG. 9,
It is shown that the harmful light spreads over a point-symmetric range with respect to the optical axis. Note that each circle corresponds to the spread of harmful light reflected on the surface of each lens making up the photographic lens. Although only the spread of harmful light caused by one reflection is shown here, the same applies to three or more reflections. FIG. 12(B) shows the second mask (aperture mask) 2
This shows the spread of harmful light on a surface. Second
Since the harmful light reaching the first mask has passed through the first mask, the harmful light is considerably reduced.

FIG. 13 shows calculations of how harmful light changes with different types of photographic lenses. Similar to FIG. 12(b), this is on the second surface of the second mask. The upper row shows when the photographing lens is extended to the ■ position, and the lower row shows when it is at its closest position.

As you can see from the figure, a standard lens with a focal length of f = 50 mm and an open F value of F = 1.7, and f = 35-1051.
-, the shape of harmful light is significantly different from a zoom lens of F=3.5-4.5. Also, the same 35-105
Even with a /3.5-4.5 zoom lens, the spread of harmful light changes depending on the zooming position. This is because the optical system of the photographic lens changes due to zooming.

For example, for (L)'s 1051 meetings, (S)'s 351 ■
In this case, the influence of harmful light is significant. Furthermore, even if the amount of payout changes, it will change slightly.

In this way, the aperture mask P is close to the optical axis of the photographing lens (
In the case of FIG. 13, the range from F'-6 to F'-16 is observed. ), the shadow of harmful light V3 caused by zooming or moving out is large, and therefore
It is understood that the influence of harmful light cannot be eliminated by the technique disclosed in Publication No. -22210. The explanation regarding the above harmful light is based on the assumption that the angle between the light emitting optical axis and the photographing lens optical axis is 5.5 degrees, and the aperture diameter in front of the light emitting lens is 41 degrees, as shown in Fig. 14.
The focal length of the light projecting lens was 12 mm, and a light emitting diode (emission diameter: 40 μm) with a spherical glass ball (diameter: 0.5 μm) was used as the light source. Also,
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 orthogonal to the direction in which the aperture masks P are arranged.

Based on the above considerations, the present invention provides a focus detection device that is skillfully devised to be less susceptible to the effects of harmful light. In the active focus detection method, there is a first light projection optical system (TTL illumination) that projects light onto the subject through the photographic lens, and a second light projection optical system (external light projection system) that emits light from outside without passing through the photographic lens. On the other hand, there is a first focus detection system that receives reflected light from the subject through an optical path close to the optical axis of the photographic lens, and a first focus detection system that receives light reflected from the photographic lens through the optical axis. It has a second focal point output system that receives light through a separate optical path, and the TTL illumination and the external light illumination, and the first focus detection system and the second focus detection system, depending on the type of photographic lens. This system consists in that the system can be selectively switched and used.

The number of the second focus detection systems is not limited to one, and systems having different distances from the optical axis of the photographic lens may be provided.

According to the above configuration, there are four or more types of combinations of the illumination system and the focus detection system. Therefore, in the case of a photographing lens with a small pupil diameter (large F value), if there is a harmful light shadow B in the combination of TTL illumination and the first focus detection system, then the combination of external light illumination and the first focus detection system Shape of harmful light 3 by selecting the combination
In addition, if there is HW of harmful light depending on the amount of extension even with a photographic lens with a large pupil diameter, TTL illumination - second focus detection system or external light illumination - can be used.
By selecting a combination of the first or second focus detection system, it is possible to effectively prevent the echo of harmful light.

The selection of one of the combinations of illumination system and focus detection system differs depending on the individual photographic lens, so the contents necessary for selecting the combination are stored in the storage means, such as a ROM circuit, for each photographic lens. It is advisable to remember it.

In that case, the selection criteria is that the illumination system should give priority to TTL illumination, which has a wide range of illumination distances, and the focus detection system should give priority to a second focus detection system that is less susceptible to the shadows of harmful light. .

FIG. 1 shows an embodiment of a single-lens reflex camera having a focus detection device according to the present invention. In the figure, 100 is a camera body, 101 is an exchangeable photographing lens, and 102 is a reflex mirror, which refracts the light that has passed through the photographic lens 101 and reflects it in the direction of the viewfinder optical system. Transmits light. 103 is a total reflection mirror for guiding the transmitted light to a focus detection optical system 104. 105
is an optical member disposed near the planned focal plane of the photographic lens 101, and in the center thereof is a wavelength-selective half mirror 105a that reflects light of the wavelength emitted from the light emitting diode 107 and transmits visible light. is approximately 45% relative to the optical axis.
It is set at an inclination of °. A prism 106 is disposed facing 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. Reference numeral 108 denotes a reflecting mirror, which serves to bend the light beam emitted from the light emitting diode 107 downward. A third projection lens 109 is disposed between the reflecting mirror 108 and the eyepiece 113, which is a component of the finder.
Make the rays emitted more parallel. A first light projection mask 110 is provided between the first light projection lens 109 and the eyepiece 113 and immediately before the first light projection lens 109 . This mask is used to narrow down the projected light flux.

Note that the eyepiece lens 113 also serves as a passage for light rays emitted from the light emitting diode. 111 is the eyepiece lens 11
3, which focuses the light rays made parallel by the first projection lens 109 and forms an image near the planned imaging plane of the photographing lens 101. 1
Reference numeral 12 denotes a second light projection mask provided immediately in front of the second light projection lens 111.

According to this configuration, the light beam emitted from the light emitting diode 107 passes through the light projection lenses 109 and 111 and the light projection mask 110.
, 112, passes through the optical axis of the photographic lens on the predetermined focal plane of the photographic lens, and is projected at a slight angle inclination to the optical axis of the photographic lens. This tilt angle should be set to a sufficiently small value so that the projected light will not be vignetted even when using a dark photographic lens with a large F value, for example, F = 4 to 5.6 in terms of F value. be.

The constituent members 105 to 113 described above constitute a first light projection optical system.

114 is another light emitting diode, pentaprism 1
It is located at the front upper part of 18. A prism 115 bends the light beam emitted from the light emitting diode 114 in front of the camera. 116 is the prism 11
This is a light projecting lens disposed opposite to the surface from which the light beam No. 5 is emitted, and collects the light beam emitted from the light emitting diode 114 and emits it toward the subject. Reference numeral 117 denotes a panel provided in front of the light projecting lens 116, and a wedge-shaped convex portion 117a is formed in a part of the panel. This wedge-shaped convex portion 117a has the function of deflecting a portion of the light rays emitted from the projection lens 116 downward (in the direction of the optical axis of the photographing lens in the figure) to illuminate a nearby object. The constituent members 114 to 117 described above constitute a second light projection optical system.

Next, FIG. 2 shows a detailed diagram of the focus detection optical system 104. In the figure, 200 is a photographing lens, and 201
is a field mask placed near the intended focal plane of the χ lens 200. 202 is a condenser lens placed immediately after the field mask 201, and a diaphragm plate 204 to be described later.
, 205 are formed near the exit pupil of the photographic lens 200. Reference numeral 203 denotes a deflection optical member disposed behind the condenser lens 202, and as shown in both the rear view of FIG. Reflective surfaces 203a to 203e are formed. reflective surface 2
03a and 203C are field apertures 2 of the field mask 201
They are arranged symmetrically across the optical axis OC along the longitudinal direction of 01a, and the light rays reflected by those surfaces are directed in the same direction (optical axis
The reflective surface 203b is formed so as to reflect the light upward at right angles to the reflective surfaces 203a and 203c.
The reflective surfaces 203d and 203e are inclined at 90 degrees to the field mask 20, and the light rays reflected on this surface travel in the opposite direction to the light rays reflected on the reflective surfaces 203a and 203c.
The reflective surfaces 203d and 2 are arranged symmetrically along the short side direction of the field aperture 201a of No. 1 with the optical axis OC in between.
03a, 203c and the reflective surface 203e are reflective surfaces 203b
has the same slope as . This deflection optical member 203 acts so that the light rays from the inside and the outside of the exit pupil of the photographing lens 200 form images at different locations on the light receiving element substrate 21O. That is, outside the exit pupil (a, a'
) from the reflective surface (203a) of the deflection optical member 203.
, 203 c), and after being reflected, the reflection surface 2
03d, is reflected, and enters the secondary imaging lens (206, 2
07) and the secondary imaging lens (206, 207)
An image is formed on the line sensor 211. Inside the exit pupil (
The light beams from b, b') are reflected by the reflective surface 2 of the deflection optical member 203.
After being reflected by 03b and 2030, the secondary imaging lens (2
08, 209), the image is formed on the line sensor 212.

204 and 205 are aperture slopes arranged immediately after the deflection optical member 203, and limit the area of the light beams incident on the secondary imaging lenses 206 to 209. A and A' are apertures provided in the diaphragm plate 204, which regulate the optical path of the light beam reflected by the reflecting surface 203d and exiting from the deflection optical member 203. B and B' are apertures provided in the aperture plate 205, and the reflecting surface 203
The optical path of the light beam reflected by e and exiting from the deflection optical member 203 is regulated.

The secondary imaging lenses 206 and 207 have the aperture aperture A.
, A', and is arranged in the optical path of the light beam passing through the light receiving element substrate 210.

The secondary imaging lenses 208 and 209 have the above-mentioned aperture apertures B and B.
The field aperture 201a is arranged in the optical path of the light beam passing through the light receiving element base Ji210, and is configured to form an image on the line sensor 212 arranged on the light receiving element base Ji210.

FIG. 3 shows a block diagram of an example of the focus detection device of the present invention, and in the figure, 300 is a first light receiving sensor, which corresponds to, for example, the line sensor 211 in FIG. 2. 3
01 is a second light receiving sensor, which corresponds to the line sensor 212 in FIG. 2, for example. 302 and 303 are A/
D conversion and CCD drive circuit, the light receiving sensor 30
The signal outputted from 0.301 is A/D converted and outputted, and a signal for driving is outputted to the light receiving sensor 300.301. The select circuit 304 is an A/D conversion CC
One of the data output from the D drive circuits 302 and 303 is selected and output to the algorithm processor 305. The algorithm processor 305 processes input data according to a predetermined algorithm and calculates the amount of defocus of the photographic lens. 306 is a motor drive circuit that controls a motor for driving the photographing lens based on information obtained by the algorithm processor 305. 3
Reference numeral 07 denotes a ROM provided for each photographic lens, in which information on the F number and harmful light is fixedly stored. Information on the F value is given to the select circuit 304 through the data line a, and the select circuit 304 performs A/D conversion, C
Information on the OD drive circuit 302 or 303 is selectively output to the algorithm processor 305. That is, when the F value of the photographic lens is larger than a predetermined constant value (dark lens), the light receiving sensor 301 (see FIG. The output of the line sensor 212) is converted to A/D by the CCD.
The drive circuit 303 converts it into a digital signal and outputs it to the algorithm processor 305. On the other hand, when the F value of the photographic lens is smaller than a predetermined constant value (bright lens), the light receiving sensor 300 (see FIG. The output of the line sensor (corresponding to the line sensor 211) is converted into a digital signal by A/D conversion and a CCD drive circuit 302, and output to the algorithm processor 305. 308 is a first light emitting diode, which is lit by a signal from the light emitting circuit 310. , lights out is controlled. The first light emitting diode 308
This corresponds to 107 in the figure. A second light emitting diode 309 is turned on and off by a signal from a light emitting circuit 311. The second light emitting diode 309 corresponds to 114 in FIG. The light emitting circuits 310 and 311 are selectively driven by the output signal of the select circuit 312. The selection circuit 312 selects the output of the photometry circuit 314 as R.
Based on the harmful light information output from the OM 307, it is selectively output to either of the light emitting circuits 310 and 311.

In other words, even if the distance between the aperture apertures (the distance between the apertures A, !:A' formed in the aperture plate 204 in FIG. 2 or the apertures B and B' formed in the aperture Fj, 205) is narrow ( ′) If there is no if of harmful light (in this case, the distance between the diaphragm apertures is wide, and even if it is A and A′, there is of course no 9 for harmful light), and if the distance between the diaphragm apertures is wide ( In the case of A and A') If there is no effect of harmful light but there is an effect if the space is narrow,
The output of the photometric circuit 314 is output to the light emitting circuit 310.

On the other hand, even if the distance between the aperture apertures is wide (in the case of A and A'), if there is an influence of harmful light (in this case, the distance between the aperture apertures is narrow, and even if it is B-B', the harmful light M59 will naturally occur). ), the output of the photometric circuit 314 is output to the light emitting circuit 311.

Depending on the type of photographic lens, which light emitting diode 30
Table 1 shows the selection of whether to emit light from the lens 8 or 309 and which diaphragm aperture should receive the light.

Table 1 (Active mode) The photometry circuit 314 measures the brightness of the subject, and when the photometry value is below a predetermined level, the selection circuit 312
A signal for lighting the light emitting diode is output to the light emitting circuit 310 or 311 via the light emitting circuit 310 or 311. When the photometric value of the photometric circuit 314 is equal to or higher than a predetermined level, the photometric circuit 31
4 does not output a signal to the select circuit 312. Therefore,
Neither light emitting diode 308, 309 emits light. In this case, focus detection is performed in passive mode using external light. In this mode, the F of the photographing lens is
The apertures selected for the values are as shown in Table 2.

Table 2 (passive mode) The trigger circuit 313 generates a focus detection start signal in response to the ON/OFF of the shutter button or a separate switch, and this signal is sent to the photometry circuit 314 and the A/D.
The signal is applied to the conversion and CCD drive circuits 302 and 303.

315 is an OR circuit, A/D conversion, CCD drive circuit 30
When a CCD drive stop signal is transmitted from 2, 303 to the light receiving sensors 300, 301, the signal is taken in via signal lines c, d and transmitted to the light emitting circuits 310, 311 to cause the light emitting diodes 308 and 309 to emit light. make it stop.

According to the above configuration, when the shirt button is pressed or a separate switch is turned on, the trigger circuit 313 issues a focus detection start signal, drives the photometry circuit 314, and measures the brightness of the subject. If the brightness is above a predetermined level, focus detection is performed in passive mode, while if it is below a predetermined level, focus detection is performed in active mode. Pensive mode uses external light to detect focus, and differs from active mode in that the light emitting diode 3
Since the only point is that 08 and 309 are not lit, the description will be omitted here, and the focus detection operation in the active mode will be explained.

If the brightness of the subject is below a predetermined level, the selection circuit 312 selects which light emitting diode 308 or 309 should emit light based on information from the lens ROM 307. Then, the light emitting diode 30 on the selected side
8 or 309 emits light.

The light reflected from the subject accompanying this light emission is sent to the select circuit 3.
Light receiving sensor 300.301 on the side selected in 04, A/
The signal is inputted to the algorithm processor 305 through the D conversion, CCD drive circuits 302 and 303, and the selection circuit 304. The algorithm processor 305 processes the input data according to an algorithm and calculates the amount of defocus of the photographing lens. The motor drive circuit 306 is driven based on the defocus amount thus calculated, and the photographing lens is focused.

Next, FIG. 4 shows another embodiment of the focus detection optical system. In this embodiment, an electro-optical system element 403 such as an ECD whose transmittance is locally variable is provided immediately before the secondary imaging lenses 401 and 402, and outside the exit pupil of the photographing lens 200 <a, a')
The light rays from the inside and the light rays from the inside (b, b') are made to selectively enter the line sensor 404 by changing the transmittance locally of the electro-optical element 403.

According to this embodiment, structurally, the polarizing optical member 203 is unnecessary compared to the focus detection optical system shown in FIG.
The number of secondary imaging lenses and light receiving sensors can be halved. Therefore, there is no need for the selection circuit 304 to select the signals from the light receiving sensors 300, 301 as shown in FIG. However, in order to change the transmittance of the electro-optical element 403 locally, it is necessary to control the electro-optical element 403 by the select circuit 304. FIG. 5(A) is a plan view of a member 405 incorporating the electro-optical element 403, and FIG. 5(B) is a sectional view taken along line XX.

In Figure 5 (A) and Figure 5 CB), 431-4
43 corresponds to the electro-optical element 403. 423 is a diaphragm plate, and two diaphragms 423a and 423b are formed on this plate.

The configuration of the electro-optical element 403 will be explained below.
Reference numeral 31 denotes a colorless and transparent glass plate, on the surface of which the aperture plate 423 described above is provided in close contact.

In addition, on the other surface of the glass plate 432, as shown by the dotted line in FIG.
．． Second divided transparent conductive films 432 and 433 are formed. The first divided transparent conductive film 432 is formed in areas A and A' of the apertures 423a and 423b formed on the aperture slope (Fig.
) to cover the shaded area).
On the other hand, the second divided transparent conductive film 433 is formed to cover the B and B' regions. 434 is an electrochromic film such as tungsten oxide or iridium hydroxide, and 441 is an electrolyte. When the electrochromic material is tungsten oxide, the material is colored by setting the electrode in contact with it to a negative potential and applying electricity, and in the case of iridium hydroxide, it is colored by setting the electrode to a positive potential and applying electricity. 443 is a glass plate, and a common conductive film 442 is coated on the inner surface thereof. 435 and 436 are sealing materials, and 437 and 438 are first sealing materials, respectively.
．． A conductor electrically connected to the second divided transparent conductive film 432, 439,
4.40 is a conductor connected to the common transparent electrode film 442 by 4iffl. When the electrochromic material is tungsten oxide, if electricity is applied between the conductors 437 and 439 so that the conductor 437 has a negative potential, the transparent conductive film 432 will be colored.
Since the areas are colored, areas A and A of the apertures 423a and 423b are colored. Furthermore, if electricity is applied between the conductors 438 and 440 so that the conductor 438 has a negative potential, the portion of the transparent conductive film 433 will be colored.
The B and B' regions of 23b are colored.

FIG. 6 shows the spectral transmittance of the electrochromic material. Curve (I) shows the characteristics when decolored,
Curve (n) shows the characteristics when colored. When coloring,
Absorption especially in the near infrared region increases compared to the visible region. If the wavelength of the LED light source for light projection is selected to be near infrared 700 nm or more, the electrochromic material will function as a shutter in this wavelength range. Now, aperture 423a,
If the A and A' areas of 423b are colored, light will pass through only the B and B' areas, so you will be looking at the area near the optical axis. On the other hand, if areas B and B' are colored, only areas A and A' will transmit light, so the user will be looking at areas farther from the optical axis. By switching the light transmission area in this manner during active AF, it is possible to eliminate the influence of flare and ghost caused by inter-plane reflection of the photographic lens.

Although the electrochromic element has been described above as an example of means for switching the aperture, it should be noted that liquid crystals, electro-optic cells, and even mechanical shutters may also be used.

FIG. 7 shows an optical filter (If) placed in the optical path of the focus detection optical system shown in FIG. 4, for example, at a position immediately before the field mask.
This figure shows the relationship between (I[I) (not shown in FIG. 4) and the emission wavelength (I) of a light emitting diode.

The optical filter (Il) is for cutting infrared light and eliminating the effects of chromatic aberration of the photographic lens, and the optical filter (III) is for cutting ultraviolet light (approximately 4501 or less) and is used for coloring. Electrochromic device (ECD)
) to make the light blocking function more efficient.

Since the focus detection device according to the present invention is constructed as described above,
Even if various types of photographic lenses are used, active focus detection can be performed in a state where it is difficult to receive harmful light type 1, and it is extremely useful for reflex cameras.

[Brief explanation of drawings]

FIG. 1 is a perspective view of a single-lens reflex camera to which the focus detection device of the present invention is applied, FIG. 2 is a diagram showing a focus detection optical system used in the device of the present invention, and FIG. 3 is a focus diagram as an example of the device of the present invention. FIG. 4 is a block diagram showing the detection system, FIG. 4 is a diagram showing another embodiment of the focus detection optical system, FIG. 5 (A) is a plan view showing the vicinity of the electro-optical element, and FIG. FIG. 6 is a diagram showing the transmittance characteristics of the electro-optical element, and FIG.
The figure shows the wavelength-transmittance characteristics of the optical filter and light emitting diode arranged in the optical path of the embodiment shown in Fig. 4, and Fig. 8 (A
) is a perspective view of a single-lens reflex camera equipped with a conventional focus detection device, and Figure (B) is a diagram showing the focus detection area of the camera.
Figures 9 to 14 are diagrams for explaining harmful light.
The figure shows the focus detection optical system, and Figure 10 is the same as Figure 9.
Figures 11 (A) and 11 (B) are diagrams showing the generation of harmful light, respectively, and Figure 12 (A) is a diagram showing the spread of harmful light on the first mask surface. Figure (B) is the second
Figure 13 is a diagram showing the spread of harmful light on the mask surface, Figure 13 is a diagram showing the spread of harmful light in various lenses, Figure 14 is Figure 11. It is a figure which shows the specific structure of the light projection optical system used for the measurement of harmful light from to the previous time. 107.308... is the first light projecting means 114.309
... is the second light projecting means 206 to 209, 401, 40
2...Secondary imaging means 204A, A', 205B, B'...Aperture aperture 312
...Switching means (select circuit) 211, 212, 30
0,301... Light receiving sensor 304... Selection means (select circuit) 403... Electro-optical element patent applicant Minolta Camera Co., Ltd. Figure 1 Figure 4

Claims (2)

[Claims] (1) A first light projection means that projects light through the photographic lens from behind the photographic lens; a second light projection means that projects light from outside the photographic lens; and a second light projection means that projects light from outside the photographic lens; at least two pairs of aperture apertures arranged at at least two positions at different distances from the optical axis of the photographing lens in the immediate vicinity of the secondary imaging means; and the first light projection. a switching means for switching between the first light projecting means and the second light emitting means; at least two light receiving sensors that receive light passing through the at least two pairs of apertures; and one of the two light receiving sensors in response to switching of the switching means. A focus detection device, comprising: selection means for selecting a focus position of a photographing lens from an output signal of the light receiving sensor. (2) A first light projection means that projects light from behind the photographic lens through the photographic lens; a second light projection means that projects light from outside the photographic lens; an electro-optical element disposed in the immediate vicinity of the secondary imaging means; a switching means for switching between the first light projecting means and the second light projecting means; At least one receiving light that has passed through the next imaging means
The electro-optical element functions as an aperture aperture by varying the transmittance of light at at least two locations having different distances from the optical axis of the photographing lens, and A focus detection device, characterized in that it is configured to switch the change in local transmittance in conjunction with the switching means, and thereby detect the focal position of the photographing lens from the output signal of the light receiving sensor.