JPS58156909A - Detector for focusing state - Google Patents

Abstract

PURPOSE:To reduce the difference in the incident angle of luminous fluxes and to enable the accurate decision of focusing by disposing optical systems for correction in front of sensors in order to decrease the incident angle of the image- forming luminous fluxes incident to the sensors. CONSTITUTION:Field lenses 10a, 10b for correction are disposed just before sensors 5a, 5b. The front focuses of the lenses 10a, 10b exist at the rear principal points Ha, Hb of image-forming lenses 4a, 4b. A stop 11 and the pupil P of the 1st image-forming system are in a conjugate relation with respect to a field lens 3, and the stop 11 is formed an image in the pupil P. A stop 12 is a field stop which determines the field of secondary image-formation. The ray (la) past the principal point Ha of the lens 4a is made incident perpendicularly to the face of the sensor 5a after passing through the lens 10a. The same holds true of the ray (la') that emits from the image-forming point FO' on the outside of the optical axis O. The same applies to the other image-forming system 4a, 10b, 5a as well. The difference in the outputs owing to a difference in the incident angle of the luminous fluxes is thus reduced and the accurate decision of focusing is made possible.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is particularly applicable to - in an eye reflex camera, a video camera, etc., using an imaging light beam that has passed through a photographic lens,
The present invention relates to a focus state detection device for detecting in-focus/out-of-focus or automatic focusing.

More specifically, an imaging light beam including a defocused image on a predetermined imaging plane or a plane conjugate thereto by a first imaging system of a camera or the like is converted into at least two series by a second imaging system. The images on each sensor are guided to the photosensor array, and the focusing and
This invention relates to an improvement of a focus state detection device that detects an out-of-focus state.

FIG. 1 shows an example of a conventional secondary imaging type focusing state detection device, in which 1 is a photographing lens, 2 is its aperture, and F is an image plane that is conjugate with the film. Photography lens 1
A field lens 3 is arranged behind the image plane F with the optical axis O being the same.

Behind that, a secondary imaging system consisting of two secondary imaging lenses 4a and 4b is arranged in parallel, and the primary images on the image plane F are COD, M
The image is re-imaged on a photosensor 5 such as an OS. The sensors 5 are provided in two lines 5a and 5b corresponding to the two imaging lenses 4a and 4b, and a primary image by the photographing lens l, which is the first imaging system, is formed on the image plane F. - If the sensor arrays 5a and 5b are aligned, exactly the same image is formed on the sensor arrays 5a and 5b. When the image by the photographing lens 1 is formed at the front focus, that is, at the front of the image plane F,
The images on the two sensors 5m and 5b move inward, ie, toward the light flux 0 side of the first imaging system, as shown by the arrows. The field lens 3 has a conjugate relationship between the secondary imaging lenses 4a and 4b and the exit pupil plane of the photographic lens 1, and the imaging lenses 4a and 4b have a Pa ,
It is almost imaged as Pb. If the field lens 3 is not used, the secondary image formed when a uniform brightness surface is imaged will not have uniform brightness on the sensors 5a and 5b, resulting in so-called shading, which is undesirable.
Even when the above-mentioned shading is optically removed by using the above-mentioned shading, it has been found that the sensitivity changes depending on the angle of incidence of the imaging light beam on the sensor 5 as shown below. FIG. 2 depicts a graph in which the output from the sensor is normalized for each wavelength by the output at the time of vertical incidence, depending on the angle at which the imaging light beam is incident on the CCD sensor.

In this case, cases where normal incidence is 0 degrees and incident angles of 10 degrees and 20 degrees are shown, and it is clearly shown that the larger the incident angle is, the more pronounced the influence of wavelength becomes.

Returning to FIG. 1 again, the imaging points FO of the primary image on the optical axis 0 are points Fa and Fb on the respective sensors 5a and 5b.
Although the light is not incident perpendicularly to the sensors 5a and 5b, the absolute values of the incident angles are the same.

On the other hand, the imaging point FO' which is far from the optical axis O is imaged as points Fa' and Fb' on the respective sensors 5a and 5b, and the incident angle of the imaging light beam to the point Fa' is relatively The angle of incidence on Fb' is large, for example, 20 degrees, and the angle of incidence on Fb' is small, resulting in an unbalance of 1/1 of several degrees. Based on the graph of FIG. 2, it can be seen that the sensitivity differs by more than 20% depending on the wavelength. In this way, a phenomenon occurs in which the incident angle differs depending on the incident position of the imaging light beam, and a uniform brightness surface is no longer imaged as a uniform brightness surface, making it difficult to use the method of determining in-focus/out-of-focus based on the correlation between two images. Otherwise, it becomes a fatal flaw.

An object of the present invention is to eliminate the disadvantage of the conventional secondary imaging method in that the sensor output varies depending on the incident angle of the sensor array, as described above, and to make the imaging light beam incident on the sensor at an almost perpendicular angle. The object of the present invention is to provide a focusing state detection device that improves focusing accuracy by detecting an image formed by a first imaging system on a planned imaging plane or a plane conjugate thereto. In an apparatus that detects a focusing state based on the relative position of an image on each sensor in the sensor array direction, the image is guided onto at least two series of sensor arrays by a second imaging system. A correction optical system having positive power is disposed in front of the sensor to reduce the angle of incidence of the imaging light beam onto the sensor.

The present invention will be explained in detail based on the embodiments shown in FIGS. 3 and 4. Note that the same reference numerals as in FIG. 1 indicate the same members.

In the first embodiment shown in FIG. 3, a correction field lens 10a is provided immediately before each sensor 5a, 5b.
, 10b are arranged. The front focal point of one correction field lens tOa is the corresponding imaging lens 4.
For example, it exists at the rear principal point Ha of a.

The front focal point of the other correction field lens lob is also located at the rear principal point Hb of the corresponding imaging lens 4b. 11
12 is a diaphragm that determines the apertures of the imaging lenses 4a and 4b, and a field diaphragm that determines the field of view of the secondary imaging system.

Regarding the field lens 3, the aperture 11 and the pupil P of the first imaging system have a conjugate relationship, and the aperture 11 forms an image inside the pupil P.

Therefore, the light ray is emitted from the point FO that intersects the optical axis 0 on the planned imaging plane F of the photographing lens 1, and the secondary imaging lens 4a
The light ray ja passing through the principal point Ha will be perpendicularly incident on the surface of the sensor 5a after passing through the correction field lens 10a. Ray N emitted from the imaging point FO' outside the optical axis 0
Similarly, a' also passes through the correction field lens 10a and is incident perpendicularly onto the surface of the sensor 5a. The other secondary imaging system 4
Since the same effect applies to sensors 5a, 10b, and 5a, the outputs of these sensors 5a and 5b correspond to the characteristics shown by the dotted line when the incident angle is 0 degrees in FIG.

The uniform brightness surface will be output as a uniform brightness surface.

FIG. 4 shows a second embodiment, and in the embodiment of FIG. 3, each secondary imaging system has an individual correction field lens.
a and a fob, whereas in this embodiment, one correction field lens 1 having positive power is used.
What was done in step 3 and this correction field lens 13
The difference is that, for example, an adhesive layer 14 transparent to the imaging light beam is interposed between the sensor 5a and the sensor 5b.

With the configuration shown in FIG. 4, the adhesive layer 14 has the effect of alleviating the phenomenon shown in FIG. 2, and for example, even if the incident angle is 20 degrees, the change is only about 10 degrees. It turns out. In such a case, the chief ray j! emitted from each image point FO1FO' a, Ja' do not necessarily have to become parallel light to the elm that has passed through this correction field lens 13, and the incident angle θQ of the light ray jo when there is no field lens effect is the second due to the embedding effect of the adhesive layer 14. In the graph shown in the figure, the angle of incidence that does not matter much, for example, θI
According to experiments, if the angle of incidence θ to the sensor 5a is about 15 degrees, adhesive should be used between the correction field lens 13 and the sensor 5. It was confirmed that the variation in sensitivity corresponding to FIG. 2 when the layer 14 was embedded was suppressed to a width of 5%.

Various adhesives can be used as the transparent adhesive layer 14 in FIG. 4, and in some cases, a liquid may be used.

The configuration of the present invention can be implemented in all secondary imaging type focusing state detection devices, and can be modified in many ways, and is not necessarily limited to the optical system shown in the above-mentioned embodiments. , the secondary imaging system is not limited to the transmission type as in the embodiment,
Of course, it may also be of a reflective type.

As explained in detail above, according to the focused S detection device according to the present invention, when a CCD line sensor or the like of several tens to 100 pixels is used for image detection, it is possible to reduce the incident angle of the imaging light beam. By installing a correction optical system, the difference in output due to the difference in the angle of incidence of the light beam incident on each position on the sensor is alleviated, and erroneous signals are prevented when using various algorithms that correlate the two images. It is possible to accurately determine the focus without causing any problems. In particular, when it is necessary to save space, such as with an eye reflex camera, it is required that the imaging magnification of the secondary imaging system be 1 or less, preferably about 0.5. As the image plane, the secondary imaging lens, and the secondary imaging surface approach each other, the amount of change in the angle of incidence of each imaging light beam incident on each position on the sensor surface becomes large, so that the apparatus according to the present invention can be used extremely effectively. You can use it.

[Brief explanation of the drawing]

Fig. 1 shows the optical system of a conventional secondary imaging type focusing state detection device, Fig. 2 shows a characteristic diagram showing the relationship between the incident angle of the light beam on the sensor and the output, and Figs. 3 and 1@4 show the present invention. FIG. 2 is a configuration diagram of an embodiment of a focusing state detection device according to the present invention. 1 is a photographic lens, 3 is a field lens, 4a, 4
b is secondary image formation L/7z, 5.5a, 5b are sensors, lO
a, lOb, 13 are correction field lenses, and 14 is an adhesive layer. Patent applicant Canon Co., Ltd.

Claims (1)

[Claims] 1. An image formed by a first imaging system on a predetermined imaging plane or a plane conjugate thereto is guided by a second imaging system onto at least two series of sensor arrays; In a device that detects the focusing state based on the relative position of the image on each sensor in the sensor arrangement direction, a A focusing state detection device characterized by disposing a correction optical system having positive power. 2. The correction optical system is a field lens, and this field lens is provided for each second imaging system, and each focal plane is an exit pupil of the respective second imaging system. The focusing state detection device according to item 1. 3. The focusing state detection device according to claim 1, wherein the correction optical system is a field lens, and a filling layer transparent to the imaging light beam is interposed between the field lens and the sensor.