JPH0522219B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a focus detection device using a line sensor consisting of a solid-state imaging device such as a CCD or MOS.

FIG. 1 is a block diagram of a focus detection device used in a camera, etc., which is known as a so-called secondary imaging system. A field lens 2 having the same optical axis O as that of the photographing lens 1 is provided behind the photographing lens 1 in the vicinity of the planned imaging plane, and behind the field lens 2 a pair of secondary imaging lenses 3a, 3b are provided.
are arranged in parallel perpendicularly to the optical axis O, and light receiving line sensors 4a and 4b, each of which is a one-dimensional solid-state imaging device such as a CCD, are arranged behind these. Note that here, a distance measuring field mask 5 is arranged just in front of the field lens 2, and an aperture 6 is provided in front of the secondary imaging lenses 3a and 3b. The field lens 2 forms an image of the pupil of the photographing lens 1 in the vicinity of the imaging lenses 3a and 3b, and these secondary imaging lenses 3a and 3b form the image I in the ranging field mask 5 into luminous fluxes La and Lb. is incident on the line sensors 4a, 4b, and the line sensors 4a, 4b
The in-focus state of the image on the planned imaging plane is determined by calculating the correlation between the image signals output from the .

However, if a conventional line sensor is used in such a focus detection device, the following problems will occur. FIG. 2 is a graph showing how an interference phenomenon occurs depending on the incident angle of light incident on a conventional CCD line sensor, and how the output from the line sensor changes. In this graph, if the output from the line sensor at normal incidence (angle of incidence 0°) is taken as a reference of 1.0, the output level will fluctuate when the angle of incidence to the line sensor becomes 10° or 20°. Furthermore, it is shown that the degree of this change differs depending on the wavelength of the incident light.

When such line sensors are used as the line sensors 4a and 4b shown in FIG. 1, the angle of incidence of the principal ray from the secondary imaging lens 3a onto the line sensor 4a changes depending on the incident position corresponding to the image height. Therefore, there is a problem that the output from the line sensor 4a is not output as a faithful image signal.

Furthermore, since the incident angles of these principal rays are asymmetrical with respect to the secondary images formed on the line sensors 4a and 4b, the degree of correlation between the image output signals that are the basis for determining focus becomes low. In other words, if we compare the rays La' and Lb' to the head of the arrow in the image in Figure 1, we get
The incident angle of Lb' becomes large, and the incident angle of La' becomes small. Therefore, regarding the output signals from this part of the image, the line sensor 4b outputs a highly distorted signal, while the line sensor 4a outputs a relatively correct signal, so that the output signals correspond to the same location on the image. There is a drawback that the correlation between the two signal outputs from the parts cannot be correctly determined, resulting in insufficient focus determination performance.

Such a problem is caused by the field lens 2, the secondary imaging lenses 3a, 3b, and the line sensors 4a, 4b.
This is particularly noticeable in a compact focus detection device that must be constructed with a small distance between the two.
In such a compact optical system, the pupil image of the photographing lens 1 formed by the field lens 2 becomes smaller and smaller, and the aperture 6 becomes smaller accordingly. For this reason, the principal rays are directed toward the line sensors 4a and 4b from near the optical axis O, and especially the rays La',
The inclination of the light beam incident on the end portions of the line sensors 4a, 4b corresponding to Lb' becomes large, and the distortion of the output signals from the line sensors 4a, 4b becomes extremely large.

An object of the present invention is to provide a focus detection device that solves the problems of the conventional focus detection device as described above and enables accurate focus determination. The image formed by the photographing lens on the surface is formed on two line sensors by a pair of imaging lenses provided behind the planned image forming surface, and the two images obtained from these line sensors are In a focus detection device that determines the focus state based on an image output signal, an optically transparent medium made of solid or liquid and thicker than the wavelength is brought into close contact with the surface of the line sensor to reduce reflection at the interface. It is characterized by:

The present invention will be explained in detail based on the embodiment shown in FIG. 3 and below.

FIG. 3 is an enlarged cross-sectional view of a part of the line sensor 4 according to the embodiment. A thin film 12 consisting of the above is coated. This silicon substrate 10, photoelectric conversion section 11, and thin film 12 are similar to the conventional line sensor 4, but in this embodiment, a high refractive index N having a thickness d sufficiently large compared to the wavelength is provided on the front surface of the thin film 12. A transparent medium 13 is closely attached and interposed between the protective glass plate 14 and the protective glass plate 14 . When the refractive index of the thin film 12 is n, by setting n-1>|N-n|, the reflected light generated on the surface of the thin film 12 can be greatly reduced, which is noticeable in FIG. The properties shown can be improved.

In Figure 4, an ultraviolet curing adhesive with a refractive index of N = 1.56 is provided as a high refractive transparent medium 13 to a uniform thickness of about 2 mm on the thin film 12 of the line sensor 4, and measurements are taken in the same manner as in Figure 2. This is the result. Comparing this FIG. 4 with FIG. 2, it can be seen that the degree of improvement is extremely large. The preferred high refractive index transparent medium 13 is (1) a refractive index close to n of the thin film 12, and (2) preferably an adhesive for holding the protective glass plate 14. (3) It is preferable to put the line sensor 4 inside the IC package and fill the upper part with the medium 13. At this time, the medium 13 should be viscous to prevent unnecessary air layers and bubbles from remaining. It is desirable that the liquid be small in size. (4) After sealing the IC package with the protective glass plate 14, it is desirable to harden it to a certain degree, and for example, an ultraviolet curing type adhesive is suitable.

By using the line sensor 4 having such a structure in place of the conventional line sensors 4a and 4b shown in Fig. 1, the above-mentioned problems can be reduced and a higher performance focusing detection device can be realized. becomes. Furthermore,
If the line sensor 4 having such a structure is used, the line sensor 4 can be used even for incident light rays that are tilted to a certain degree.
Since the output distortion is reduced, a more compact focus detection device can be obtained.

Conventionally, a glass that absorbs or reflects infrared rays is provided elsewhere in the focus detection optical system to remove harmful infrared rays, but a transparent medium 13 with a high refractive index that includes an infrared absorber If this is used, the above-mentioned infrared absorbing glass etc. are not necessary. Furthermore, in this case, since the transparent medium 13 having infrared absorbing properties is sealed within the IC package, there is no need to consider the durability of infrared absorbing glass, which has been a problem in the past.

FIG. 5 shows another embodiment, in which the same reference numerals as in FIG. 1 indicate the same members. line sensor 4a,
4b, a correction field lens 15 is provided at an appropriate interval, and a transparent medium 13
is filled. Even if the line sensor 4 is sealed with a transparent medium 13 having a high refractive index, as shown in FIG. 4, it does not necessarily completely eliminate unevenness in spectral sensitivity due to oblique incidence. However, in this embodiment, a correction field lens 15 is provided just before the line sensor 4, and the secondary imaging lenses 3a, 3b
The incident angle of the light rays from the line sensors 4a and 4b to the line sensors 4a and 4b is made small. Alternatively, a protective glass plate 14 may be arranged on the upper layer of the transparent medium 13 on the line sensors 4a, 4b, and the correction field lens 15 may be bonded together with the protective glass plate 14.

As explained above, the focus detection device according to the present invention reduces the interference effect caused by the thin film on the surface of the line sensor by sealing the line sensor with a high refractive index transparent medium having a sufficient thickness compared to the wavelength. This makes it possible to reduce unevenness in the spectral sensitivity of the line sensor due to the angle of incidence of the light beam. Furthermore, the signal outputs of the two images have a high degree of correlation without distortion, making it possible to realize a focus detection device with higher performance. Furthermore, if a transparent adhesive is used as the high refractive index transparent medium used at this time, it is convenient for sealing the IC package.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of a conventional focus detection device, FIG. 2 is a characteristic graph of a conventional line sensor with respect to the angle of incidence, and FIG. The figure is a cross-sectional view of the line sensor.
FIG. 4 is a characteristic graph of the line sensor, and FIG. 5 is a configuration diagram of the focus detection device. Code 1 is a photographic lens, 2 is a field lens,
3a and 3b are secondary imaging lenses, 4, 4a and 4b are line sensors, 10 is a silicon substrate, 11 is a photoelectric conversion unit, 12 is a thin film, 13 is a transparent medium, 14 is a protective glass plate, and 15 is a correction field. It's a lens.

Claims (1)

[Scope of Claims] 1. An image formed by a photographing lens on a scheduled imaging plane is formed on two line sensors by a pair of imaging lenses provided behind the scheduled imaging plane, and these images are In a focus detection device that determines the focus state from the image output signals of two images obtained from a line sensor, an optically transparent medium made of solid or liquid and thicker than the wavelength is tightly attached to the surface of the line sensor. A focus detection device characterized by reducing reflection at an interface. 2. The focus detection device according to claim 1, wherein the transparent medium is filled between a thin film on the surface of the line sensor and a protective glass plate provided in front of the thin film. 3. The focus detection device according to claim 1, wherein a correction field lens for reducing the angle of incidence is disposed in front of the transparent medium. 4. The focus detection device according to claim 2, wherein n-1>|N-n|, where n is the refractive index of the thin film and N is the refractive index of the transparent medium.