JPS58174912A - Focusing detector - Google Patents

Abstract

PURPOSE:To enable exact focusing discrimination by adhering an optical transparent medium which consists of a solid or liquid and is thicker than wavelength on the surface of each line sensor so as to decrease the reflection at the boundary surface. CONSTITUTION:The image by a photographic lens formed on an intended image plane is formed on two pieces of line sensors 4 by a pair of imaging lenses provided behind the intended image plane, and focusing is discriminated by the output signals of the two images obtained from these sensors 4. Each line sensor 4 is formed by providing many pieces of photoelectric conversion parts 11, which are called ''photosites'', on a silicon substrate 10, covering a thin film 12 consisting of silicon on the top layer thereof, further adhering a transparent medium 13 having a high refractive index which is thoroughly thicker than wavelength onto the front surface thereof and protecting the same with a protective glass plate 14. The reflected light which is generated on the surface of the film 12 is thus decreased considerably and the exact discrimination of focusing is made possible.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a focus detection device using a line sensor composed of a solid-state image sensor such as COD 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. Behind the photographic lens l, near the planned imaging plane, there is a photographic lens l.
and a field lens 2 whose optical axis 0 is the same, and behind the field lens 2, a pair of secondary imaging lenses 3a and 3b are arranged in parallel perpendicularly to the optical axis 0, and further behind each Light-receiving line sensors 4a and 4b, which are one-dimensional solid-state imaging devices such as COD, are arranged. 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.

An image is formed by the field lens 2 in the vicinity of the pupil +1 imaging lenses 3a and 3b of the photographing lens l, and furthermore, by these secondary imaging lenses 3a and 3b, the image I in the ranging field mask 5 has a light gravity of La, By calculating the correlation between the image signals that enter the line sensors 4a, 4b as Lb and are output from the line sensors 4a, 4b, the in-focus state of the image on the planned imaging plane is determined.

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 angle of incidence of incident light 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 O0) is taken as a reference of 1.0, the output level will fluctuate when the angle of incidence to the line sensor is 100.20°. 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 Figure 1, the angle of incidence of the principal ray from the secondary imaging lens 3a onto the line sensor 4a is determined by the incident position number corresponding to the image height. Line sensor 4a
There is a problem in that the output from is not output as a faithful image word.

Furthermore, the angle of incidence of these principal rays is determined by the line sensors 4a, 4.
Since it is asymmetrical with respect to the secondary image formed on b, the degree of correlation of the image output signal, which is the basis for determining focus, is low. In other words, the light ray L to the head of the arrow in the image
Comparing a' and Lt+'.

The incident angle of Lb' is large, and the incident angle of La' is small. Therefore, the output signal number from this part of the image (at X, the line sensor 4b outputs a large distortion L and a strong However, there is a drawback that the correlation between the two Φ signal outputs from the same and corresponding parts of the image cannot be correctly established, resulting in insufficient focus determination performance.

Such a problem becomes particularly noticeable in a compact focus detection device in which the distances between the field lens 2, the secondary imaging lenses 3a and 3b, and the line sensors 4a and 4b must be configured to be small.

In such a compact optical system, the pupil image of the photographing lens l formed by the field lens 2 becomes smaller and smaller.
The opening 6 becomes smaller accordingly. For this reason, the principal rays start to head towards the line sensors 4a, 4b from near the optical axis 0, and in particular the inclination of the rays of light incident on the ends of the line sensors 4a, 4b corresponding to the rays La', Lb' becomes large.
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. An image formed on the plane by the photographing lens is focused on two line sensor kings by a pair of imaging lenses provided behind the planned image forming plane, 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 is coated. This silicon substrate 10, photoelectric conversion section 11, thin film 1
2 is the same as the conventional line sensor 4, but in this embodiment, a transparent medium 13 with a high refractive index N and a thickness d sufficiently large compared to the wavelength is closely attached to the front surface of the thin film 12, and a protective glass is used. It is interposed between the plate 14 and the plate 14. thin film 1
When the refractive index of 2 is n, n −1> I N −n
1, the amount of reflected light generated on the surface of the thin film 12 can be greatly reduced, and the characteristics that were clearly shown in FIG. 2 can be improved.

FIG. 4 shows that the refractive index N=
1.56 ultraviolet curable adhesive as a high refractive transparent medium 13
This is the result of measurement in the same manner as in FIG. 2, with a uniform thickness of about 2 mm. Comparing this figure 4 with figure 2, we get
It can be seen that the degree of improvement is extremely large. The preferred high refractive index transparent medium 13 is (1) close to the refractive index n of the thin film 12, (2) preferably an adhesive for holding the protective glass plate 14, and (3) an IC package. Put the line sensor 4 inside, and put the medium 1 on top of it.
3 is preferably satisfied, it is desirable that the medium 13 be a liquid with low viscosity at the time of filling so that unnecessary air layers and bubbles do not remain. And (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 focus detection device with higher performance can be realized. becomes. Furthermore, when the line sensor 4 having such a structure is used, the output distortion from the line sensor 4 is reduced even for an incident light beam that is inclined to a certain degree, so that 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 required.

Further, in this case, the transparent medium 13 having infrared absorbing property is I
Since it is sealed within the C 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. In front of the line sensors 4a, 4b, a correction field lens 15 is provided with an appropriate interval, and a transparent medium 13 is inserted between them. 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 immediately before the line sensor 4.
is provided to reduce the angle of incidence of the light rays from the secondary imaging lenses 3a, 3b onto the line sensors 4a, 4b. Alternatively, a protective glass plate 14 may be disposed on the transparent medium 13 of the line sensors 4a, 4b-, and the correction field lens 15 may be bonded together with the protective glass plate 14.

As explained below, the focus detection device according to the present invention eliminates the interference effect due to the thin film on the surface of the line sensor by sealing the line sensor with a high refractive index transparent medium that has a sufficient thickness compared to the wavelength. can be reduced, and unevenness in spectral sensitivity of the line sensor due to the angle of incidence of the light beam can be reduced.

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 sectional view of the line sensor, the fourth line is a characteristic graph of the line sensor, and FIG. 5 is a configuration diagram of the focus detection device. 1 is a photographic lens, 2 is a field lens, 3a, 3
b is a secondary imaging lens, 4.4a and 4b are line sensors,
IO 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 lens. Patent applicant Canon Corporation $1321 4 114 Figure 400 500 6 (Re 1 Reno nm Figure 5

Claims (1)

[Claims] 1. An image formed on a planned imaging plane by a photographic lens,
A pair of imaging lenses provided behind the planned imaging plane forms an image on two line sensors, and a focusing state is determined based on image output signals of the two images obtained from these line sensors. A focus detection device characterized in that an optically transparent medium made of solid or liquid and thicker than the wavelength is brought into close contact with the surface of a line sensor to reduce reflection at the 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>I N -n I, where n is the refractive index of the thin film and N is the refractive index of the transparent medium.