JPH07104478B2 - Focus detection device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical device including a photoelectric element, and in particular, includes a focus detection device that prevents deterioration in accuracy due to undesired light.

BACKGROUND OF THE INVENTION Industrialized devices that are incorporated into cameras and detect the focus adjustment state of an objective lens are already well known. In particular, a plurality of parallel re-imaging lenses or a combination of image split prisms and re-imaging lenses are used to re-form a plurality of object images with parallax from the image of the objective lens. A phase difference detection method in which an image is received by a pixel array of photoelectric conversion elements and a focus adjustment state of an objective lens is detected is becoming mainstream.

On the other hand, in the focus detection device, in order to measure the wavelength at which the chromatic aberration of the objective lens is favorably corrected and to make it enter the photoelectric conversion element, a measure such as cutting a wavelength of 700 nm or more is taken. In order to cut the infrared region, a multilayer interference filter is often used, and most of the light that has not passed through the filter is reflected.

FIG. 4 shows an example of the filtering characteristic, but the characteristic curve in the wavelength cut region is slightly inclined.
50% of the light with a wavelength of 0 nm is transmitted and 50% is reflected.

By the way, when performing auto-focus shooting, the light from the scene sometimes contains a relatively strong light of about 700 nm, which is especially useful for low-brightness, low-contrast subjects. When performing supplementary illumination to do so, a commonly used illumination light source usually contains light with a wavelength of about 700 nm.

Occasionally, a detection error is confirmed when a subject is photographed under a specific environment, and it is considered that the cause is an undesired wavelength of light that has passed through the wavelength cut filter. That is, as described above, even if the wavelength cut filter is attached, some undesired light passes through the filter and is mainly reflected by a mask hung on a portion other than the pixel row of the photoelectric conversion element, For example, with respect to the re-imaging lens, it is reflected at the position optically conjugate with the photoelectric conversion element or the back surface of the filter arranged immediately before the photoelectric conversion element, and then enters the photoelectric conversion element again.
It is speculated that the light causes a ghost. The mask applied to the photoelectric conversion element is mostly made of aluminum with high reflectance, and the filter is placed at a position conjugate with the photoelectric conversion element or immediately before the position based on other optical requirements. However, even with other arrangements, it is difficult to avoid large or small ghosts.

FIG. 5 is a diagram showing the output of the photoelectric conversion element when the uniform luminance surface is projected by the objective lens 1, and the portions indicated by arrows A and B are the output due to the ghost.

When a ghost occurs in this way, a detection error occurs when detecting a relative positional deviation between two pixel column outputs, and accurate focus detection becomes impossible. A method of detecting the relative positional deviation is disclosed in Japanese Patent Laid-Open No. 142306/1983. In addition, the focus detection error due to this ghost appears remarkably when the transmittance of the infrared cut interference filter is about 20 to 80%, so when the object is illuminated with light with a wavelength of 700 nm as mentioned above. And so on.

Problems to be Solved by the Invention The present invention is to prevent a decrease in detection accuracy or an erroneous detection due to the ghost image.

Then, in order to achieve this object, photoelectric conversion means for outputting a signal relating to the focus adjustment state, optical means for guiding the object light to the photoelectric conversion means, and visible light by cutting the infrared wavelength region of the object light A device comprising a filtering means for transmitting light, wherein both surfaces of the filtering means and the photoelectric conversion means are configured to be in an optically non-parallel state. Here, “optically non-parallel” means that even if the optical axis is physically bent by a reflecting mirror or the like, it is not parallel when the optical axis is expanded.

Description of Embodiments An embodiment of the present invention will be described with reference to FIGS. 1 and 2.

In the figure, reference numeral 1 denotes a detachable objective lens for forming an object image on a predetermined image plane, which is adjusted by an adjusting device (not shown) driven by a detection signal. Reference numeral 2 denotes an optical splitter, and in the case of a single-lens reflex camera, a film or a video shooting element is arranged on the extension of the original optical axis X, and members described below are arranged on the branched optical axis. Here, the optical axis is shown expanded for convenience.

3 is a field mask, and 4 is a field lens, which is arranged on the planned image forming plane. Reference numeral 5 is a diaphragm, 6 is a secondary imaging lens, and 7 is a photoelectric conversion element having two pixel columns. The field mask 3 is located in the vicinity of the planned image plane of the objective lens 1 and has an opening 3a.
The object image formed by the objective lens 1 is re-formed on the photoelectric conversion element by the secondary imaging lens 6. At this time, since there are two lens portions 6a and 6b of the secondary imaging lens corresponding to the two openings 5a and 5b of the diaphragm 5, the secondary image divided into two is formed on the photoelectric conversion element. It is formed. Further, since the diaphragm 5 and the exit pupil of the objective lens 1 are in a conjugate relationship by the field lens 4, the secondary image projected on the photoelectric conversion element surface is formed by the light flux passing through different regions of the objective lens 1. Becomes Therefore, in the front focus state in which the object image by the objective lens 1 is formed on the objective lens rather than the planned image formation plane, the illuminance distribution in the field mask images 8a and 8b moves in the arrow direction, and the rear focus state. In, it moves in the direction opposite to the arrow.

Pixel columns 7a and 7b are located in the visual field mask images 8a and 8b, respectively, and the illuminance distribution of the subject image is extracted as an electric signal. The focus state of the objective lens can be known by detecting the relative positional deviation between the two images based on the output of this photoelectric conversion element.

Reference numeral 9 denotes a filter, which is formed by vapor-depositing a multilayer interference thin film that cuts an infrared wavelength region for spectral sensitivity correction on a light-transmissive flat plate. It is arranged to be inclined with respect to a plane perpendicular to the axis.

2A is a cross-sectional view of the focus detection device in the direction perpendicular to the pixel row, and FIG. 2B is a cross-sectional view orthogonal to FIG. As described in FIG. 2, the light rays reflected by the surface of the photoelectric conversion element 7 travel in the opposite direction through the secondary imaging lens 6b and the diaphragm aperture 5B, reach the infrared cut interference filter 9 and are condensed, but the filter is tilted. The reflected light does not enter the diaphragm aperture 5a again because it is arranged. Therefore, this stray light is generated by the photoelectric conversion element 7.
And does not affect the focus detection accuracy. FIG. 3 shows the output of the photoelectric conversion element when a uniform luminance surface is projected by the objective lens 1, and a uniform output can be obtained with only a drop in the peripheral light amount due to the characteristics of the optical system.

Although the cut wavelength changes by tilting the infrared cut interference filter, this can be dealt with by selecting the characteristics in consideration of the tilt angle. Further, in the above example, the filter is arranged at a position that is optically conjugate with the photoelectric conversion element,
The same problem can be solved even when it is arranged immediately before the photoelectric conversion element. On the other hand, instead of tilting the filter, it is also possible to tilt the surface of the mask to be applied to the photoelectric conversion element to divert undesired light, and in that case, the interference thin film can be provided on the surface of the field lens.

Further, the present invention can be applied not only to a single-lens reflex camera, but also to a video camera and the like, and can also be applied to an interval determining device of a processing machine.

EFFECTS OF THE INVENTION According to the present invention, focus detection can be performed regardless of the wavelength of light coming from the object field, and the annoyance of switching between manual operation and automatic operation in consideration of the detection environment is released, and it is also related to illumination light. There is no fear of malfunction.

Further, in particular, when auxiliary light is used for detection under low brightness, an easily available light emitting diode or small light bulb with an emission wavelength of about 700 nm can be used as a light source, so that the performance can be inexpensive and reliable. Even at times, there is an effect that a detection error does not occur.

[Brief description of drawings]

FIG. 1 is a perspective view showing an embodiment of the present invention, and FIG. 2 (A)
(B) is a cross-sectional view. FIG. 3 is a diagram showing the output of the photoelectric conversion element. Fig. 4 is a characteristic diagram of the filter. FIG. 5 is a diagram showing an output of the photoelectric conversion element when a ghost image is generated.

 ─────────────────────────────────────────────────── --- Continuation of the front page (72) Inventor Takeshi Koyama 770 Shimonoge, Takatsu-ku, Kawasaki-shi, Kanagawa Canon Inc. Tamagawa Plant (56) References JP-A-60-32013 (JP, A) JP-A-62 -34113 (JP, A)

Claims (6)

[Claims] 1. A photoelectric conversion unit that outputs a signal relating to a focus adjustment state, an optical unit that guides object light to the photoelectric conversion unit, and a filtering that cuts an infrared wavelength region of the object light and transmits visible light. A focus detection apparatus comprising a means, wherein both surfaces of the filtering means and the photoelectric conversion means are configured to be in an optically non-parallel state. 2. The filter according to claim 1, wherein the filtering means is arranged in the vicinity of the photoelectric conversion means or in a position optically conjugate with the photoelectric conversion means with respect to the optical means or in the vicinity thereof. Focus detection device. 3. The focus detection device according to claim 2, wherein the optical means forms a plurality of object images from object light. 4. The focus detection device according to claim 1, wherein said filtering means has a semi-transmission / semi-reflection characteristic for at least a specific wavelength. 5. The focus detection device according to claim 2, wherein the filtering means is a multilayer interference filter. 6. The focus detection device according to claim 1, wherein the photoelectric conversion means has a pixel column.