JPS6169012A - Image pickup device with ttl focus detector - Google Patents

Abstract

PURPOSE:To simplify the structure by arranging dispersedly many minute reflecting or light-transmissive faces on the split surface of a beam splitter which leads a luminous flux to a focus detector. CONSTITUTION:A luminous flux L1 from an object passes a focusing system 1, a magnification varying system 2, a correcting system 3, and the first group 4a of a master system and is divided by a beam splitter 5, and one luminous flux L2 reaches a solid-state image pickup element 7 provided with a mosaic filter through the second group 4b of the master system, and the other luminous flux L3 reaches a focus detecting element 9 through a focusing system 8 for focus detection. Many minute reflecting faces 20 are provided on a beam split surface 5a of the beam splitter 5, and the luminous flux L3 to the focus detecting element 9 is obtained by them, and the luminous flux L2 to the solid-state image pickup element 7 is obtained by a light-transmissive part 21.

Description

[Detailed Description of the Invention] (Technical Field of the Invention) The present invention focuses a part of a light beam that passes through a part of an imaging optical system and is directed to an imaging element onto a one-dimensional or two-dimensional photoelectric conversion element array to detect a focus. The present invention relates to an imaging device having a TTL focus detection device that performs.

・(Background of the Invention) In an imaging device that obtains an image signal by photoelectrically converting an optical image of a subject using a surface sensor such as a picture tube or a solid-state image sensor, discrete photoelectric conversion is performed in at least one direction of the imaging surface. A conversion takes place. In other words, in the case of an image pickup tube, the horizontal direction of the image pickup surface is analog, but in the vertical direction, it is discrete photoelectric conversion using a finite number of horizontal scanning lines, and in the case of a solid-state image sensor, the photoelectric conversion section is discrete. Because they are two-dimensionally arranged, photoelectric conversion is discrete both in the horizontal and vertical directions of the imaging plane.

In addition, in an imaging device that uses a single image pickup tube or solid-state image sensor (hereinafter simply referred to as an image sensor), a color separation filter such as a stripe filter or a mosaic filter is attached to the image pickup surface. Discrete photoelectric conversion is performed.

It is generally well known that when photoelectrically converting a subject light image in a discrete manner as described above, it is necessary to cut off the high spatial frequency components of the subject light image based on the sampling theorem. Conventionally, therefore, a crystal filter, which is a spatial low-pass filter, was attached to the imaging surface of the image sensor.

For example, in an imaging device that obtains a color image signal using a single imaging element, spatial frequency components exceeding a certain value determined by the pattern pitch of a so-called color separation filter such as a stripe filter or a mosaic filter provided on the imaging surface are A cut-off crystal filter is provided near the imaging surface. Furthermore, even in an imaging device that uses three solid-state imaging devices (three-plate type), photoelectric sensors are originally discretely arranged two-dimensionally on the imaging surface of each solid-state imaging device.
It is necessary to take measures to cut spatial frequency components above a certain frequency determined by the pitch of the pattern of the converter. However, no countermeasures have been taken for the current three-panel imaging device.

In addition, even with a black and white video camera using an image pickup tube or a three-tube color video camera, it is necessary to cut out a certain frequency or more of the spatial frequency component in the vertical direction determined by the number of horizontal scanning lines, but in reality. No countermeasures have been taken.

On the other hand, a part of the light beam that passes through a part of the imaging optical system and reaches the image sensor is guided to a one-dimensional or two-dimensional photoelectric conversion element array for focus detection, and a subject image is formed on this to detect the focus.
TL focus detection device For example, a phase method that detects the phase difference between the outputs from two line sensors and controls it to O, or a method that compares the sum of the difference outputs between each photoelectric conversion element of the two line sensors. Even in the contrast method, etc., in which the image is controlled to be zero, since the optical image is photoelectrically converted in a discrete manner, there are restrictions on the high range of the spatial frequency components of the subject image due to the sampling theorem. For this reason, various people 1. ) method, that is, a spatial low-pass filter function that cuts high frequencies of the spatial frequency components of the subject light image or image signal using an optical filter or signal processing. It becomes necessary to provide a spatial low-pass filter on both of the detection photoelectric conversion elements.

Generally, the spatial frequencies to be cut by the image sensor and the photoelectric conversion element for focus detection are not the same (usually the spatial low-pass filter of the image sensor needs to pass higher frequencies). be.

Generally speaking, the pitch of color separation filters such as stripe filters and mosaic filters, which determine the properties of the spatial low-pass filter on the image sensor side, and the arrangement pitch of the photoelectric conversion section of the image sensor are better than the photoelectric conversion element array for focus detection. This is due to the fact that the pitch is finer than the arrangement pitch of the photoelectric conversion units.

Therefore, if the above-mentioned conditions change, the spatial frequency to be cut for the photoelectric conversion element for focus detection may be higher than that for the image sensor, or may be the same frequency.

(Object of the Invention) In view of the above, an object of the present invention is to simplify the structure by making the image pickup device and the focus detection photoelectric conversion device a single member without providing spatial low-pass filters for each.

(Summary of the Invention) The present invention consists of a beam splitting surface of a beam splitter used for guiding a light beam to a focus detection device, in which the entire surface is made up of a large number of regularly or irregularly shaped microscopic reflective surfaces or microscopic transparent parts. The beam splitter is formed by
The technical point is to provide the necessary spatial filter characteristics to each of the two luminous fluxes separated by.

(Example) FIG. 1 is a diagram showing an optical system of an example in which the present invention is applied to a four-group zoom lens. 1 is a focusing system, 2 is a variable power system, 3 is a correction system, 4 is a master system, 4a is a master system first group, 4
b is the master system second group, 5 is the beam splitter, 16 is the aperture, 7 is the solid-state image sensor equipped with a mosaic filter,
8 is a focus detection imaging system, and 9 is a focus detection element, which is a photoelectric conversion element array in which photoelectric conversion elements are arranged one-dimensionally.

L, is the light flux from the subject, and L2 is the beam splitter 5
One of the luminous fluxes separated by , reaches the solid-state image sensor 7 . L is the other beam split by the beam splitter 5 and reaches the focus detection element 9. The luminous flux L l, L
t and L- are represented by a ray passing through the optical center.

2 and 3 are diagrams showing the state of the minute reflection surface provided on the beam splitting surface 5a of the beam splitter 5. Reference numeral 20.30 is the minute reflection surface, which directs the light beam to the focus detection element 9. , is obtained. 21. 31 is a light-transmitting part, and the light beam passing through this part is the light flux L2 to the solid-state image sensor 7.
is obtained.

In the embodiment shown in FIG. 2, circular minute reflecting surfaces 2o are randomly arranged, and the luminous fluxes L v and L s have the desired intensity depending on the radius of the minute reflecting surfaces 20 and the interval between the minute reflecting surfaces 20. Spatial frequency limitation, ie, cutting of high frequencies, is achieved. In this case, high spatial frequencies in all directions of the object are uniformly limited.

Incidentally, contrary to the embodiment shown in FIG. 2, the transmitting surface may be a circular minute light transmitting surface, and the other portion may be a reflecting surface. Further, the minute reflective surface or the minute transparent surface does not necessarily have to be circular, but may have any shape.

In the embodiment shown in FIG. 3, thin line-shaped minute reflection surfaces are arranged in a stripe shape at regular intervals, and by appropriately selecting the width and interval of the thin line-shaped minute reflection surfaces, the luminous flux L2, Desired spatial frequency limiting characteristics can be obtained in each case. Note that in this example, there is no spatial frequency limiting characteristic in the horizontal direction (longitudinal direction of the thin line-like minute reflective surface), and the spatial frequency limiting characteristic appears only in the vertical direction. It can be applied to the removal of spatial frequency components determined by a finite number of horizontal scanning lines in video cameras, three-tube color video cameras, and the like.

Next, a more specific embodiment of the present invention will be shown together with numerical values. As a photoelectric conversion element array for focus detection, TCL (f″nrough The (:ame
ralens autofocus 3system)
, the focal length of the second group of the master system /'q26mm, the focal length of the focus detection imaging system 8 ! =; 52 dishes, pattern pitch of stripe filter of image sensor approximately 3011m
, the photoelectric conversion part arrangement pitch of the TCL is 0.1875 m
This is an example in which good results were obtained when using a lens array of 24 lenses lined up within a length of 4.5 mm, and the beam split surface 5a was as shown in FIG. It becomes. FIG. 4 is a diagram of the beam splitter 5 viewed from the direction of incident light, and the beam splitter surface 5a is set to be inclined at an angle of 4 with respect to the incident optical axis. Dimensions) are A=26mm
, B = 25.74 mmc is the region where the random pattern of aluminum dots is deposited, and the short axis DL =,
16.7mm, major axis E=23.6mm, and the number of dots in this area is 4,400. Dot diameter maximum 207μm,
It is a random pattern with a minimum of 185 μm and an average of 195 μm.

Incidentally, the subject light flux is configured to pass through an area slightly wider than the area C, and the ratio of passage (T) and reflection (R) of the light flux is T=70% and R: 3096.

(Effects of the Invention) As explained above, according to the present invention, the splitting surface of the beam splitter is made of a discrete arrangement of reflecting or transparent surfaces with a large number of minute shapes, so that each of the split luminous flux has a desired spatial frequency. A single member can provide high-frequency removal characteristics, and for this reason, spatial frequency limiting means for focus detection photoelectric element arrays, such as optical filters, high-frequency cut filters inserted in signal systems, and spatial frequency limiting of image pickup devices. It is not necessary to provide each means, for example, a crystal filter, and the structure becomes simple.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an optical system according to an embodiment of the present invention, FIGS. 2 and 3 are diagrams showing the state of a beam split surface according to an embodiment of the present invention, and FIG. 4 is a diagram showing a beam split surface according to an embodiment. FIG. (Explanation of symbols of main parts) 5... Beam splitter-15a... Beam split surface,

Claims (1)

[Scope of Claims] 1) An imaging device, an imaging optical system that forms a subject image on the imaging device, and a beam splitter that splits into two a luminous flux of the subject image that has passed through a part of the imaging optical system. , an imaging device comprising a TTL focus detection device that guides one of the light beams split by the beam splitter to a focus detection photoelectric conversion element array including a plurality of photoelectric conversion units arranged to form a subject image. . An imaging device having a TTL focus detection device, characterized in that the split surface of the beam splitter is constituted by a discrete arrangement of a large number of microscopic reflecting surfaces or transparent surfaces. 2) The TTL according to claim 1, wherein the micro-shaped reflective surface or transparent surface has a substantially circular shape.
An imaging device having a focus detection device. 3) An imaging device having a TTL focus detection device according to claim 1, wherein the microscopic reflecting surface has a thin line shape.