JPH01120519A - Focus detecting device - Google Patents

Abstract

PURPOSE:To detect the focusing of an objective lens by providing a mask, a field lens, an image re-forming means and a photoelectric conversion means, setting the opening of the mask in a desired way and correcting the difference of the ways that luminous fluxes passing through the opening are image-formed differently by means of the field lens. CONSTITUTION:The field lens 50 is arranged near the expected image forming surface of the objective lens and adjacent to the mask 42 opened in parallel. A light quantity distribution based on images of an object is created, and the relative positions of the object vary according to the way that the field lens 50 and the objective lens are focused through image re-forming lenses 51 and 52. Plural photoelectric conversion element columns 55 receive said distribution. The arranging direction of the opening of the mask 42 is optically orthogonal with that of image elements, and one side of the opening is set so that it is close to the distribution. Ultimately, the field lens 50 corrects the difference between a formed image appearing in a luminous flux passing through the opening close to the optical axis of the objective lens and a formed image appearing in a luminous flux passing through the opening farther the optical axis. Under this constitution, the detecting accuracy of a focus in the central part of a range finding visual field is kept high the same as in its outside, and a multipointed range can be found.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a focus detection device, and more particularly to a device for detecting the focus adjustment state of an objective lens.

[Conventional technology]

It is common for photo cameras or video cameras to have a built-in detection device for automatic focus adjustment. However, the distance measurement range is determined at the center of the viewfinder. A camera that focuses on a subject at a desired position within the viewfinder screen has not yet been realized.

In other words, if the distance measurement field of view is set at the center of the screen, there will be no problem if the main part of the subject is located at the center of the screen, but if it is off the center of the screen, erroneous distance measurement will occur and the focus will be incorrect. There is an inconvenience that the photo will be blurry. In order to solve this problem, we measured the distance by shaking the camera horizontally and placing the main part of the subject in the center of the screen, then returned the direction of the camera while maintaining the current focus adjustment state, and then released the shutter. Although it is possible to perform a release operation, it is cumbersome and may not be possible if you are in a hurry.

For example, it was difficult to respond to a request to take a photo in which a subject moving laterally was located off the center of the screen.

On the other hand, the imaging light flux from the objective lens is guided to a set of re-imaging lenses, the light intensity distribution formed by these lenses is received by the pixel array of the photoelectric conversion element, and the focus adjustment state of the objective lens is determined from the interval between both light intensity distributions. Devices for detection are well known.

As a method to satisfy the above-mentioned requirement to measure distance to objects located outside the center of the screen without shaking the camera, another pixel row is placed outside the pixel row placed on the optical axis. However, it is conceivable that the newly provided pixel row receives a subject image that is off the center of the screen.

[Problems to be solved by the present invention]

However, optical lenses generally have residual aberrations, and the imaging state of the light beam differs between positions near and far from the optical axis of the objective lens, making it difficult to perform accurate focus detection at positions far from the optical axis. It is.

It is an object of the present invention to solve the above-mentioned difficulties and provide a practical configuration that can actually perform distance measurement at multiple locations. and,
To achieve this purpose, a mask is placed near the intended image formation plane of the objective lens and has a plurality of apertures arranged in parallel, a field lens is placed adjacent to the mask, and a re-imaging means for forming a light quantity distribution based on an object image whose relative position changes; and a photoelectric conversion means having a plurality of sets of pixel rows receiving the light quantity distribution and converting the light quantity distribution into an electrical signal; The direction in which the apertures are arranged is optically orthogonal to the direction in which the pixel rows are arranged, one side of the aperture is set so that the light intensity distribution based on the object image approaches each other on the photoelectric conversion means, and In a field lens, the light flux passing through the aperture near the optical axis of the objective lens and the light are bent by a reflective surface, etc., so they are physically not perpendicular to each other. Also, light is not limited to only visible light.

〔Example〕

The focus detection device of the present invention can be used in single-lens reflex cameras that use silver halide film, -lens reflex electronic cameras, or video cameras, as well as in position detection devices for recording devices, processing machines, robot eyes, etc. .

FIG. 6 shows an example of the usage mode, and depicts the optical system of a -eye reflex camera, where 10 is a camera body and 20 is a detachable or replaceable lens barrel. 21 is an objective lens, and 1 is its optical axis. The optical axis 1 reaches a quick return mirror 22 with a semi-transparent region and is split into two parts. Along the inverted optical axis are a focusing screen 23, a pentaprism 24. An eyepiece lens 25 is provided to constitute a finder system for visual recognition.

A movable sub-mirror 26 and then a focus detection device 27 according to the present invention are arranged along the transmitted optical axis, and a driver (not shown) is operated by the output of the focus detection device 27, and the objective lens 2
1 position is adjusted. Incidentally, as is well known, the movable sub-mirror 26 is held by the quick return mirror 22.

A light source 28 such as an LED of an object illumination device illuminates a projection chart 29 on which a projection pattern is formed, and transmitted light is projected by a projection lens 30.

Hereinafter, the configuration of the focus detection device shown at 27 will be explained using FIGS. 1 to 3. FIG. 1 shows a perspective view, FIG. 2 shows a vertical cross-sectional shape, and FIG. 3 shows a positional relationship between a pixel row and a light amount distribution of a photoelectric conversion device consisting of a single chip. 42
is a multi-hole field mask, which in the figure has long sides in the horizontal direction and has rectangular apertures arranged in parallel; for example, the objective lens 21 in FIG.
is placed near the planned imaging plane. 43 is a filter that blocks light with wavelengths longer than near-infrared light. Reference numeral 50 denotes a split field lens, which is arranged slightly offset from the intended image formation plane of the objective lens. The divided field lens 50 includes lens parts 50a, 50b, 50c, 50d, which have different optical functions as described later.
50e.

50f and 50g, and these parts are formed by changing either or both of the lens thickness and the radius of curvature of the lens surface. Furthermore, instead of the split field lens 50, a combination of a Fresnel lens-like optical system in which different prisms are arranged for each aperture of the multi-hole field mask and a biconvex lens can be used.

51 and 53 form a re-imaging lens unit with a two-hole diaphragm 52 in between, and the convex lens 5 converts the incident light into a state close to parallel light.The optical function is described in Japanese Patent Publication No. 62-33564) , and a two-image forming lens 53 formed by joining two convex lenses 53a and 53b side by side forms two secondary images of the object image formed by the objective lens. The aforementioned two-hole aperture 5
2 denotes vertically long elliptical openings 52a arranged in the horizontal direction in the drawing.
, 52b.

54 is a concave lens for field curvature correction, and is arranged on a transparent plastic package 56 that houses a photoelectric conversion device 55 (FIGS. 2 and 3).

In addition, the split field lens 50. Although the convex lens 51 and the concave lens 54 of the re-imaging lens unit are shaped vertically, both are rotationally symmetrical spherical lens systems.

The light flux passing through the apertures 42...42g of the multi-hole field mask 42 is divided into divided fields L/:/S 5 as shown in FIG.
0 (DLz unit 50a, 50b, 50c
.

50d, 50e, and 50f-50g to form secondary images of the object on the photoelectric conversion device, respectively. Figure 3 shows this situation: 60a and 60b,...60m
and 60n, and 62a and 62b are a set of pixel columns consisting of a large number of pixels, 62a.

A filter having a bandpass characteristic approximately equal to the emission wavelength of an object illumination device to be described later is formed on the filter 62b. The aperture 4 of the multi-hole field mask corresponds to these pixel columns.
Images 61a...61n of 2a...42g are projected,
A secondary image of the object is formed inside this. At that time, the width of each aperture of the multi-hole field mask 42 and the light-shielding zone 42h between each aperture are determined.
...The mask 42 and the device 5 are arranged in accordance with the width of 42 m, the width of the pixel rows on the photoelectric conversion device 55, and the pitch of the pixel rows.
5, the refractive power of each lens part of the split field lens and the re-imaging lens unit is adjusted, so the light-shielding bands 42h...42m of the multi-hole field mask each emit light through a predetermined aperture. This prevents a part of the light flux from entering pixel columns other than the pixel column corresponding one-to-one with this aperture. Further, the field mask image includes the aperture apertures 52a, 52
b and lens portions 53a and 53b, two secondary images of the object inside are formed in each opening of the multi-hole field mask 42 in a row in the lateral direction, and the secondary images of the object therein are formed in relation to the position of the object image with respect to the intended imaging plane. moves in the directions of arrows A and B. Therefore, since each set of pixel rows detects the relative interval of the light intensity distribution regarding the paired secondary images based on the photoelectric conversion output, it is possible to know the focus state of the objective lens for multiple distance measurement positions. .

In addition, the pixel row is shaped to match the distortion of the visual field mask image,
It is desirable that the moving direction of the secondary image and the pixel column direction be configured to completely match. Further, each pixel column is separated to form a set, but a set may be created by allocating two ranges of one pixel column.

The function of the split field lens will be explained next. For comparison, we will use a configuration (No. 7), we will first explain the effect.

Point P on the optical axis within the distance measurement field of view and point Q outside the optical axis within the distance measurement field of view
Both are on the expected image formation plane, and the state of the light flux when these are projected onto the photoelectric conversion device 55 through the field mask aperture 100a is as shown in FIG. 112 in the diagram
and 113 are light rays emitted from points P and Q, respectively, and their imaging points are point R on the photoelectric conversion element and point S inside the concave lens 54. - When this focus detection device is applied to an eye reflex camera, the distance between points P and Q is 6 to 15
(mm), and furthermore, the distance from point P to the photoelectric conversion element is limited to 20 to 35 [mm], so even if the concave lens 54 for field curvature correction is used, the range of 2 The deviation of the next image plane cannot be resolved. As a result, focus and detection accuracy vary greatly depending on the distance measurement field of view, which is undesirable.

On the other hand, with a simple field lens configuration, it is extremely difficult to prevent the light beams passing through the distance measurement field near the optical axis l and the distance measurement field distant from the optical axis 1 from being eclipsed by the objective lens 21.

The vignetting of the light beam will be explained using FIG. 9. In the figure, 114 and 115 are images obtained by back projecting the two apertures of the two-hole diaphragm onto the exit pupil of the objective lens 21 through the field mask aperture 100a for each pixel column position; The light flux that has passed through the field mask aperture 100a passes through the aperture and reaches the photoelectric conversion device. Therefore, when the back projection areas 114 and 115 are off the exit pupil of the objective lens as shown in the figure, the AF light flux that should reach the photoelectric conversion element is vignetted by the objective lens, resulting in a significant decrease in focus detection accuracy. Otherwise, the focus becomes impossible to detect.

Since it is not possible to correct the above-mentioned difficulties in optical operation with a normal field lens, the light flux emitted from the outer aperture of the multi-hole field diaphragm and the light flux emitted from the aperture near the optical axis must be corrected using different field lenses. It can be corrected if

Next, the effects of the divided field lens according to the present invention will be explained using FIGS. 4 and 5. In Figure 4, a point T (Figure 2) within the distance measurement field on the optical axis on the planned imaging plane and a point U in the distance measurement field off the optical axis are photoelectrically converted through the field mask aperture 426.42g. 70 in the figure shows how it is projected onto the element.
71 is a ray of light emitted from point T, and 71 is a ray of light emitted from point U.

As shown in FIG. 2, the light ray 70 is transmitted through the central lens portion 50d of the field lens, while the light ray 71 is transmitted through the peripheral lens portions 50f and 50g. At this time,
These two lens parts are configured to align the image formation state on the photoelectric conversion device, and qualitatively, by increasing the lens thickness of 50f and 50g, which point is the image formation point of point 19 U? Points v and W also located on the photoelectric conversion device
becomes. As a result, it becomes possible to maintain uniformly high focus detection accuracy in each distance measurement field of view.

FIG. 5 shows an image obtained by back projecting the two apertures 52a and 52b of the diaphragm 52 onto the exit pupil of the objective lens through the endmost aperture 42a of the multi-hole field mask and the field mask aperture 42d on the optical axis. , 80a.

81a, 80b, and 81b are aperture apertures 52a, respectively.
, 52b (Fig. 1), and 80a, 81
b is what passes through the field mask aperture 42d, 81a, 8
1b is what passes through the field mask aperture 42a. As can be seen from the figure, by optimizing the field lens for each distance measurement field of view, it is possible to create a configuration in which the focus detection light beam is not eclipsed at any distance measurement field position. As a result, the distance measurement visual field position is not limited to the vicinity of the optical axis 1, but can be set over a wide range.

Incidentally, the light directed to the joint portions 50h to 50g of the field lens is through the light-shielding bands 42h and 42i of the field mask.

42j! , 42m to prevent the generation of ghost light due to light incident on this part.

Further, although the illustrated split field lens is made by integral molding of plastic, it is also possible to form each lens part individually and then combine them.

FIG. 10 shows the arrangement of the distance measurement field of view, and in accordance with the single-lens reflex camera shown in FIG. - 91g and 92 are laid out in parallel.

And the set of pixel columns 60a, 60b, . . . 60' in FIG.
If m.60n is back-projected onto the intended image forming plane using a solid imaging lens unit, and the distance measuring field of the focusing screen 23 is replaced on the intended image forming plane, the set of pixel rows and the distance measuring field will overlap with each other. become. This is a direction in which the arrangement direction of the set of pixel columns coincides with the intersecting direction of the plane including the camera body sub-mirror 26 (perpendicular to the drawing).

Adopting this arrangement has the advantage that the range from the distance measurement field of view at one end to the distance measurement field of view at the other end can be maximized without increasing the width of the movable submirror in the vertical direction.

The horizontal stripe pattern in FIG. 11 is an example of a projection pattern projected onto an object with low contrast or low brightness, and is depicted in chart 29 in FIG. 6. Assuming that this figure is a projected pattern image projected onto an object, reference numeral 93 indicates the distance measurement range when the set of pixel columns 62a and 62b in FIG. 3 is back-projected onto the object. As mentioned above, the pixel rows 62a and
A bandpass filter having a wavelength substantially equal to the emission wavelength of the illumination light source 28 (FIG. 6) is formed on the light source 62b.
The pixel array selects and senses the projected pattern reflected by the object. This forcibly adds contrast to objects that are normally difficult to detect, and enables focus detection using the pixel rows 62a and 62b. By the way, 94 is pixel row 60g/62
This is the distance measurement range on the object by h.

With the above configuration, the electrical signal from the photoelectric conversion device 56 (FIG. 1, etc.) is read out for each pixel column, and, for example, the in-focus state is calculated for each distance measurement field of view, and the continuity is verified. Various signal processing algorithms can be selected, such as selecting a nearby object within a highly continuous range, or selecting a predetermined distance measurement field of view in advance and focusing on an object that has entered that field.

〔Effect of the invention〕

According to the present invention described above, there is an effect that distance measurement can be performed at multiple positions including a distance measurement field of view located off the center.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing an embodiment of the present invention. FIG. 2 is an optical cross-sectional view. FIG. 3 is a front view of the photoelectric conversion device. FIG. 4 is an optical partial cross-sectional view. FIG. 5 is a perspective view. FIG. 6 is a sectional view of a configuration showing an example of application to a camera. FIG. 7 is an optical cross-sectional view for comparative explanation of effects. FIG. 8 is an optical partial cross-sectional view. FIG. 9 is a perspective view for comparative explanation of effects. FIG. 10 is a plan view of the observation field. FIG. 11 is a diagram showing the relationship between a projection pattern and a pixel row. In the figure, 42 is a multi-hole field mask, 50 is a split field lens, 50a...50g are lens parts, 51 is a convex lens of a re-imaging lens unit, 53 is a two-image forming lens, 52 is a two-hole aperture, and 55 is a photoelectric conversion device, 60a-60n,
62a and 62b are pixel columns. /l)σ f3

Claims (1)

[Claims] A device for detecting a focus adjustment state of an objective lens, comprising: a mask disposed near a planned imaging plane of the objective lens and having a plurality of apertures arranged in parallel; and a field lens disposed adjacent to the mask. It has a re-imaging means that forms a light intensity distribution based on an object image whose relative position changes according to the focus adjustment state of the objective lens, and a plurality of sets of pixel arrays that receive the light intensity distribution, and converts the light intensity distribution into an electrical signal. a photoelectric conversion means for converting the image, the direction in which the apertures are arranged is optically orthogonal to the direction in which the pixel rows are arranged, and one side of the aperture is such that a light amount distribution based on the object image approaches the object image on the photoelectric conversion means. The focus detection device is configured such that the field lens corrects a difference in imaging state between a light beam passing through an aperture near the optical axis of the objective lens and a light beam distant from the optical axis.