JPH05181056A - Focus detecting device - Google Patents

Abstract

PURPOSE:To obtain a focus detecting device capable of accurate focus detection by utilizing an image deviation system. CONSTITUTION:Plural light quantity distributions concerning an object image are formed on the surface of a light receiving means 34 by an optical means 31 by using a luminous flux which passes through plural areas where the pupil of a photographing lens 21 is different, and the relative positional relation of the plural light quantity distributions is obtained by the means 34, then the focusing state of the photographing lens is detected by using the signal from the means 34. In such a case, the optical means 31 is provided with plural progressive degree spectacle lenses 33 whose refracting force in its center part is weak and whose refracting force in its peripheral part is strong.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a focus detection device suitable for a photographic camera, a video camera, etc., and particularly, the pupil of a photographing lens (objective lens) is divided into a plurality of regions, for example, two regions, and each region is divided into two regions. Focus detection using a so-called image shift method that detects the in-focus state of the objective lens by forming a light amount distribution for two object images using the passing light flux and determining the relative positional relationship between these two light amount distributions. It relates to the device.

In addition, according to the present invention, a zoom lens is used as a photographing lens, and a lens group on the image plane side of the zooming portion is used when performing focus detection by an image shift method using a part of a light flux passing through the zoom lens. The present invention relates to a focus detection device suitable for a so-called rear-focus type zoom lens that performs focusing with the.

[0003]

2. Description of the Related Art Conventionally, there is a so-called image shift method as a light receiving type focus detection method using a light beam that has passed through an objective lens.

This image shift method is disclosed in, for example, Japanese Patent Laid-Open No. 59-10.
It is proposed in Japanese Laid-Open Patent Publication No. 7311 and Japanese Patent Laid-Open No. 59-107313.

FIG. 4 is a schematic view of an essential part of an optical system when an image shift type focus detection device is provided in a part of a zoom lens for a video camera or a still video camera.

In the figure, reference numeral 21 is a taking lens, which is composed of a zoom lens. Reference numeral 22 is a focus lens group, 23 is a variable power lens group for zooming (variator lens group), 24 is a correction lens group (compensator lens group) for correcting image plane variation due to zooming, and 25 is an afocal lens. It is a lens group, and the emitted light flux is made substantially parallel light.

Reference numeral 26 is a stop, 27 is a fixed lens group (master lens group) which is fixed during zooming, 28 is a low-pass filter, 29 is an image sensor, and 30 is an image plane.

In the figure, the afocal lens group 25
The deflecting means 32 (or a deflecting means comprising a prism having a half mirror surface inside) inclined by 45 degrees with respect to the optical axis for separating and deflecting the light flux by the focus detecting means is arranged between the aperture and the diaphragm 26. is doing. Then, through the infrared light cut filter 35, a secondary optical system 33 including two separator lenses (secondary lenses) 33a and 33b uses light beams from different regions on the pupil plane of the taking lens 21 to obtain two subject images. A light receiving means 34 including two sensor arrays (light receiving element rows) 34a and 34b.
It is formed on the surface.

The reference numeral 37 designates a visual field mask, which is disposed either before or after the separator lenses 33a and 33b.
When capturing one subject image, the two subject images are separated.

In the figure, the light quantity distributions relating to two identical subject images are respectively obtained by using the light fluxes passing through the two regions of the objective lens having different pupils by the secondary optical system.
It is formed on a and 34b. At this time, the relative positional relationship between the two light amount distributions formed on the light receiving element array surface, that is, the amount of deviation of the light amount distributions differs depending on the focus state of the focus lens group 22. For example, the light receiving element rows 34a, 34
In the arrangement direction of the elements on b, a lateral shift amount appears according to the amount of defocus of the focus lens group 22 from the planned image forming surface.

The detection of the focus state of the focus lens group 22, that is, the detection of the out-of-focus amount, the relative positional relationship between the two light amount distributions at this time, that is, the lateral deviation amount of the light amount distribution is detected by the light receiving means 34 and calculated. It is done by processing.

Generally, at this time, the two light receiving element arrays 34
The relative lateral shift amount δ of the light amount distributions on a and 34b and the defocus amount d of the objective lens have a constant function relationship.

For example, if a single evaluation scale is calculated using the signal value obtained by the light receiving means 34, it can be determined that the object is in focus. A typical example of the single evaluation scale here is a cell (light receiving element) corresponding to each of a pair of sensor arrays.
Focusing is performed when the sum of the absolute values of the A / D converted values of is the minimum value.

FIG. 5 is an explanatory diagram schematically showing the meaning of the single evaluation scale.

Now, considering only the sensor array 34a on one side, if the cell pitch is Pa and the number of cells (the number of light receiving elements) is Na, the sensor length (light receiving element row length) La is Na × Pa.
Becomes The above-mentioned sensor length with respect to the image pickup screen in consideration of the imaging magnification is approximately the distance measuring field length, but this is not necessarily wide, and there is an optimum value, which is usually about 30 to 40%.

However, in the so-called large blurring state where the defocus amount is extremely large, it is advantageous that the sensor length is long as the so-called prediction precision for instantaneously obtaining the direction to the in-focus position and the shift amount.

In view of the above contradictory matters, a single evaluation scale is usually obtained as follows. That is, the photoelectric conversion value is the number of cells Na
However, in the case of correlation, only about half of Na / 2 is focused, and hereinafter this is named a window.

Next, the left and right sensor arrays 34a, 34b
The window of is gradually shifted by a shift register to obtain a single evaluation scale at each time. This allows a single metric to be plotted against a window shift.

However, when the single evaluation scale cannot take the minimum value with the preset shift amount, the focusing lens unit is not in the in-focus position, that is, it is in the defocus state, and focusing is performed based on this information. Move the lens group.

In FIG. 5, as the focusing lens group 22 approaches the in-focus state, the subject image 41a on the sensor array 34a and the subject image 4 on the sensor array 34b.
When 1b overlaps, the absolute value of the difference between the paired cells is ideally zero at the time of focusing, and the single evaluation scale obtained by summing them is also ideally zero.

In the above process, when a single evaluation scale is plotted against the shift of the window, it is necessary to interpolate between the shifts of one cell and electrically obtain it in order to improve the accuracy. Let this be the number N of effective interpolations.

The focal length of the master lens is f _M , and the afocal magnification at the telephoto end (the ratio of the height of the parallel light incident on the focus lens group 22 to the height of the parallel light emitted from the afocal lens group 25) is M _T , Where B is the baseline length between the optical axes of the separator lens 33 and f _S is the focal length of the separator lens 33, the following formula is established.

[0023]

[Equation 1] In the above equation, dZ is the focus resolution of the taking lens 21 in the optical axis direction, and the equation (1) is

[0024]

[Equation 2] The smaller the sensor pitch Pa, the longer the base line length B, the longer the focal length f _S of the separator lens 33, and the larger the value of the effective interpolation number N, the higher the focus shift detection capability of the taking lens 21.

On the other hand, the amount of prediction is Lmin when the closest distance at which focus can be detected is Lmin.

[0026]

[Equation 3] Becomes Here, Xmax is the maximum difference of the barycentric positions of the object images of both sensor arrays that can be detected, that is, the maximum value of the phase difference, and this value becomes large if the sensor length La is long.

As is clear from the comparison between the equations (2) and (3), if the prediction distance is made as short as possible, the parameters B and f _S become small, and the focus shift detection accuracy deteriorates. Further, f _M and M _T have a relationship of f _T = M _T · f _M (4), where f _T represents the focal length of the entire lens system at the telephoto end.

The advantages of both the amount of prediction and the ability to detect the focus shift are that the sensor length La is long, the effective interpolation number N is large, and, of course, the sensor pitch Pa is fine. ..

In addition to the focus detection method described above, a video camera, an electronic still camera or the like using a solid-state image pickup device or the like has conventionally been used to perform focus detection using an image pickup signal obtained from the image-forming light of a photographing lens. Are known.

The principle of operation is that high frequency components obtained from an image pickup device such as a solid-state image pickup device are extracted and the contrast thereof increases with focusing, and in general, the phase difference of a subject image is detected. It is called a blur detection method as opposed to the image shift method.

However, the blur detection method does not always include a high frequency component in a normal subject. For this reason, the detection frequency band is appropriately switched according to the zooming state and the degree of focusing, but basically it has a weak point that the focusing accuracy is poor for a low-contrast subject.

Further, in the blur detection method, it is difficult to specify the in-focus position from the blur state (prediction detection), the focus cannot be detected when the blur is large, and the focusing operation takes a long time due to the feedback operation. Have a point. The advantage of the above-described image shift detection method over this blur detection method is that the shift amount on the image plane can be obtained by obtaining the correlation between two images with good symmetry even in a defocused blurred image. That is.

Further, if the amount of image shift on the image plane is quantitatively known, the amount of movement of the focusing lens group in the focused state can be uniquely calculated, the prediction detection becomes possible, and even in the large blur state. There is an advantage that the directions of all the pins and the rear pins can be surely detected and the focusing position can be focused at high speed.

[0034]

In the image shift type focus detecting device, as described above, the longer the focal length of the separator lens forming the secondary optical system, the higher the focus detecting accuracy. However, the amount of prediction is small, and if an attempt is made to secure a desired amount of prediction, the light flux for focus detection is vignetting in the magnification varying portion, and the shading in each sensor array becomes asymmetric.

FIG. 6 is an explanatory view schematically showing the asymmetry of shading. In the figure, in particular, since the light flux near the inside of each sensor array 34 (the side close to the optical axis of the photographing lens) is vignetted by the lens outer diameter of the variable power unit 21a, the image correlation between the two is taken to perform prediction. In some cases it will give erroneous results.

When the focus detecting device having such a structure is adopted as a photographing lens for a video camera, for example, a still image is not required to have high-speed responsiveness, but if the focus is detected in the wrong direction when the defocus amount is largely blurred, the result is not correct. There was a problem in that it exhibited very unsightly behavior in the process of reaching a focus.

A first object of the present invention is to properly set the constitution of two separator lenses which constitute a secondary optical system and a deflecting means which is arranged in the optical path of a taking lens and which guides a light beam to a focus detecting means. Therefore, the present invention provides a focus detection device that prevents shading and improves the prediction accuracy and focus detection accuracy.

On the other hand, there are various methods of initially setting the position of the focus lens group so that the single evaluation scale obtained from the pair of sensor arrays is minimized with respect to the preset window shift amount. The simplest of these methods is to set the taking lens so that the wide-angle end and the telephoto end are in focus when using the image pickup lens with the photoconductor attached, and then shift any window in that state. It is a method of measuring whether the single evaluation scale becomes the minimum value in the case of quantity, and writing the value in a readable / writable non-volatile memory, etc., including variations in manufacturing error.

If such a memory means cannot be prepared separately, the following problems occur.

Generally, the sensitivity of the position of the focusing lens unit is high at the telephoto end but low at the wide-angle end, and the ratio thereof has a difference of about the square of the variable power ratio. Therefore, when adjusting the focus detection device for an object point at infinity, it is possible to move the focusing lens group at the telephoto end so that the single evaluation scale becomes the minimum with a predetermined window shift amount.

However, whether or not the focus determination can be made with the same shift amount even when zooming to the wide-angle end is not necessarily guaranteed by including manufacturing variations. Normally, the position of the imaging lens is adjusted using the difference in the sensitivity of the focusing lens group so as to focus on a fixed position during zooming (hereinafter referred to as “balance adjustment”), and the position is adjusted to a predetermined absolute position. For example, the position sensitivity is the same in the entire zoom range, for example, the master lens group is adjusted in position to match the focus position (hereinafter referred to as tracking adjustment).

Therefore, also for the focus detection device, in order to minimize the single evaluation scale with the same window shift amount in the entire zoom range, the focusing lens unit is position-adjusted and at the same time the zooming unit (variator lens unit and The relative positions of the lens groups after the compensator lens group) must be displaced.

Normally, since the afocal lens group is fixed, the position of the separator lens and the sensor array is integrally adjusted with respect to the dividing means, or the relative position between the separator lens and the sensor array is adjusted. is there.

In the former case, since the light beams emitted from the afocal lens group are substantially parallel to each other, even if the separator lens and the sensor array are integrally moved within this parallel light beam, the positions of two images (two object images) Relationships hardly change.
On the contrary, when the relative position of the separator lens and the sensor array is changed, there is a problem that the image is too sensitive because a large image separation is performed with a slight position adjustment.

The second object of the present invention is to arrange a zoom lens as shown in FIG. 4 in the optical path between the afocal lens group and the diaphragm, and to provide a deflection means for separating and deflecting the light beam to the focus detection means. By properly setting the afocal lens group, the focus position during zooming can be set only by mechanical adjustment, including variations in the manufacture of each element,
Another object of the present invention is to provide a focus detection device which does not need to write each in-focus position in a non-illuminating memory, can have a small circuit configuration, and can perform highly accurate focus detection.

In the case of a video lens or the like, the brightness of the subject is photoelectrically converted on the image pickup surface 30 and the opening / closing of the diaphragm 26 is controlled in accordance with the luminance signal level thereof. If a deflecting means composed of a prism having a half-mirror surface for separate deflection is arranged, a focus detecting light beam (AF light beam) cannot be obtained. For this reason, in many cases, the deflecting means is arranged on the object side of the diaphragm.

However, since the deflecting means composed of the prism is usually constructed by polishing and cutting glass blocks and then laminating the glass blocks, there is a problem that the weight becomes heavy and large.

A third object of the present invention is to appropriately arrange the configuration and arrangement of the deflecting means, which is arranged in the optical path between the variable power portion and the diaphragm, and which guides the light beam to the focus detecting means, and the aperture shape of the diaphragm. An object of the present invention is to provide a focus detection device that can obtain good focus detection accuracy with a simple configuration by setting.

Further, in the image shift method of the TTL method, two images (or a plurality of images having a good symmetry) are separated from each other by using the light flux that has passed through different regions on the pupil plane from the photographing light flux. Normally, as in the conventional example shown in FIG. 4, a deflecting unit is arranged behind the variable power unit and in front of the diaphragm to guide the light beam to the focus detecting unit.

This is because, for example, in a photographing lens for video, the diaphragm always opens and closes in accordance with the brightness, so that a sufficient F number luminous flux cannot be obtained in terms of focus detection accuracy, and therefore the deflecting means is arranged in front of the diaphragm. The light flux is separated and deflected to the focus detection means.

However, in a so-called rear focus type zoom lens in which the focusing lens unit is closer to the image side than the variable power portion, in order to move the whole relay unit or a part of the relay unit at the time of focusing, immediately before the aperture stop. However, there is a problem that the current out-of-focus information is not fed back to the focusing lens group for the reason of extracting the light flux for focus detection.

In some recent rear focus type zoom lenses, some lens groups in the relay group have the functions of both the focusing lens group and the compensator lens group. In such a case, if the light beam for focus detection is taken out immediately before the diaphragm, out-of-focus information is further lost to the focus detection optical system side due to zooming.

In this case, the focus detecting device can detect the shift amount and calculate the position of the focusing lens group and the compensator lens group based on the zooming information of the variator (magnifying lens group). Since there is an open loop control, there is a problem that individual required accuracy becomes strict.

A fourth object of the present invention is to provide, when a rear focus type zoom lens is used as a photographing lens, a deflection means for separating and deflecting a light beam to a focus detection means and a lens group having an appropriate refractive power in a focus detection optical path. Another object of the present invention is to provide a focus detection device having high focus detection accuracy by arranging it and interlocking with a focus lens group.

[0055]

A focus detection apparatus for achieving the first object of the present invention uses a light beam which has passed through a plurality of different areas of a pupil of a photographing lens and which uses an optical means to detect a plurality of images of an object. Form the light intensity distribution of
When the relative positional relationship of the plurality of light amount distributions is obtained by the light receiving means and the focusing state of the photographing lens is detected using the signal from the light receiving means, the optical means has a weak refractive power at the central portion. It is characterized by having a plurality of dull-heart lenses having strong refractive power in the peripheral portion.

In particular, the optical means is characterized in that a plurality of light quantity distributions relating to the subject image are formed by using the light flux that has passed through the deflecting means provided in the optical path of the taking lens.

A focus detecting apparatus for achieving the second object of the present invention is a focus lens group which is fixed during zooming in order from the object side, a zooming lens group, and an image plane variation due to zooming which is corrected. A correction lens group, an afocal lens group for making the output light flux fixed during zooming into substantially parallel light, a deflection means for deflecting the light flux to the focus detection means, a diaphragm, and a fixed lens group fixed during zooming, It is characterized in that an adjusting means capable of adjusting the movement of the afocal lens group on the optical axis is provided.

In particular, the focus detecting means forms a plurality of light quantity distributions for a subject image using light fluxes that have passed through a plurality of different areas of the pupil of the photographing lens, and obtains a relative positional relationship of the plurality of light quantity distributions. The in-focus state of the taking lens is detected.

The focus detecting device for achieving the third object of the present invention guides the light beam deflected by the deflecting means arranged between the variable power lens group and the diaphragm to the focus detecting means to detect the focus. The means forms a plurality of light amount distributions with respect to a subject image using light fluxes that have passed through a plurality of regions of different pupils of the taking lens, obtains a relative positional relationship between the plurality of light amount distributions, and focuses the taking lens. The state is detected, the deflection means is composed of a horizontally long mirror that separates and forms the plurality of light amount distributions, and the deflection point of the light flux of the mirror is arranged eccentrically from the optical axis of the photographing lens. The aperture is characterized by having a flat opening shape that is long in the base line length direction when the aperture is narrowed down.

A focus detecting device for achieving the fourth object of the present invention comprises a variable power lens group, a deflecting means for separately deflecting a light beam to a focus detecting means, a diaphragm, and a focus lens group in order from the object side. A lens group having substantially the same refractive power as the focus lens group and performing the same movement is provided in the optical path of the focus detecting means.

[0061]

1 is a schematic view of a main part of an optical system according to a first embodiment of the present invention, and FIG. 2 is a cross-sectional view of a main part of a separator lens constituting the secondary optical system of FIG.

The figure shows a case where the present invention is applied to a zoom lens for a video camera or a still video camera, and the constitution of a separator lens constituting a secondary optical system as compared with the conventional focus detection device of FIG. Are different, and other configurations are substantially the same.

Next, the structure of FIG. 1 will be described one by one, although it partially overlaps with the conventional focus detection device of FIG.

In the figure, reference numeral 21 denotes a photographing lens (objective lens), which is composed of a zoom lens. Reference numeral 22 is a focus lens group, 23 is a variable power lens group for zooming (variator lens group), 24 is a correction lens group (compensator lens group) for correcting the image plane variation due to zooming, and 25 is an afocal lens. It is a group, and the emitted light flux is substantially parallel light. 26 is an aperture, 27 is a fixed lens group (relay lens group) that is fixed during zooming, 28 is a low-pass filter, 29
Is an image pickup device such as CCD, and 30 is an image plane.

In the figure, the afocal lens group 25
Between the lens and the diaphragm 26, there is disposed a deflecting means 32 which is a half mirror inclined by about 45 degrees with respect to the optical axis for separating and deflecting the light beam by the focus detecting means. The secondary optical system 33 including the two separator lenses (secondary lenses) 33a and 33b through the infrared light cut filter 35 uses the light fluxes from different regions on the pupil plane of the taking lens 21 to obtain two objects. An image is formed on the surface of the light receiving means 34 which is composed of two sensor arrays (light receiving element rows) 34a and 34b.

Reference numeral 37 is a visual field mask, which is disposed either before or after the separator lenses 33a and 33b.
When capturing one subject image, the two subject images are separated.

In the present embodiment, the deflecting means 32, the infrared light cut filter 35, the field mask 37, the separator lens 33, etc. constitute one element of the optical means 31.

Separator lens 33 in this embodiment
(33a, 33b) is the central portion 33a as shown in FIG.
₁ and (33b ₁ ) have a weak refracting power, and the peripheral portion 33a ₂ ,
The refractive power of (33b ₂ ) is formed by a so-called dull-heart lens having a strong refractive power distribution.

In this embodiment, a light quantity distribution relating to two identical subject images is formed on the light receiving element array planes 34a and 34b by using the light flux that has passed through two areas of the pupil of the objective lens by the secondary optical system. is doing. At this time, the relative positional relationship between the two light amount distributions formed on the light receiving element array surface, that is, the amount of deviation of the light amount distributions differs depending on the focus state of the focus lens group 22. For example, the light receiving element array 34
Focus lens group 2 in the arrangement direction of the elements on a and 34b.
2 appears as a lateral shift amount according to the amount of defocus from the planned image plane.

The detection of the in-focus state of the focus lens group 22, that is, the detection of the defocus amount, the relative positional relationship between the two light amount distributions at this time, that is, the lateral deviation amount of the light amount distribution is detected by the light receiving means 34 and calculated. It is done by processing.

In this embodiment, the lens shapes of the deflecting means 32 and the secondary optical system 33 are set as described above. As a result, in the vicinity of the in-focus state, the window for performing the correlation is in the substantially central portion of the sensor array, and since the image has a high degree of sharpness, it is easy to obtain a strong correlation.

Further, the optical image based on the light flux of the central portion on the sensor array used at the time of focusing in order to improve the focus detection accuracy is separated by the separator in order to increase the sensitivity of the deviation of the optical image to the defocus amount of the focusing lens group. The center of the long focal length of the lens is used.

On the other hand, the image for prediction which is formed around the sensor array at the time of defocusing is determined with coarse detection accuracy by using the image forming light from the peripheral portion of the separator lens having a relatively short focal length. ing. In particular, in the case of a video lens or the like, the focusing lens group is moved more slowly than the still image camera, and therefore the prediction precision does not need to be extremely high.

Since the image for prediction is originally a blurred image, even if the refractive power of the peripheral portion is different from the refractive power of the central portion, there is no practical problem as long as the image correlation can be obtained.

As described above, in this embodiment, since the sensitivity of the movement of the image at the time of prediction is low, the sensor length can be shortened, and the focus detector can be downsized, and the downsizing of the entire apparatus can be facilitated. I have to.

Next, the features of the configuration of the second embodiment of the present invention will be described using the configuration of FIG.

The second embodiment is different from the first embodiment in that the afocal lens group 25 can be adjusted on the optical axis and the assembling error of each element of the optical means after the deflecting means 32 is adjusted.

That is, the luminous flux emitted from the afocal lens group 25 is substantially parallel light and is separated by the separator lenses 33a and 33b.
Incident on. Accordingly, the positional relationship between the separator lenses 33a and 33b and the sensor arrays 34a and 34b is set so that the separator lenses 33a and 33b have a desired window shift amount when the object point is at infinity.

Further, the setting is such that the separator lenses 33a, 3a are set in the state of being incorporated in the zoom lens system as shown in FIG.
Positional adjustment between 3b and the sensor arrays 34a, 34b is physically difficult due to space, and is fixed thereafter.
It is said to be immutable.

Next, the optical means 31 and the light receiving means 34 incorporated in the zoom lens system are adjusted as follows so as to obtain a desired window shift amount with respect to the object point at infinity through the variable power portion.

First, the focus lens group 22 is moved with the variable power unit at the telephoto end, the output from the sensor array is read, and the position is fixed so that the in-focus state is achieved.

Next, zooming is performed to the wide-angle end, and the afocal lens group 25 is moved along the optical axis and fixed in position so that the output from the sensor array at that time provides a desired window shift amount. This is because the focus sensitivity of the focus lens group is high at the telephoto end with respect to an object point at infinity, but it is low at the wide angle end, and therefore the afocal lens group 25 is moved to change the focus position. At this time, the afocal lens group 25 is finely adjusted in the optical axis direction by using an adjusting unit composed of a screw or the like formed on the fixed lens barrel 11 and the afocal lens group lens barrel 12.

Further, the state is returned to the telephoto end, the focus lens group 22 is moved for fine adjustment, and the repetition due to the repetition is performed to correct the shift due to zooming.

As described above, according to the present embodiment, the focus position can be set during zooming only by mechanical adjustment including the manufacturing variation of each element, and each focus position is written in the non-shining memory. It has the feature that it is unnecessary and the circuit scale can be small.

Further, after this adjustment, the light flux emitted from the afocal lens group always has the same exit angle regardless of zooming, so that the tracking adjustment by the relay lens group 27, which is the same as the conventional one, according to the position of the CCD 29 is performed thereafter. It also has the feature that

Next, features of the configuration of the third embodiment of the present invention will be described based on the configuration of FIG.

In this embodiment, the deflecting means 32 is composed of a horizontally long total reflection mirror which separates and forms a plurality of light quantity distributions, and the reflection branch point of this total reflection mirror is decentered from the optical axis of the photographing lens. , Are arranged in the lower part of the figure. Further, when the diaphragm 26 is narrowed down, it has a flat opening shape that is long in the direction of the base line, and these points are different from the first embodiment.

That is, the so-called base line length direction in which two images are separated by the separator lenses 33a and 33b is the image pickup element surface 3
It corresponds to the long side (horizontal) direction of 0. Therefore, the total reflection mirror 32 which is the deflecting means is a horizontally long mirror. Further, the optical axis branch point of the focus detection optical path by the total reflection mirror 32 is not on the optical axis of the taking lens but is set slightly decentered in the vertical direction.

Of course, although there is a part in the optical path, there is a shield that blocks the light beam, so the effective aperture ratio decreases, which is eccentric even if the total reflection mirror is on the optical axis. Is also the same. As for the off-axis oblique light flux, since the total reflection mirror 32 does not block the effective total light flux, vignetting does not occur completely although the light quantity has a fixed value.

However, since the principal ray intersects the optical axis in the vicinity of the ordinary diaphragm 26, in the state of a small diaphragm where the luminous flux width is narrowed, if the total reflection mirror 32 is arranged on the optical axis, the total luminous flux is blocked. Therefore, the total reflection mirror 32 is deviated from the optical axis in the vertical direction. At the same time, the diaphragm 26 has a flat opening shape that is long in the horizontal direction when the diaphragm is small.

That is, the horizontally long total reflection mirror 32 is decentered from the optical axis in the vertical direction to form a light beam that is wide in the horizontal direction and thin in the vertical direction so that the light amount loss is reduced. As is conventionally known, such a flat aperture stop is obtained by, for example, forming two stop blades and setting the blade opening direction to the vertical direction.

As described above, according to this embodiment, the light flux from the taking lens can be easily guided to the focus detecting means,
Also, the resolution decreases due to the diffraction effect due to the narrowing of the vertical aperture shape at the time of a small aperture, but since it is the vertical resolution direction that is originally determined by the number of scanning lines, there is little actual damage and good optical performance can be maintained. There is a feature that you can do it.

FIG. 3 is a schematic view of the essential parts of an optical system according to Example 4 of the present invention.

In this embodiment, a so-called rear focus type zoom lens is used as a photographing lens. In the figure, the same elements as those shown in FIG. 1 are designated by the same reference numerals.

In the figure, 51 is a lens group having a positive refractive power which is fixed during zooming and focusing, 52 is a zooming lens group (variator lens group), 53 is an aperture stop, and 54 is a fixed positive lens during zooming. Is a front group of relays having a refracting power, and 55 is a rear group of relays having a positive refracting power for correcting an image plane variation due to focusing and zooming.

Reference numeral 59 is a first mirror which is an element of a deflecting means for branching a part of the light flux for focus detection from the photographing light flux, and 60 is for emitting the divergent light flux from the variator lens group 52 substantially in parallel. Of the afocal lens group 61, a second mirror 61 for making the optical path for focus detection substantially parallel to the optical axis of the photographing system, and 62 has substantially the same refractive power as the focusing lens group 55 of the photographing lens and the same. Group of lenses for moving the lens, 33a and 33b are separator lenses, and 34a and 34b.
b is a sensor array for focus detection, 35 is a near infrared cut filter, and 36 is an aperture mask.

The afocal lens group 60 provided in the focus detection optical path may be provided either before or after the second mirror 61 in the optical path, but the divergent light flux does not spread near the first mirror 59 because the divergent light flux does not spread. It is desirable to place it in front because it will be closed.

In this embodiment, the first mirror 59 is composed of a 45 ° total reflection mirror which is arranged slightly decentered from the optical axis of the taking lens. Sensor array 34 for focus detection
a and 34b may be arranged on the primary image forming surface, or the separator lenses 33a and 33b may be arranged on the secondary image forming surface as re-imaging lenses. Further, a sensor array 34a for focus detection,
34b itself may be provided outside the effective image pickup area on the CCD 29 surface. The near-infrared cut filter 35 is for correcting the spectral sensitivity of the sensor array, but may not be sufficient if the focusing accuracy is satisfied.

In this embodiment, since the movable lens group 62 provided in the focus detection optical path has substantially the same refractive power arrangement as the focusing lens group 55 of the photographing lens, it is integrated with the focusing lens group 55. By doing so, zooming information can be obtained without an electrical correction or a mechanical connection mechanism.

That is, as is conventionally done, the position of the compensator lens group 55 can be determined by detecting the position of the variator lens group 52, and the cam locus can be followed. Therefore, the moving lens group 62 integrated with the compensator lens group 55 does not cause defocus for one specific subject distance.

However, for other subject distances, the focusing operation must be performed based on the shift amount obtained from the focus detection means. However, conventionally, it is not necessary to slightly oscillate the focusing lens group 55 on the optical axis to detect the direction by the focus detection using the image pickup signal, and the feedback operation is performed by approaching the in-focus position based on the obtained shift information. Repeat several times to focus.

As described above, in this embodiment, the mechanism for driving the microscopic vibration of the focusing lens group 55 is omitted, and a focus detecting device having a simple structure utilizing the advantage of the deviation detecting method is obtained.

[0103]

According to the present invention, a focus detection apparatus suitable for a video camera, a 35 mm film camera or the like having a good focus detection accuracy by utilizing the image shift method by setting each element as described above is provided. Can be achieved.

[Brief description of drawings]

FIG. 1 is a first, second, and third embodiments of a focus detection device according to the present invention.
Schematic of the main part of the optical system related to

FIG. 2 is a schematic cross-sectional view of a main part of the secondary optical system in FIG.

FIG. 3 is a schematic view of a main part of an optical system according to a fourth embodiment of the present invention.

FIG. 4 is a schematic view of a main part of a conventional focus detection device.

5 is an explanatory diagram of signal values obtained from the light receiving means of FIG.

6 is an explanatory view showing the relationship between shading by the taking lens of FIG. 4 and a light receiving means.

[Explanation of symbols]

 21 shooting lens 22 focus lens group 23 variable magnification lens group 24 correction lens group 25 afocal lens group 26 diaphragm 27 relay lens group 28 low-pass filter 29 image sensor 31 optical means 32 deflecting means 33 secondary optical system 34 light receiving means 35 infrared Cut filter 51 Fixed lens group 52 Variable magnification lens group 53 Aperture 54 Relay front group 55 Relay rear group

Claims (6)

[Claims] 1. A plurality of light quantity distributions relating to a subject image are formed on a light receiving means surface by an optical means by using light fluxes passing through a plurality of different areas of a pupil of a photographing lens, and the plurality of light quantity distributions are formed by the light receiving means. When the in-focus state of the photographing lens is detected using the signal from the light receiving means, the optical means has a weak refractive power at the central portion and a strong refractive power at the peripheral portion. A focus detection device having a dull-heart lens. 2. The focus detection according to claim 1, wherein the optical unit forms a plurality of light amount distributions regarding a subject image by using a light beam that has passed through a deflecting unit provided in an optical path of the photographing lens. apparatus. 3. A focus lens group which is fixed during zooming, a zoom lens group, a correction lens group which corrects an image plane variation due to zooming, and an exiting light beam which is fixed during zooming are substantially collimated in order from the object side. And an afocal lens group, a deflection means for deflecting the light beam to the focus detection means, a diaphragm, and a fixed lens group that is fixed during zooming, and the afocal lens group can be moved and adjusted on the optical axis. A focus detection device characterized in that adjustment means is provided. 4. The focus detecting means forms a plurality of light amount distributions for a subject image using light fluxes that have passed through a plurality of regions of the photographing lens having different pupils, and shows a relative positional relationship between the plurality of light amount distributions. 4. The focus detection device according to claim 3, wherein the focus state of the photographing lens is detected and detected. 5. A light beam deflected by a deflecting unit arranged between a variable power lens group and a diaphragm is guided to a focus detecting unit, and the focus detecting unit passes through a plurality of regions having different pupils of a photographing lens. The light flux is used to form a plurality of light amount distributions with respect to the subject image, the relative positional relationship between the plurality of light amount distributions is obtained, and the focusing state of the photographing lens is detected. It is composed of a laterally long mirror that separates and forms the distribution, and the deflection point of the light flux of the mirror is arranged eccentrically from the optical axis of the taking lens, and the diaphragm is long in the baseline length direction when narrowing down. A focus detection device having a flat aperture shape. 6. A zoom lens group, a deflecting means for separating and deflecting a light beam to a focus detecting means, an aperture stop, and a focus lens group are arranged in this order from the object side, and the focus lens group and the focus lens group are provided in an optical path of the focus detecting means. A focus detection device comprising a lens group having the same refractive power and performing the same movement.