JPH05224118A - Automatic focusing device - Google Patents

Abstract

PURPOSE:To provide an inexpensive phase difference detection type automatic focusing device where a field lens having negative power is arranged behind an image pickup equivalent surface, a pair of separator lenses and a phase difference detecting device are arranged in order behind the field lens and the number of parts of an optical member is reduced to decrease position adjusting elements. CONSTITUTION:A luminous flux divided to detect focus by a split prism 7 is focused by a pair of separator lenses 4 and 4 through a field lens 24 having the negative power to be formed into an image on a pair of line sensors 8 and 8 in a phase difference detecting device 5 positioned behind the lenses 4. Then, a phase difference is calculated by a processing circuit 25 in the device 5 based on deviation between a pair of object images formed on the line sensors 8 and 8, and focusing is executed by moving a focusing lens group 26 in an optical axis direction based on the calculated phase difference.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic focusing device, and more particularly to a phase difference detecting type automatic focusing device incorporated in a zoom lens of an optical device such as a VTR camera.

[0002]

2. Description of the Related Art Conventionally, an automatic focusing device of this type is shown in FIG.
As shown in, the field lens 3, the pair of separator lenses 4 and 4, and the phase difference detection device 5 are sequentially arranged further behind the image pickup equivalent surface 2 located behind the relay lens 1. In the relay lens 1, a light flux for focus detection, which is split by an optical path splitting prism (optical path splitting optical system) 7 among the light fluxes that have passed through the zoom lens (shooting optical system) 6, is provided near the image pickup equivalent surface 2. Can be imaged. Also,
The field lens 3 can magnify the image formed near the image pickup equivalent surface 2 to some extent, and the pair of separator lenses 4 and 4 focus the magnified image to form a pair of phase difference detection devices 5. An image can be formed on the line sensors 8, 8.

The line sensors 8 and 8 are composed of a CCD or the like which receives a pair of subject images formed by the separator lenses 4 and 4 and photoelectrically converts them, and processes them via cables 9 and 9. It is connected to the circuit 10. The processing circuit 10 can determine the in-focus state based on each electric signal generated according to the luminous intensity distribution in each pixel of the line sensors 8 and 8.

The image formation on the line sensors 8 and 8 approaches the optical axis 11 side in the front focus state where the subject image is formed in front of the image pickup equivalent surface 2 (point A in the figure), and reversely. When the image is formed behind the imaging equivalent surface 2 (point B in the figure), the image is moved away in the post-focus state, and when focused on the imaging equivalent surface 2, the image appears at an intermediate position between the front pin and the rear pin. Therefore, the processing circuit 10 calculates the deviation amounts Δa and Δb of the image forming point with respect to the imaging equivalent plane 2 based on the inter-image distance lx of the pair of images formed on the line sensors 8 and 8, and Based on the calculated phase difference, the focus lens 6a of the photographing optical system 6 is moved in the direction of the optical axis 12.

[0005]

However, since the conventional automatic focus adjusting device is provided with the optical members of the relay lens 1, the relay lens 3, and the separator lenses 4 and 4, there are many position adjusting elements for the optical members. However, there is a drawback that it takes a long time to adjust the position. Further, the conventional automatic focus adjusting device has a large number of parts of the optical member, and thus has a drawback of high cost.

The present invention has been made in view of the above circumstances, and an object thereof is to reduce the number of parts of an optical member to reduce the number of position adjusting elements and to provide an inexpensive phase difference detecting type automatic focusing device. And

[0007]

The present invention achieves the above object.
In order to do this, at least the focus lens of the shooting lens
For focus detection by the optical path splitting optical system installed at the rear
Beam of light is separated, and the separated beam for focus detection is focused.
Imaging on each of a pair of sensors via the detection optical system
Then, based on the output of the pair of sensors, each sensor is connected.
Calculate the phase difference of the optical image to be formed,
Based on the above, the focus lens is moved to the in-focus position.
An optical system for focus detection in an automatic focus adjustment device
Is a negative light which diverges the separated light flux for focus detection.
A field lens having power and the field lens
The light flux diverging through the
Composed of a pair of separator lenses for focusing on
It is characterized by

[0008]

According to the present invention, since the light flux diverged by the field lens having negative power is focused on the pair of sensors through the pair of separator lenses, an object is formed on the pair of sensors. An image is formed. Then, a phase difference is calculated based on the inter-image shift amount of the pair of object images formed on the pair of sensors, and the focus lens of the photographing optical system is moved in the optical axis direction based on the calculated phase difference. ..

As described above, according to the present invention, since the field lens having negative power is attached to detect the focus, the conventional automatic focus adjusting device for detecting the focus using the relay lens and the field lens is used. Compared to
The number of parts of the optical member is reduced. As a result, the automatic focus adjustment device of the present invention has fewer position adjustment elements and is less expensive than conventional automatic focus adjustment devices.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of an automatic focusing apparatus according to the present invention will be described in detail below with reference to the accompanying drawings. FIG. 1 shows an embodiment of a zoom lens 6 of a VTR camera equipped with an automatic focus adjusting device 20 according to the present invention, and the same or similar members as those in the conventional example shown in FIG. And explain.

In FIG. 1, an automatic focus adjusting device 20 has a field lens 24 having a negative power, that is, a concave lens, arranged behind an image pickup equivalent surface 22, and a pair of separator lenses 4 arranged behind the field lens 24. 4 and the phase difference detection device 5 are arranged in order. The field lens 24, among the light flux that has passed through the zoom lens 6,
The light flux for focus detection split by the optical path splitting prism 7 can be diverged. Further, the field lens 24 can refract the light flux and form a virtual image in the vicinity of the imaging equivalent surface 22. Further, the pair of separator lenses 4 and 4 focus the virtual image through the field lens 24, and the pair of line sensors 8 of the phase difference detection device 5.
8 can be imaged.

The line sensors 8 and 8 are composed of CCDs or the like for receiving a pair of subject images formed by the separator lenses 4 and 4 and photoelectrically converting the received images. The line sensors 8 and 8 are connected to the processing circuit 25 via cables 9 and 9, respectively. The processing circuit 25 can determine the in-focus state based on each electric signal generated according to the luminous intensity distribution in each pixel of the line sensors 8 and 8.

The image formation on the line sensors 8 and 8 approaches the optical axis 11 in the front focus state where the subject image is formed in front of the image pickup equivalent surface 22 (point P in the figure), and conversely. When the image is formed behind the imaging equivalent surface 22 (point Q in the figure), the image is moved to the optical axis 11 side in the rear focus state, and when focused on the imaging equivalent surface 22, it is located at an intermediate position between the front pin and the rear pin. appear. Therefore, the processing circuit 25 includes the line sensors 8, 8
Based on the inter-image distance Lx of the pair of images formed above, the shift amounts Δp and Δq of the image forming point with respect to the image pickup equivalent surface 22 are calculated, and based on the calculated phase difference, the photographic optical system 6 The focus lens group 26 can be moved in the optical axis direction 12.

Reference numeral 28 is a variator lens group that changes the focal length, and reference numeral 30 is a compensator lens group that corrects the focal shift caused by the movement of the focal length. Further, reference numeral 32 is a compensator lens group 30.
Together with this, it is a master lens group that corrects the focus shift.
Therefore, according to the automatic focus adjusting device 20 configured as described above, the field lens 24 having a negative power is attached to detect the focus. Therefore, the conventional focus detection using the relay lens and the field lens is performed. It is possible to reduce the number of parts of the optical member as compared with the automatic focus adjusting device. As a result, according to the automatic focus adjusting device 20 of the present embodiment, the number of position adjusting elements of the optical member is reduced and the cost is reduced as compared with the conventional automatic focus adjusting device.

[0015]

As described above, according to the automatic focus adjusting apparatus of the present invention, the field lens having negative power is attached to detect the focus. Therefore, the conventional relay lens and field lens are used. The number of parts of the optical member is smaller than that of the automatic focus adjusting device. As a result, the automatic focus adjustment device of the present invention has fewer position adjustment elements for the optical member and is less expensive than the conventional automatic focus adjustment device.

[Brief description of drawings]

FIG. 1 is a front view showing an embodiment of a zoom lens to which an automatic focusing device according to the present invention is applied.

FIG. 2 is a front view showing an embodiment of a zoom lens to which a conventional automatic focusing device is applied.

[Explanation of symbols]

 4 ... Separator lens 5 ... Phase difference detection device 6 ... Zoom lens 7 ... Optical path splitting prism 8 ... Line sensor 10 ... Processing circuit 20 ... Automatic focusing device 22 ... Imaging equivalent surface 24 ... Field lens 25 ... Processing circuit

Claims (1)

[Claims] 1. A light beam for focus detection is separated by an optical path splitting optical system disposed at least behind the focus lens of the taking lens, and the separated light beam for focus detection is passed through the optical system for focus detection. An image is formed on each of the pair of sensors, the phase difference between the optical images formed on each sensor is calculated based on the outputs of the pair of sensors, and the focus lens is focused based on the calculated phase difference. In the automatic focus adjusting device for moving to a position, the optical system for focus detection diverges via the field lens having negative power for diverging the separated light flux for focus detection and the field lens. An automatic focus adjusting device, comprising: a pair of separator lenses for forming an image of a light flux on the pair of sensors, respectively.