JPH06303489A - Image pickup device with focal detecting means - Google Patents

Abstract

PURPOSE:To miniaturize a device, and to improve focusing precision by controlling properly the movement of a focusing use lens group at the time of executing focusing operation by using an image signal based on a video obtained by an image pickup system. CONSTITUTION:In the case that zoom operation is being operated, the position detection of a fourth lens group L4 as the focusing use lens group is executed by a second position detecting means, and focal information detection based on output from a focal detection circuit 36 is executed, and each detected result and the information of an infinitesimal vibration impossible area set beforehand in storage data 35 are referred to. As for an area in which infinitesimal vibration is possible, the infinitesimal, vibration of the fourth group L4 is started or continued. Further, the movement data of the fourth leans group L4 along with power variation is read in respectively from the storage data 35. Then, in the case that there is a blur, the moving direction of the fourth group L4 to reduce the blur is discriminated, and in the case of the area in which the infinitesimal vibration is impossible, the infinitesimal vibration of the fourth group L4 is stopped, and further, after lowering zoom speed until the infinitesimal vibration of the fourth group L4 becomes possible, the infinitesimal vibration is restarted, and the driving direction of the fourth group L4 to reduce the blur is discriminated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image pickup apparatus having focus detecting means, and more particularly, to a focusing operation of an image pickup system by using an image signal obtained from an image formed on the surface of the image pickup means by the image pickup system. It is suitable for a video camera, an electronic still camera, a 35 mm film camera, and the like that have detected focus.

[0002]

2. Description of the Related Art Conventionally, various image pickup apparatuses have been proposed in which a focus detection means for detecting the focus of a photographing system is provided in a part of a camera body.

Various methods such as an active type and a passive type have been proposed as a focus detecting method for the photographing system. Of these, the focusing lens group that performs the focusing action on the optical path length between the subject and the image pickup surface is slightly vibrated on the optical axis, and the image signal that changes at this time is used to move the focusing lens group on the optical axis. A focus detection device that detects the focus direction of the imaging system by discriminating the moving direction is proposed in, for example, JP-A-63-193775.

According to the publication, the focusing means having a focusing action also serves as a mechanism for slightly changing the optical path length for determining the moving direction of the focusing means.

With this, a special optical path length fine movement mechanism is not required, and a focus detecting device having a simple structure and low cost is constituted.

[0006]

A so-called rear focus type zoom having, as an image pickup system, a zoom lens group and a focus lens group that corrects an image plane variation due to zooming and performs a focusing action. The lens is currently used in many cameras because the whole lens system is small and quick focusing operation is possible.

When such a rear focus type zoom lens is applied to the focus detecting device proposed in the above-mentioned Japanese Patent Laid-Open No. 63-193775, when a small vibration of the focusing lens group is performed, The focusing lens group needs to be moved in the optical axis direction during zooming for the same subject (same object distance) to hold the image surface at a fixed position.

At this time, it is necessary for the focusing lens group to simultaneously perform both movement for correction of image plane variation and microvibration for focus detection.

In this case, depending on the photographing system, the focusing lens group must be moved at high speed in order to keep the image plane variation due to zooming, and as a result, it becomes very difficult to perform minute vibrations. Problems arise.

In such a case, for example, in order to move the focusing lens group at high speed and at the same time to perform minute vibrations, the motor as the driving means for moving the focusing lens group becomes large, and the optical system The whole is getting bigger. Further, there is a problem that the focus detection accuracy is also lowered.

According to the present invention, when the focusing lens group is slightly vibrated on the optical axis and the focusing operation is performed using the image signal based on the image obtained from the photographing system at this time, the focusing lens group An object of the present invention is to provide an image pickup apparatus having a focus detection unit capable of performing highly accurate focus detection (focusing operation) while downsizing the entire apparatus by appropriately controlling the movement.

[0012]

An image pickup apparatus having a focus detection device according to the present invention includes a lens group for zooming and a lens group for focusing for correcting an image plane variation due to zooming and focusing. And a focus detection system for performing focus adjustment of the photography system by obtaining an image signal from an image formed on an imaging means surface by the photography system. Direction determining means for determining the moving direction of the focusing lens group by using an image signal obtained from the image pickup means when the focusing lens group is slightly vibrated in the optical axis direction, and the variation during zooming. When at least one of the magnification lens group and the focusing lens group is within a predetermined range on the optical axis, and the image signal obtained by the image pickup means is outside the predetermined range, the focusing lens group is small. After slowing down the zooming speed of the zoom lens group without vibrating, It is characterized by performing the fine vibration of the focusing lens group and a calculating means for determining the direction of movement of the lens group focusing 該合.

[0013]

According to the present invention, when the above-described rear focus type zoom lens is used as the photographing system, it is not possible to simultaneously perform focus holding that fluctuates due to zooming and minute vibration of the focusing lens group that performs the focusing action. In this case, if the above-mentioned minute vibration is stopped, and as a result blurring (a circle of confusion with a predetermined diameter or more) occurs, the zoom speed of the zoom lens group is slowed down and the above-mentioned minute vibration is restarted. The focus direction can be detected with high accuracy by quickly determining the driving direction of the focusing lens group.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a schematic view of a main part of a first embodiment when an image pickup apparatus having a focus detecting means of the present invention is applied to a video camera.

In this embodiment, a rear focus type zoom lens is used as a photographing system.

In the figure, L1 is the first group, and the lenses 19, 2 are
It has 0 and 21. L2 is the second group, and the lens 2
It has 4, 25, 26.

In this embodiment, the first lens unit L1 and the second lens unit L2 are moved on the optical axis to perform zooming. L3 is the third group,
It has lenses 11, 12, and 13. The fourth lens unit L4 includes lenses 4 and 5, and moves on the optical axis to correct an image plane variation due to zooming and perform focusing.

In this embodiment, the third lens unit is fixed during zooming and focusing. Hereinafter, the first group and the second group are also referred to as variable power lens groups, and the fourth group is also referred to as a focusing lens group.

In the present embodiment, the fourth lens unit is slightly vibrated in the optical axis direction, and the moving direction of the fourth lens unit is determined from the image signal obtained by the focus detection unit 36 via the image pickup means 2 at this time. Focusing operation is performed by moving the fourth lens unit on the optical axis.

In FIG. 1, reference numeral 1 denotes a base cylinder, and this base cylinder 1
A support portion (not shown) connected to the camera body via an adapter or the like is provided at the rear portion, and an image pickup member (image pickup means) 2 such as a CCD is attached.

The fourth group lens frame 3 holds the respective lenses 4 and 5 of the fourth group L4, and the output shaft of the step motor 6 and the feed screw 7 are engaged with the belt 8 so that the guide bar 9 is fixed to the guide bar 9. Along the optical axis to correct the image plane variation due to zooming and to perform focusing.

The third group lens frame 10 has an integral structure with the base cylinder 1, and holds the lenses 11, 12, and 13 of the third group L3. The output shaft of the iris motor 14 is the diaphragm rotation frame 1
5 and opens and closes the aperture of the diaphragm 16. The fixed lens barrel 17 is engaged with the first lens outer frame 18 by a helicoid.

Each lens 19, 20, 21 of the first group L1 is held by a first group lens inner frame 23. The first lens outer frame 18, the first group lens inner frame 23, and the cam ring 22 have an integrated structure.

The lenses 22, 23, 24 of the second lens unit L2 are held by the second lens unit frame 27, and the second lens frame 27 is engaged with the cam ring 22. Zoom motor 2
As the lens unit 8 rotates, the first lens unit L1 and the second lens unit L2 respectively move in the optical axis direction, thereby performing zooming.

When the main switch (main SW) 29 is closed, the power-on reset circuit 30 operates to perform initial setting when the power is turned on. Zoom switch (Zoom S
When W) 31 is closed, the zoom direction signal is fetched by the CPU 32, and the zoom motor driver 33 operates to move the zoom motor 28.

In the image pickup system of the present embodiment, the fourth lens unit L4, which serves as a focusing lens unit, also corrects the image plane variation associated with zooming, so that the fourth lens unit in the in-focus state is changed by changing the focal length. The position on the optical axis is different. Therefore, if the fourth lens unit is not moved to a predetermined position during zooming, defocus occurs.

For this reason, in this embodiment, the zoom encoder (first position detecting means) (not shown) detects the position on the optical axis of the first lens unit L1 as a variable power lens unit by the read circuit 34 of the zoom encoder. Output to the CPU 32.
The CPU 32 uses the output, the stored data 35, and the focus detection unit 3
The step motor 6 is driven through the step motor drive pulse output circuit 37 and the step motor driver 38 according to the information from 6.

The step motor drive pulse count circuit 39 counts the number of pulses applied to the step motor driver 38 to detect the position of the fourth lens unit L4 on the optical axis.

The focus detecting section 36 detects the amount of blur by detecting the level of the high frequency component in the video signal from the image pickup member 2.

FIG. 2 is an explanatory view showing the high frequency component level of the video signal with respect to the position on the optical axis of the fourth group for focusing.

In the focused state P ₀ , the level of the high frequency component becomes maximum, and the position P ₀ of the fourth lens unit on the optical axis at this time.
Focusing can be achieved by determining. Further, in the defocus state, a signal having a waveform as shown by 50 and 51 in FIG. 2 is obtained by slightly vibrating the fourth group in the optical axis direction, and the CPU 32 having a direction discriminating means depending on the phase state of the signals 50 and 51. Can determine the driving direction of the fourth group.

However, in the rear focus type zoom lens according to the present invention, since the in-focus state cannot be maintained unless the fourth lens unit is moved at high speed on the optical axis during zooming as described above, minute vibration cannot be performed. There are cases.

FIG. 3 shows the position (movement locus) of the fourth lens unit on the optical axis with respect to the zoom position (focal length) at infinity, 3 m, 1 in the rear focus type zoom lens according to the present invention.
It is explanatory drawing shown for every object distance, such as m.

In this embodiment, as is clear from the curves in FIG. 3, the curves greatly change on the long focus side. That is, it is necessary to move the fourth lens group at high speed on the long focus side.

Therefore, in this case, the aforementioned minute vibration is temporarily not performed. However, in that case, if blurring occurs, it is impossible to determine the driving direction of the fourth lens group described above, and the blurring may expand.

Therefore, in the present invention, the zoom speed is set to be slow when blur occurs when the above-mentioned minute vibration is not performed. Since the moving speed of the fourth lens group during zooming is proportional to the zooming speed, if the zooming speed is slowed down, the above-described minute vibration and focus correction associated with zooming can be performed at the same time.

FIG. 4 shows a flowchart relating to the movement of each lens unit during zooming of this embodiment.

In the present embodiment, the flow is configured to make one round in 1/60 seconds, for example.

First, at step 101, the power source of the video camera main body is turned on, and the initial setting operation is completed. Then, in step 102, it is determined whether or not the zoom operation is performed. If there is no zoom operation, the control shifts to the normal routine of step 103. Step 10 if zoom operation is being performed
In step 4, the position of the first group lens is detected, in step 105, the position of the fourth group lens is detected by the second position detecting means, and then in step 106, focus information detection based on the output from the focus detection circuit 36 is performed.

In step 107, the results of steps 104 and 105 and the above-mentioned information of the micro-vibration impossible area preset in the storage data 35 are referred to.

If it is a region where minute vibration is possible, step 10
8, the minute vibration of the fourth group is started or continued.

In the next step 109, if the blur is at a level that does not cause a problem, the information in step 106 is used in step 11
If it is out of focus, the process proceeds to step 111, and the movement data of the fourth lens group associated with zooming is read from the storage data 35.

If the image is blurred, step 112 is further executed.
At, the moving direction of the fourth group that reduces the blur is determined. On the other hand, if it is determined in step 107 that the microvibration is impossible, the process proceeds to step 113 to stop the microvibration of the fourth group.
Or continue the suspension.

In step 114, as in step 109, blurring is judged, and if blurring, step 115,
If there is no blur, go to step 110.

If the image is out of focus, the steps 116 and 1 are further executed.
After proceeding to 17 and 118, the zoom speed is reduced until the microvibration of the fourth group becomes possible, and then the microvibration is restarted to determine the driving direction of the fourth group in which the blurring is reduced.

Based on the above fourth group driving information, the fourth group is driven in step 119, and one round is completed.

The contents of the stored data 35 constituting the present invention include the position of the focusing lens unit relating to zooming, the speed of the focusing lens unit during zooming, and the position or speed of the focusing lens unit during zooming. It is also possible to include a constant for calculation, a calculation formula or both, a positional relationship between the variable power lens group and the focusing lens group regarding the subject distance, and the like.

[0048]

As described above, according to the present invention, when the focusing lens group is slightly vibrated on the optical axis and the focusing operation is performed by using the image signal based on the image obtained from the photographing system at this time. ,
By appropriately controlling the movement of the focusing lens group,
It is possible to achieve an image pickup apparatus having a focus detection unit capable of highly accurate focus detection (focusing operation) while reducing the size of the entire apparatus.

[Brief description of drawings]

FIG. 1 is a schematic view of a main part of a first embodiment when the present invention is applied to a video camera.

FIG. 2 is an explanatory diagram of a focus detection principle according to the present invention.

FIG. 3 is an explanatory diagram showing the positions on the optical axis of the focusing lens group for each zoom position in the present invention.

FIG. 4 is a flowchart according to the present invention.

[Explanation of symbols]

 L1, L2 zoom lens group L4 focusing lens group 2 imaging means 32 CPU 35 stored data

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location G02B 7/36

Claims (2)

[Claims] 1. A photographic system having at least two lens groups of a variator lens group and a focusing lens group for correcting an image plane variation due to the magnification change and focusing, and an image pickup means by the photographic system. And a focus detection system for performing focus adjustment of the photographing system by obtaining an image signal from an image formed on a surface, the focus detection system being capable of slightly vibrating the focusing lens group in the optical axis direction. Direction determining means for determining a moving direction of the focusing lens group using an image signal obtained from the image pickup means, and at least one of the zooming lens group and the focusing lens group is a light beam during zooming. When the image signal obtained by the image pickup means is outside the predetermined range on the axis and the focusing lens group is not vibrated minutely, the zooming speed of the zooming lens group is slowed down. Then, a minute vibration of the focusing lens group is performed to move the focusing lens group. An image pickup apparatus having a focus detection unit, comprising: a calculation unit that determines a direction. 2. An image pickup having a focus detection unit according to claim 1, wherein the image signal obtained by the image pickup unit is out of a predetermined range when the blur amount of the photographing system is equal to or larger than a predetermined amount. apparatus.