JPH0455806A - Lens position controller for zoom lens - Google Patents

Abstract

PURPOSE:To absorb erroneous components of fluctuations by production and to allow the exact control of lens positions by computing the extending length of a focal lens in accordance with the data stored by a memory means in correspondence to the distance information of a distance measuring means and the lens position of a variable power lens. CONSTITUTION:A distance measuring instrument 11 which is a non-TTL (Through The Lens) and active type measures the distance up to a subject in accordance with a triangulation distance measuring system and transmits this subject distance information to a CPU 12. The CPU 12 computes the actual extending length of a focal group, for example, by calculating the number of extending pulses in accordance with the zoom position information from a position detecting means 8, the subject distance information from the distance measuring instrument 11 and respective sets of the data from memory means 13,14. The fluctuations by the production errors with each cameras are absorbed and corrected and the lens positions of the zoom lens are exactly controlled.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a lens position control device for a lens group constituting a zoom lens, and particularly to a lens position control device for a rear focus type zoom lens.

[Prior art]

In recent years, it has become common for still cameras and video cameras to be equipped with autofocus mechanisms that can automatically adjust the focus. At this time, there is a demand for a zoom lens that has high focusing accuracy, high focusing speed, and can even focus on close objects.

In response to these demands, for example, Japanese Patent Application Laid-Open No. 62-2421
As shown in Publication No. 3, Japanese Patent Application Laid-open No. 57-78513, etc., a so-called rear focus type zoom lens performs focusing by moving a lens group on the object side that has a relatively small diameter other than at least the lens group. is preferred.

However, when controlling the position of the focusing lens of such a zoom lens, the amount of extension of the focusing lens is not only related to the object distance, but also to the zoom position, that is, the focal length. The amount of movement for a subject at a distance is larger on the telephoto side than on the wide-angle side.

Therefore, it is difficult to simply apply a conventional mechanism having a unique cam groove to the movement of this lens.

For example, JP-A-49-115322, JP-A-62-296110, JP-A-62
In Japanese Patent No. 284317 and the like, proposals have been made to control the position of the focusing lens of a rear focus type zoom lens. In particular, in Japanese Patent Laid-Open No. 62-284317, information related to the movement trajectory of the focusing lens according to the focal length is stored so that the focusing lens traces an appropriate zoom trajectory even when the focal length changes. We are proposing technology.

[Problem that the invention seeks to solve]

However, in reality, the locus of movement or the amount of extension of the focusing lens will differ for each individual lens due to manufacturing errors in each part, including the lens, and assembly errors during assembly work. A problem arose. Therefore, if the focusing lens is extended according to the set value or the designed value, a shift in focus may occur, and good photographing may not be possible.

Conventionally, as a solution to this problem, a lens group other than the variable magnification lens group whose sensitivity to focus differs depending on the zoom position, that is, the lens group, is moved along the optical axis and the difference in sensitivity is utilized. The above-mentioned deviation in focus position was corrected. Hereinafter, this will be referred to as balance adjustment of the focus position at the wide-angle end and the telephoto end.

After performing the above balance adjustment, the focus positions at the focal lengths at the wide-angle and telephoto ends will exactly match, but due to variations due to manufacturing errors of each lens group that makes up the lens system mentioned above, There have been cases where the focus position at the time of the shooting shifts, a so-called intermediate focus shift.

SUMMARY OF THE INVENTION In view of these problems, it is an object of the present invention to provide a lens position control device for a zoom lens that can absorb errors caused by manufacturing variations and accurately control the lens position.

[Means for solving problems]

The present invention is characterized in that in a lens position control device for a zoom lens that performs focusing by moving a focus lens group located behind a variable magnification lens, a distance measuring means detects the position of the variable magnification lens. a detecting means for detecting, a storage means for storing, for each position of the variable magnification lens, movement data from a reference position to a position of the focus lens group when the zoom lens is focused at a predetermined subject distance; and a distance measuring means. The present invention further comprises a calculation means for calculating the amount of extension of the focus lens based on distance information of the mounting means and data stored in the storage means corresponding to the lens position of the variable power lens.

〔Example〕

The present invention will be described in detail below based on the drawings. Figure 1 shows
1 is a diagram showing the configuration of a lens position control device according to the present invention. 1.2.3 shows the lens groups constituting the zoom lens, in order: a fixed lens group having positive refractive power;
A variable power lens group that has negative refractive power and moves along the optical axis during zooming, and a variable power lens group that has positive refractive power that corrects image plane movement due to zooming, and moves along the optical axis for focusing. Each of the focus lens groups moving along is shown. 4 is aperture, 5 is C
This is the imaging surface of a CD, etc.

6 is a drive means for moving the variable power lens group 2, 7 is a drive means for moving the focus lens group 3, and 8.9 is an encoder for detecting the positions of the variable power lens group 2 and the focus lens group 3, respectively. It is a position detection means.

In particular, the zoom encoder of the position detection means 8 divides the zoom range from the wide-angle end to the telephoto end into 13 parts. Reference numeral 10 denotes an operating member for setting the focal length of the zoom lens, and outputs a setting signal to the driving means 6 through the CPU 12. Further, although not shown, the driving means 6 similarly changes the magnification of the external finder.

11 is non-TTL (Through The Le
ns) is a known active type ranging device,
The distance to the subject is measured based on the triangulation method, and this subject distance information is sent to the CPU.

13 is an electrically erasable non-volatile memory (E2PROM)
:Electrical Erasable a
nd Programmable Re a d On
It is a storage means for I y M e m o r y ). Reference numeral 14 denotes a fixed storage means (ROM) that stores the shift amount of the focus lens according to the object distance. still,
The contents stored in the E2PROM 13 and ROM 14 will be described later.

12 is a CPU (Central process)
r unit), the zoom position information from the position detection means 8, the subject distance information from the distance measuring device, and the storage means 13
．． The actual amount of movement of the focus lens group, for example, the number of movement pulses, is calculated based on each data from 14. 14 is a release button, switch Sw is turned on at the first stroke, and switch 5 is turned on at the second stroke.
A known switch having w2 sends a distance measurement start signal to the CPU in the first stroke, and sends out a photographing start signal in the second stroke.

Next, the contents written in each of the above-mentioned ROMs will be explained. The amount of extension of the focus lens group is determined by the optical characteristics of the designed zoom lens, and this value is basically calculated based on the design value.
In reality, as described above, out-of-focus occurs due to manufacturing errors of each component including the lens, and further assembly errors.

Therefore, in this embodiment, as shown in FIG. 1(B), at the time of manufacturing, first, a specific reference object distance is determined for each of the 13 zoom positions, for example, using a focus position detection measurement tool (not shown) for an object at infinity. Reference position l when the focus lens group 3 is moved and focused. Data regarding the amount of feed from the machine is written to E2FROM. Note that the specifications of the zoom lens of this embodiment are determined so that a convex locus is drawn toward the object side when zooming from the wide-angle end to the telephoto end. And 11 is the extension position of the focus lens 3 when focusing on an object at infinity! ! 2 indicates the extended position of the focus lens 3 when focusing on the closest object.

Further, W indicates the wide end, and T indicates the tele end. Reference numeral 9a indicates an encoder, which corresponds to the position detection means 9 in FIG. 1(A).

In this way, each zoom position is determined, and E”FROM
Data for each movement of the focus lens written in D a (Z i , oo ) (i=
l~l3). In this embodiment, the focus lens extension data is obtained and written in correspondence with all zoom positions, but if the zoom area exceeds a real number, several zoom positions may be sampled. Alternatively, other points may be determined by interpolation.

On the other hand, the fixed storage means 14 also stores the shift amount of the focus lens group based on the object distance information of the distance measuring device 11 from the focus lens group position j71 when focusing on an object at infinity for each zoom position. There is.

Although the shift amount of the focus lens group written in the ROM 14 is a function of information on the zoom position and subject distance, this shift amount is set to 5hift (ZiSo
bj).

According to the contents of each of the above storage means, the CPU 12 uses the information of the zoom position (Zi) from the position detection means 8 to
First, while reading out the amount of extension Data (Zi, 00) of the focus lens group from the reference position lo from the E2PROM 13, the RO is also read out based on the zoom position information (Zl) and object distance information (Obj) from the range finder 11.
Read the shift amount 5hift (Zi, obj) from M14. Then, the CPU 12 calculates Data (Zi, oo) +5hift (Zi
, obj) to calculate the actual amount of extension of the third lens group as the number of pulses.

Then, when SW2 of the release button 14 is pressed,
First, the driving means moves the focus lens 3, but when the number of pulses generated by the encoder that detects this movement matches the number of feeding pulses determined by calculation, the driving means 7
The operation of the lens is stopped to perform accurate lens position control.

Although the zoom lens of the present embodiment described above is a rear focus zoom lens having a three-group configuration, the present invention is not limited to this zoom lens type. It consists of a lens group, a second lens group with negative refractive power, a third lens group with positive refractive power, and a fourth lens group with positive refractive power, and the second lens group and the fourth lens group are moved. It can also be applied to lens types that perform zooming.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to absorb and correct variations due to manufacturing errors between cameras, and accurate lens position control of the zoom lens can be performed.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of the present invention, especially FIG. 1(B).
FIG. 2 is a diagram for explaining the movement control operation of the focus lens group.

Claims (1)

[Claims] (1) In a lens position control device for a zoom lens that performs focusing by moving a focus lens group located behind a variable magnification lens, a distance measuring means, a detection means for detecting the position of the variable magnification lens, and a predetermined position from a reference position are provided. storage means for storing, for each position of the variable magnification lens, data on the movement of the zoom lens to the position of the focus lens group when the zoom lens is in focus for a subject distance of A lens position control device for a zoom lens, comprising a calculation means for calculating an amount of extension of the focus lens based on data stored in the storage means corresponding to a lens position of a magnification lens.