JPS5940616A - Focusing method of zoom lens - Google Patents

Abstract

PURPOSE:To reduce the size of a zoom lens, by arranging a lens group which has small refracting power and moves associatively with magnification varying operation behind a variable power part, and performing focusing by the movement of part of the lens group. CONSTITUTION:The focusing lens group F having the small refracting power is arranged behind the variable power part consisting of a lens group V for magnification variation and a lens group C for compensation. When the variable power part performs zooming operation from a wide-angle end to a telephoto end, the lens group F is moved in an object-side direction. Then, a lens group having negative refracting power on the image plane side of the lens group F is moved from an infinite distance object to the clsest object in the image-plane direction to perform focusing operation. Consequently, the difference in the extension amount of the lens group for focusing is reduced. Further, the need to increase the overall length of the lens system is eliminated and the size of the zoom lens system is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a focusing method VC for a zoom lens, and in particular, focusing is performed by a lens group -SB of a lens group IM located closer to the image plane than a variable power section of an optical system. This relates to the so-called super γ-focus method VC.

Most conventional zoom lens focusing methods involve a lens group located closer to the object side than the lens group normally involved in zooming. In this case, regardless of the focal length of the entire optical system, the extension of the focusing lens group corresponding to the object distance is uniquely determined to be 0. In other words, once focusing is performed, the focus will change even if zooming is performed thereafter. does not occur. Also, in the case of a lens system that is composed of about two lens groups or three lens groups, which is known as a short zoom, and focuses on the object with a lens group that has a negative refractive power, Once you have focused, the change in focus will be negligible even if you zoom afterwards.
@iJ I'm thinking of a way to turn the ball off.

In the case of the front lens focusing method, the claw needle of the lens group that moves with focus is generally large, and the outer diameter of the s-4fc lens is also large, so when used with an automatic focusing device d that automatically focuses using a motor etc. However, it has the disadvantage that it requires a large amount of electrical power and takes a long time to focus. On the other hand, as an optical system for a camera using the automatic focusing device M, focusing can be performed using a lens group that is close to the image plane and has a small outer diameter, rather than using the cocoon focus method. The so-called IJ-1'-focus method, the method of focus is 1,
In this case, the extension cover of the focusing lens group for a certain object distance ibi# differs greatly depending on the focal length 41. That is, there is a drawback that even once the focus is set, the focus position changes unless tz zooming is performed.

The present invention is arranged eζ 1'' close to the focusing lens m + optical system surface 1illll, and is lightweight and has a small lens outer diameter.Especially when used in a camera equipped with an automatic focusing device, the lens The load on the drive system for moving the group (il) can be reduced, and in the history of The objective of the present invention is to provide a focusing method for a zoom lens that can reduce the size of the lens and reduce the time required for focusing. The variable magnification lens group V has at least one lens group that moves on the optical axis in order to change the distance, and the image plane position If that fluctuates due to the movement of the variable magnification lens group V is set to a constant value (
In order to maintain the lens at the optical axis, the lens # that moves on the optical axis is linked with the variable power function of the variable power section consisting of a lens group O for correction and one lens group O for correction, and the variable power section located behind the variable @. A lens group F having a small composite refractive power consisting of a plurality of lens groups that move symmetrically is arranged, and some of the lens groups in the lens group F are moved to achieve focus.

A lens group p having a small refractive power is disposed behind the variable power unit composed of a plurality of lens groups VC1.

By moving this lens #F on the original axis in conjunction with the zooming action, the imaging magnification of each lens group constituting the lens group F can be changed. For this reason, the focusing method for some of the lens groups in the lens combination 1 can reduce the difference in line width between the lens groups for focusing on the wide-angle side and telephoto [1u].

In this way, in a zoom lens using the rear focusing method, the focusing lens group can be moved between the wide-angle end and the telephoto end zoom position. IIIIMcD running less is
This is important because it does not create wasted space inside the camera, and it also reduces the time it takes to focus.

Furthermore, in order to better achieve the object of the present invention, when the variable power unit zooms from the wide-angle end to the telephoto end, the lens #F is moved toward the object side. It is preferable to perform focusing by moving a part of the lens group whose refractive power on the image plane 0111 is negative from an object at infinity toward the close object K toward the image plane. Wide angle Blfl
When zooming from to the telephoto side, V's! By moving IfF toward the object side with zooming, the difference in the extension position of the focusing lens group is reduced.

Then, a part of the lens group having negative refractive power located at the rear of the lens a+l-" is set to the position 1 for focusing an object at infinity.
If you move the lens to the YC image plane when focusing on a close object from the center of the camera, you can move in conjunction with zooming and use the empty lens space effectively, making the overall length of the lens longer for focusing. There is no need to do this, and the zoom lens system can be made smaller.

In addition, in the present invention, the lens configuration of the zoom lens is such that a positive refractive power is given to the object II rather than the object II, and the lens &'i' V is fixed or moves on the light -11 when changing the magnification.
+, a variable magnification lens &'fV, and a lens 71[0 for correcting the changing image plane.

In this way, the lens group V is placed in front of the variable power lens df■.
By arranging +, the variable power effect of the lens #P v tc can be promoted, the zoom lens can easily be made to have a high variable power, and the K lens system as a whole can be miniaturized while maintaining the desired zoom. ratio can be achieved.

In the zoom lens according to the present invention, in order to maintain the focal length of the entire lens system within an appropriate range.

It is preferable to arrange a lens %R having a positive refractive power between the variable power section and the lens 8tF.

By arranging the lens group R, aberrations can be corrected well over the entire zoom range, and an appropriate back focus can be easily obtained.

History 2 In order to more clearly achieve the object of the present invention, the following conditions are satisfied, where the focal length of the lens group F is flj I, and the focal length of the entire lens system at the zoom position at the telephoto end is k. It is preferable.

When the refractive power of the lens group F is made small so as to satisfy conditional expression (1), the focal length of the entire lens system does not change significantly even if the lens group F is moved in conjunction with zooming. Therefore, the lens g4 is designed so that the extension of the focus section on the telephoto side is convenient for the device that automatically adjusts the focus.
The moving part 1- can be adjusted freely.

When Conditional Expression (1) is not satisfied and the refractive power of lens 4#+F increases, the image point position moves due to zooming, and becomes large enough to be determined as having moved by focus #.

Therefore, it becomes necessary to correct the shape of the moving cam of the lens group C, and the optical performance deteriorates, so it is necessary to correct the aberrations of all the lens threads repeatedly.

In addition, the hologram is generally placed closer to the object than the lens #+F, but if the rupture power of the lens 4+F is larger than formula (1), the aperture diameter may be adjusted to the zoom position. If there is no change, there will be no 7L. It's still a lens j
It is necessary to use the best of the moving members of the cam 4, which are connected to the zooming and move the cams.

That is, if 14 is not added to the equation (0), it is not preferable to correct aberrations of the lens system and change the aperture unit each time the automatic focusing device is adjusted or adjusted.

Also, if J2 is in the unexploded 1st force, lens i + F l"Z '4
It is convenient to use two lens groups with positive and negative refractive powers for one lens 11jl and one lens, and to use a lens Rk 64m for the focus section.
The entire polished zoom lens has been miniaturized, and the motor for driving the focus lens 4; Therefore, it can be easily driven, especially for cameras with automatic focusing device d. Next, numerical examples of the present invention will be shown.

Focus lens extension distance i 5 V lens group composite focal length = -1398, 25m
n+Composite focal length 60.0-142.681U111 Focus lens extension amount 5th lens group Composite focal length 13791.2mm (lol) In Example I, the 1st lens group and 4th lens group are used during zooming. The second lens group is fixed, the second lens group is for zooming, the third lens group is for image plane correction, and the fifth lens group is movable.

In the third embodiment of the equation 1, the Luns solution moves during zooming to promote the variable magnification effect.

#42 lens folding is for zooming, 3rd lens/#F is for edge correction, 4th lens group is fixed during zooming, and focusing is done by moving the folding plate after zooming. ing.

However, in Numerical Example 1.2, 1 tsubo of the fourth lens is not necessarily required.
is fixed during zooming, and the lens configuration is such that focusing is performed using the relay lens of the known 4-group zoom lens, and the object distance is 2yn. The movement of the HtrH5L/lens lens group is 2f5.29mm.With the focusing method of the present invention, the movement of the lens group for ruka focusing is reduced to 40mm by 11.08+n+u.Similarly. In numerical example 2, 24.27 uun is 9.5
According to the focusing method VC of the present invention, the difference in the movement line of the focusing lens group at the wide-angle end and the telephoto end can be reduced, so that the autofocus moonlight is sometimes used. System tζ is suitable. Note: In the lens configuration of the present invention, a fixed lens mainly used for aberration correction may be arranged behind the lens group F.

In addition, in the present invention, lens group Ft-zooming subtraction,
Although the actual example of moving the lens group toward the object side has been shown, the lens group with positive refractive power on the object side is moved toward the image plane side to the object 111! Focusing may be performed by moving # to l.

Furthermore, it goes without saying that the lens group F may be composed of two or more lens groups and focusing may be performed by moving some of the lens groups.

[Brief explanation of the drawing]

Figures 1 and 2 are numerical implementations of the present invention. FIG. 2 is a schematic diagram of the arrangement of the optical system of the valley lens 01 of No. 2; In the figure, arrows indicate the movement state of each lens group due to zooming. In the figure, ■ is a lens group for zooming, 0 is a lens group for image plane correction, %R is a fixed lens group, and F is a lens group that partially includes a focusing lens # that moves during zooming.

Claims (1)

[Scope of Claims] (1) A variable power lens mV having at least one lens group that moves on the optical axis in order to change the focal length across the United States, and a variable power variable lens #V written in Ail by movement. a magnification changing section consisting of a correction lens group 0 having at least I lens groups that move on the optical axis in order to maintain a changed image plane position at a constant position; It is characterized by arranging a lens group F having a small composite refractive power consisting of a nimble lens group that moves integrally in conjunction with the variable magnification action, and focusing by moving a part of the lens #F. How to focus a zoom lens. (2) The variable magnification section zooms from the wide-angle end to the telephoto end (>T. When zooming into the cage, the lens group F is moved toward the object side and the image plane 1111 of lens 1 and 1 is
The zoom according to claim H, wherein focusing is performed by moving a part of the lens group whose refractive power is negative from an object at infinity to a close object in the direction toward the image plane. How to focus the lens. < kJJ tit A focusing method for a zoom lens according to claim 4 or 2, characterized in that the lens is constructed from Paku 001 shell. (4) A focusing method as claimed in claim 1, characterized in that a lens group R having a stop refractive power is arranged in the curve of the variable power section and the lens u+1-. (b) The focal length of the 8U lens xHrr is 1F, and the focal length of all lens threads at the telephoto end zoom position is right. A focusing method for a zoom lens according to claim 3, characterized in that the following conditions are satisfied: (6) The focusing method for a zoom lens according to claim 2, wherein the lens nF is constituted by two lens groups having a focal length and a negative folding power in order from the object side.