JPS5931923A - Focusing method of zoom lens - Google Patents

Abstract

PURPOSE:To reduce unnecessary movement of a focusing lens and to shorten the time up to focusing, and to prevent malfunction by setting a movement trace by zooming and the refracting power of each lens group consistituting a zoom part Z so that while a lens group F is fixed, the image plane position is held constant to a close-distance body. CONSTITUTION:A line QQ' is the position of the lens group F when a close-distance object is in focus, and fixed. The limiting means which inhibits the lens group F for focusing from moving forth beyond a line PP' electrically or by lens barrel structure is provided to limit the movable range of the lens group F to inside of an area sepcified by points P, P', Q', and Q. Then, when zooming is performed from a zoom position Z, i.e. point A to a wide angle side, the lens group F moves in contact with the line PP' and focusing moves from a wide- angle side point B' to a point A'' by an automatic focusing function. Therefore, the unnecessary movement of the lens group for focusing is removed previously to shorten the time necessary for the focusing.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a focusing method for a zoom lens, and more particularly to a so-called rear focusing method in which focusing is performed using a lens group close to an image plane.

In a zoom lens that is generally composed of three or four lens groups, so-called three or four or more lens groups, some of the lens groups at the rear of the lens system and close to the image plane Various so-called rear focusing methods for performing focusing have been proposed. These rear focus methods are most effective when used in the optical system of a camera that has automatic focusing (low capability).In other words, this method allows the focus lens to be smaller and lighter, increasing the focusing speed (~, This is because it is extremely effective in reducing the load on the drive system.However, the above focusing method generally has the following drawbacks.

This will be explained next using figures.

FIG. 1 is an explanatory diagram showing the movement of each lens group in a conventional zoom lens rear focusing method.

In Figure 1, the line PP' indicates the movement trajectory of the variable power lens group, which is located on the object side of the focusing lens, during zooming, and the line PP' indicates the movement of the focusing lens when focusing on a nearby object. Movement trajectory due to zooming, line Q Q
' is the f8 trajectory obtained by zooming when the focus lens is focused on an object at infinity. For example, zoom position 2, where the focus lens is located. Assume that the camera is at point A and is in focus on a predetermined object. Next, when zooming from this state to the wide-angle side, the camera moves to point A'. However, the focus position for a given object is point A', so move the focus lens from point A' to point A''!1B'
There is peace of mind in focusing with J+. 1) In a camera system with automatic focusing device, the motor is driven by the focus detection signal at point A' to move to point A'. Since the region of existence of is the part surrounded by the point p p'Q'c4,04, point A' is outside the region of existence of the focus lens. Therefore, focusing from point A' to A' involves more movement than is originally necessary, which slows down the focusing speed and further causes the level of the focus detection signal at point A' to be zero. Alternatively, there is a possibility that there will be only noise, which may cause the automatic focusing device to malfunction, which is not ideal.

In the so-called zoom lens rear focusing method of the present invention, unnecessary movement of the focus lens is reduced.
The purpose of the present invention is to provide a focusing method for a zoom lens suitable for an automatic focusing function, which shortens the time required for focusing 1 and does not cause malfunctions.

The feature of the zoom lens focusing method for achieving the object of the present invention is that the zoom unit 2 has a lens group for changing magnification and a lens group for correcting fluctuations in the body surface position caused by changing the magnification, and is located closer to the image plane than the zoom unit. Focusing is performed with the lens group F located at , and when the lens group F is focused on a close object, the body surface position is maintained at a constant position even when zooming is performed by moving only the zoom section 2. It is.

In a zoom lens that performs focusing with the lens group 7 located behind the zoom section Z, the zoom section is adjusted so that the image plane position (f'a) is kept constant with respect to a nearby object, with the lens group F in a fixed state. The refractive power and the movement locus for zooming of each lens constituting the second lens are set.

In other words, the movement trajectory of the lens group by zooming to correct the fluctuation of the image plane group caused by zooming is set in a state where the lens group F is focused on the closest object distance. (1) It is possible to eliminate unnecessary movement of the lens group F, and it is also possible to reduce the movement of the lens group F when focusing on a new object distance. At this time, there are the following three methods for moving the lens group y.

The first method is a method in which a lens group for 7 orcuses is directly fed out using a recoid or a cam, etc., and a member having a 4-fluorescence function is provided. In these two methods, the locus of movement of the focusing lens group F with respect to an infinite object is shown by the line PP' in FIG.

FIG. 2 is an explanatory diagram showing the movement state of the lens group in the focusing method of the zoom lens, similar to FIG.

The line QQ' is the valence degree of the lens group F when focused on a close object, and is not in a fixed state. If an electrical or lens barrel structural trap restriction means is set so that the focusing lens group F does not move forward beyond this line PP', the movable range of the focusing lens group F becomes the point p p /
Qr Restricted to the area surrounded by Q. Therefore, when zooming from zoom position 2 of point A toward the wide-angle end, line P
The lens group F moves in contact with P', and focuses from point B' on the wide-angle side to point A' using, for example, an automatic focusing function. Point B' is the focusing position for an infinite object, and the detection signal for automatic focusing is not guaranteed, and compared to the movement of line A'A' shown in FIG. 1 of the conventional example, The moving distance is short. Furthermore, as line Q Q', which is the focusing position for a close-up object, by providing a structural restriction means, the focusing lens group F is moved closer to the image side than line Qct'. Moving quickly improves focusing speed and prevents malfunctions.

Next, the fifth method P, the line P in Figure S shown similarly to Figure 2.
In this method, the shape of P' is determined by providing a cam of lens group F for one low limit object. A member having a retraction function such as a helicoid or a cam can be provided based on the position of this cam.

Lines Q and ct' in Fig. 6 are the focusing addition of the focus lens group to a close object, and the focus lens group F
A step is provided inside the lens barrel to prevent Q Q' from moving backward.

In FIG. 5, when lens group F is at point A, lens group F first moves to point B' for zooming, and then moves from point B' to a point for focusing.

The focusing method of the zoom lens according to the present invention is achieved by the lens configuration described above, but to show a more specific lens configuration, for example, the zoom unit 2 is arranged in order from the object side to the lens group having negative refractive power. and a second lens group having a positive refractive power, and a fifth lens group having a negative refractive power.
Preferably, it is composed of a lens group. Then, with the sixth lens group in a fixed state, the loci of movement of the lens group and the second lens group are set so that the image point position with respect to the close object distance is kept constant.

In this case, a fixed lens group may be arranged in front of the lens group or behind the Vi fifth lens group to obtain a predetermined focal length or back focus.

As described above, according to the present invention, an optical arrangement is adopted in which the focusing lens group does not move 17 with respect to a close-range object,
By employing the above six focusing methods, etc., the movable area of the focusing lens group can be limited to an area where an object can exist. As a result, when performing automatic focusing, for example, it is possible to eliminate in advance the movement of the lens group for focusing, which is difficult, and the time required to achieve focusing can be shortened. In addition, noise signals and erroneous signals generated when the focusing lens group is located in an area where the tube body cannot be present can be removed in advance, which prevents system malfunctions and improves focus performance. It is possible to simplify the filters for preventing erroneous distance measurement provided before and after the circuit, and it is possible to improve focusing by 1°a degree.

Next, a numerical example of an embodiment of the focusing method for a zoom lens according to the present invention will be shown in a case where the zoom lens is configured with six lens groups.

In each embodiment, the focusing lens group is the third lens group B. Further, the movement riL'+ and traces of each lens group during zooming in Example 1.2 are shown in FIGS. 4 and 5, respectively.

Example 1 L: wide-angle end M: middle N: wide-angle end TJ =
2 9.2mN M = 56.6 N = 84.8 Focusing movement amount L: 2. OOm cumulative M: 7.15 N; 15.2 M The closest object distance was 732.55 mm from the image plane.

□□□-Me Example 2 L: Wide-angle end M: Intermediate N: Telephoto end L = 3
5.6 2myr M=59.8O N=84.65 Focusing movement L; 2.48 mm M: 7.0 O N: 13.16 For close objects [# is set at 756.26 mm from the image plane.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of the optical system of a rear focus zoom lens, and FIGS. 2 and 6 are explanatory diagrams of the optical system of the focus port of the zoom lens of the present invention. Each point on the line connecting points Q and Q' in the figure is the in-focus position of the focusing lens group for a close object, and the line connecting points P and P' is the in-focus position for an object at infinity. FIG. 4 is a diagram showing the zoom locus of the first embodiment, and FIG. 5 is a diagram showing the zoom locus of the second embodiment, and the line Qq't is the in-focus position of the lens group for focusing on a close object. B1 in the figure. B2. B5 is a symbol indicating the lens group, the second lens group, and the third lens group, respectively.

Claims (2)

[Claims] (1) A zoom unit 2 having a lens group for changing magnification and a lens group for compensating for changes 1i11 in the image plane position caused by changing magnification.
Even if focusing is performed by the lens group F located closer to the body surface than the zoom section, and zooming is performed by setting only the zoom section Z to Q+ when the lens group F is focused on a close object, the image will not change. A zoom lens focusing method that makes In fP'< that the surface position is maintained at a constant position, (2) The zoom part Z object (consisting of a lens group having a negative refractive power and a lens group having a positive refractive power in order from In+) How to focus a zoom lens.