JPS61259217A - Magnification varying method for zoom lens - Google Patents

Abstract

PURPOSE:To make the whole of a lens system small-sized and to vary the magnification to a high value by providing the first positive lens group, the second negative lens group, and the third positive lens group arranged in order from the object side and providing a stop between the second lens group and the third lens group and fixing the stop or moving it in the direction of the second lens group to execute two magnification varying method with prescribed motions. CONSTITUTION:Refracting powers of the first lens group I and the second lens group II are so set that a luminous flux passing these lens group becomes divergent light, and a stop R11 is fixed and the first lens group I is moved monotonously to the object side and the second lens group II is moved to the image surface side to perform the first magnification varying. When lens groups come to magnification varying positions where image forming relations as a magnification varying system cannot be established in accordance with extension of the first magnification varying or the first lens group I is switched from monotonous movement to reciprocation in case of magnification varying, only the second lens group II or the first lens group I and the second lens group II are moved from the vicinity of the telephoto end of the first magnification varying in accordance with moving loci different from those of the first magnification varying and the stop R11 is moved in the same direction as the second lens group II to perform the second magnification varying.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention relates to a method for changing the magnification of a zoom lens, and in particular to a method for changing the magnification of a zoom lens, which is suitable for use in still cameras, cine cameras, video cameras, etc. The present invention relates to a method for changing the magnification of a zoom lens having a magnification means. More specifically, the first magnification change is performed by changing the focal length in the usual way, and the second magnification change is performed by moving the diaphragm and using a method different from the first magnification change, which reduces the temperature of the entire lens system. The present invention relates to a zoom lens zooming method that can achieve a high zoom ratio.

(Prior art) Conventionally, from the object side, positive, negative, and positive refractive powers are
, has three lens groups, a second lens group and a third lens group, and the third lens group has three lens groups, a second lens group and a third lens group, and the distance between the first lens group and the second lens group is increased, and the distance between the second lens group and the third lens group is decreased. 1. A zoom lens in which magnification is changed by moving the second lens group has been proposed, for example, in Japanese Patent Laid-Open No. 58-199313.

In this zoom lens, the aperture is placed in the fixed third lens group when changing the magnification, and the F number is kept constant throughout the entire magnification range, so the overall lens length is relatively short and aberrations can be corrected. It has the feature that it can be done relatively easily. However, in order to achieve a high variable power with this lens configuration, it was necessary to increase the amount of movement of the second lens group having a variable power function. As a result, the distance between the second lens group and the third lens group increases, and in many cases, the light emitted from the second lens becomes diverging light, so the diameter of the light beam incident on the third lens group increases, and The lens diameter and aperture diameter of the lens group increased, and the entire lens system tended to become Mars-like. Furthermore, since the open F-number is constant, the diameter of the front lens tends to increase as the focal length increases.

One way to reduce the diameter of the front lens is to change the F-number by changing the aperture diameter as well as changing the magnification.

However, in general, changing the aperture diameter is relatively easy when the aperture moves as the magnification changes, but when the aperture is fixed, the interlocking mechanism is complicated and difficult. .

(Objective of the present invention) The present invention employs two methods of variable power, first variable power and second variable power. In the first variable power, the aperture is fixed, and in the second variable power, the aperture is set to the second variable power.
The purpose of the present invention is to provide a method for changing the magnification of a zoom lens, which prevents an increase in the diameter of the aperture by moving the lens group in the same direction as the movement direction of the lens group, and also allows for a high magnification change while reducing the size of the entire lens system. do.

(Main feature of the present invention) Three lens groups: (from the object side) a first lens group with positive refractive power, a second lens group with negative refractive power, a third lens group with positive refractive power, and a second lens. The refractive power arrangement of the first and second lens groups is set so that the light flux passing through the first and second lens groups becomes diverging light, and the aperture is arranged on the image plane side of the lens group. is fixed and the first lens group is monotonically moved toward the object side, and the second lens group is moved toward the image side to perform the first magnification change.When the first magnification change is extended, the magnification change occurs. At the zooming position where the imaging relationship as a system does not hold, or when the lens group shifts to a monotonically increasing reciprocating motion, the lens group moves from the vicinity of the telephoto side of the first zooming to the second zooming position. The second magnification change is performed by moving only the lens group or both the first and second lens groups along a movement locus different from that for the first magnification change, and moving the aperture in the same direction as the movement direction of the second lens group. That's what I did.

Other percentages of the invention are described in the examples.

(Implementation row) FIG. 1 is a schematic diagram of an optical system according to an embodiment of the present invention. (2) in the figure shows the wide-angle end of the first variable magnification, (2) in the figure shows the telephoto end of the first variable magnification, that is, the wide-angle end of the second variable magnification, and O in the figure shows the telephoto end of the second variable magnification. In the figure, 1 is the first lens group with positive refractive power, the antinode is the second lens group with negative refractive power, ■ is the third lens group with positive refractive power,
P is aperture]. Arrows indicate the direction of movement during zooming.

In this example, the composite refractive power of the first lens group and the second lens group is used to cover the entire zooming range of the first and second zooming, and the zooming function of the second lens group is effectively used. It is being demonstrated to the fullest.

In addition, in this embodiment, the first zooming is performed by fixing the diaphragm j5P and moving it monotonically toward the body side of the first lens group Itm, and moving the aperture j5P monotonically toward the body side of the second lens group ■.
This is done by moving the image toward the image plane. By adopting such a zooming method, the overall length of the lens on the wide-angle side of the first zooming is shortened. And the second variable power is the first lens #
The metal object is moved to the object side, and the second lens (detail 2) and the aperture 1) are moved integrally to the Pt image plane side. In this case, the second magnification change is performed at a magnification change position (for example, the first lens The magnification change position is such that the amount of movement of the first lens group or the second lens group becomes infinite) or the magnification change position t't-is where the first lens group shifts from a monotonous increase to a reciprocating motion. In other words, in this embodiment, each lens group is moved to a new variable power area, ie, a second variable power area, by avoiding a position where variable power is not possible or a variable power position where the mechanical structure for variable power is complicated. This effectively expands the zoom range. Then, by moving the diaphragm P in the same direction as the movement direction of the second lens group while keeping the aperture diameter fixed, the F number is changed as the magnification changes, and the diaphragm of the divergent light flux emitted from the second lens group is changed. The diameter of the incident light beam is reduced, and the diameter of the front lens is reduced as the aperture diameter and focal length are increased, while the overall lens system is made smaller.

In this embodiment, the diaphragm P may be moved independently of the second lens, for example, at different moving speeds. According to this, aberration correction can be performed better.

In addition, in this embodiment, normal shooting is carried out over the entire magnification range in the first magnification change, and in the second magnification change, a certain range on the wide-angle side and the telephoto side is taken, except for the range where the above-mentioned magnification change positions are skipped. Alternatively, only the zooming positions at the wide-angle end and the telephoto end may be used.

In this way, the moving cam structure can be made up of linear cams, and the structure can be simplified.

Next, numerical examples of the present invention will be shown. In the numerical implementation sequence,
R1 is the radius of curvature of the first lens surface from the object side,
Di is the thickness of the first lens and the air gap in order from the object side, and Nt and ν1 are the refractive index and Abbe number of the glass of the first lens, respectively, in order from the object side.

Numerical example F=77.6-275 FNO-1: 45-5.4
2ω-3L'-9,σR1-1013201-2-40
N 1-L 80518y 1-2i4R2
-6 & 59 D 2-6.80 N
2 Liao 1.51633 ν 2-6 Table IR3--7
925,45D 3-α10R←147.71D
4-4.00 N B-L 51742 y 3-
5L 4R5--9YUO6D5-(na) R6m-19482D fk= L 40 N 4-
L 80400 y 4-46.6R7-50,28
07-2,67 R8--43,51D8-1.50 N 5-L
77250y 5=49.6R9-3L48
D9-λ50 N 6-L 84666 Shi6-yu 9RIO earthquake-3159,43010-(variable) R
11-(Aperture) Dll-1, 59R12-245,
25Di2-4.00 N 7-L 51835
v7'6α3R13--69,74Di3-0.
10R14-40, 67Di 5.50 N8 polished 1
．． 48749 Shi8-7α2R15--64,55
Di5-1.50 N 9-L 80518
νML 4R16--31400016-0,10R1
7-43,97Di7-5.50 N10=1.4
8749 ylO'70.2R1&--79,4
2Di8-2-00 Ni1-L 80610
yll-4α9R1'l)-179,74Di9
-3138R20-8Z 69 020-5.0ON
12 sho 1.58144 shi 12 sho α7R21--4
0,86D21 3.47R22= -35,72D
22-3.00 N15-L 77250
ν13@a4'iL 6R23--6Z 63 0
23- & 83R -25,69D24-3.0
0 N14-'L 80400 shi1←4&
6R25--66,40 fI-13a77 f■--29,30 fy, -37,22 (Effects of the present invention) According to the present invention, the zoom lens has a predetermined refractive power.
The lens system is configured with two lens groups, and the diaphragm is fixed in the first variable magnification, and the aperture is moved in the second variable magnification. It is possible to achieve a method of varying the magnification of a nine-zoom lens that achieves a high zoom ratio while simplifying the process.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of an optical system according to an embodiment of the present invention, and FIG. 2 is a sectional view of a lens in a numerical implementation of the present invention. In Fig. 1, (8) is the wide-angle end of the first variable magnification, the telephoto end of the first variable magnification and the wide-angle end of the second variable magnification, (0 is the telephoto end of the second variable magnification, t,
n and m are the first, second, and third lens groups, respectively, and P is an aperture.

Claims (1)

[Claims] Three lens groups, in order from the object side: a first lens group with positive refractive power, a second lens group with negative refractive power, a third lens group with positive refractive power, and the second lens group. a diaphragm disposed closer to the image plane, and the refractive power arrangement of the first and second lens groups is set so that the light flux passing through the first and second lens groups becomes diverging light; A first magnification change is performed by fixing the aperture, moving the first lens group toward the object side in a monotonous manner, and moving the second lens group toward the image plane side.
When the zooming is extended, the zooming position where the imaging relationship as a zooming system no longer holds true, or the zooming position where the first lens group shifts from a monotonous increase to a reciprocating motion during zooming is interposed, and the first zooming is started. From near the double telephoto side, only the second lens group or both the first and second lens groups are moved along a movement trajectory different from the first magnification changer, and the aperture is moved in the direction of movement of the second lens group. A method for changing the magnification of a zoom lens, characterized in that the magnification is changed by moving the lens in the same direction.