JPS5974524A - Focusing method of zoom lens - Google Patents

Abstract

PURPOSE:To make a zoom lens compact, by fixing the first lens group having a positive refracting power and moving the second lens group having a positive refracting power and allowing extents of movement of two lenses of the second group to satisfy a specific conditional expression in case of zooming. CONSTITUTION:In case of zooming, the fixed first lens group having a positive refracting power and the second lens group which is arranged at the rear of the first lens group and has a positive refracting power are moved toward an object and are focused to the close-distance object. At this time, the direction of extension from an infinity object to the closest-distance object is always constant during zooming and is the direction toward the object and is not discontinuous halfway. Though the quantity of extension of the second lens group is increased according as zooming to the telephoto side, the quantity of extension is reduced considerably because the focusing interval is increased, and thus, the zoom lens is made compact. If an expression is satisfied when extents of movement of two lenses of the second group are denoted as (s) and (t) respectively, the zoom lens is made compact also.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a zoom lens using a focusing method,
In particular, the present invention relates to a rear focus zoom lens in which three lens groups are moved to perform zooming, and the first lens group counting from the object side performs focusing.

Conventionally, various methods have been proposed for performing focusing using a zoom section or a fixed lens group located toward the image plane side of the zoom section.

However, in these focusing methods, when focusing on the same object distance, the amount of extension of the focus section is different υ due to the difference in focal length due to zooming, and the amount of extension changes quadratic or discontinuously. Therefore, when the object distance differs, the amount of movement of the focus section will increase by 2.
Next, the curved shape becomes different. Therefore, it is extremely complicated and extremely difficult to mechanically construct a structure that satisfies the amount of focal length extension in the entire zoom range with the same rotation angle of the distance adjusting ring. This tendency becomes more pronounced as the zoom ratio increases.

Next, using a conventional four-group zoom lens as an example, the amount of movement of the focus section when focusing is performed with each lens group will be shown using FIG.

The focal length f of each lens of the zoom lens shown in FIG.
f2. ! ,,! Principal point distance between 4 and each lens group: 11°12
, ls and the focal length f of the zoom lens are as follows.

f1 to 4: Focal length of each lens group 11 to S: Principal point distance between each lens group. Focusing on the Luns group has been widely practiced in the past, as shown in Figure 1(b).
As shown in FIG. 2, during zooming, the amount of extension is constant for the same object distance at all zoom positions. However, when focusing is done with the lens groups after the second lens group, as shown in Figure 1 (
C).

('l) It differs as shown in (e).

The second lens group changes from a reduction system to an enlargement system during zooming, and passes through the same magnification on the way. Therefore, since the second lens group has a negative power, it is extended toward the object side in the reduction system region, and toward the image plane side in the enlargement system region. It becomes discontinuous as shown in 0).

In the case of the third lens group shown in FIG. 1(d), since this conventional example forms an afocal system with the zoom section (first to third lens groups), when the object distance becomes short, Since the paraxial light beam emerging from the fifth lens group becomes a diverging system (in this case, the groups become an expanding system with a positive sign), in order to return it to a parallel light beam, the third lens group is moved toward the image plane side. Just let it out.

In the case of the fourth lens group shown in FIG. 1(e), since the parallel light beam is incident on the fourth lens group as in the case of the fourth lens group, it is sufficient to extend it toward the object side. However, since the afocal magnification of the zoom section increases or decreases during zooming, the amount of extension when zooming differs. In this case, the amount of extension of the fourth lens group is proportional to the square of the afocal magnification.

Also, as the distance to the object becomes shorter (from 5 m to 2 m), the curve of the quadratic curve becomes tighter.

Therefore, in the above-mentioned zoom configuration, in order to perform focusing with the lens units after the second lens group, it is necessary to use a three-dimensional cam whose quadratic curve of the amount of extension due to zooming changes continuously for different object distances. must be used.

(When the rotation angle of the distance adjustment ring is set to be the center of zooming at the same object distance) Or, the lens system is equipped with a mechanism such as an arithmetic circuit, or a TTL autofocus mechanism is provided to electrically focus. It is necessary to calculate the feeding amount of the part.

SUMMARY OF THE INVENTION An object of the present invention is to provide a focusing method for a zoom lens that is advantageous for making the zoom lens more compact by significantly reducing the amount of extension of the focus section when focusing at a close distance at the telephoto end zoom position.

The lens configuration for achieving the object of the present invention is characterized by a zoom lens having two lens groups: a first lens group that is fixed during zooming (from the object side), and a zoom group that has at least three lens groups that move during zooming. In the lens, focusing is performed by moving the second lens group closest to the object among the three lens groups in the zoom group. More preferably, zooming is performed by moving two lens groups on the object side among the lens groups of the zoom group in the same direction.

Therefore, in the zoom lens focus sync method of the present invention, in order to make the zoom lens more compact and to reduce the movement of the lens group for focusing, the first lens group has a positive refractive power and the zoom group has a positive refractive power. It consists of a second lens group with positive refractive power, a 22nd lens group with negative refractive power, and a 23rd lens group with positive or negative refractive power in order from the side. The amount of movement due to zooming is
, t, it is preferable to satisfy the following condition: 0.1<-<1.2 threat...■.

The lens configuration of the zoom lens of the present invention includes a first lens group with a positive refractive power that is fixed during zooming, and a zoom group placed behind it that moves toward the image side when zooming from the wide-angle side to the telephoto side zoom position. A second lens group having a positive refractive power is disposed, and by moving the second lens group toward the object, focusing is performed on a close object. Therefore, when a ray from an object at infinity is incident on the first lens group and paraxial tracking is performed on each lens group, the ratio of the incident angle α to the second lens group and the exit angle α′ (α/α′) is smaller than 1 for positive values in the zooming center. For this reason, when focusing is performed using the second lens group, the direction of movement from an object at infinity to an object at a close distance is constant at the zoom center and becomes the object side direction. As described above, according to the present invention, unlike the conventional example, discontinuity does not occur during zooming.

Furthermore, the amount of extension of the second lens group for focusing at the same object distance increases as the zoom position is zoomed from the wide-angle side to the telephoto side. Since the distance from the second lens group also increases, it is sufficient to secure an air gap for seven focusing that corresponds to the amount of extension at the wide-angle end.

Therefore, there is less wasted space in the optical system of the zoom lens, and the zoom lens can be made compact (1).

Furthermore, as shown in the first embodiment of the present invention described later, the amount of movement of the focusing unit from an object at infinity to an object distance of 2 m is 2.4 degrees at the wide-angle end zoom position and 3.6 degrees at the telephoto end zoom position. Yes, the ratio is 1.5, which is less than the square of this square, which is 8.16. In addition, in the second embodiment described later, since 8 and t are the same value, the same zoom cam can be used to move the second lens group and the 22nd lens group, so the zoom cam of the 25th lens group It is a good idea to use two cams for zooming), and the mechanical structure can be simplified.

The amount of movement of the focusing unit from an object at infinity to an object distance of 1.5 m is the square of the zoom ratio even if it is 5.85vrm at the zoom position at the wide-angle end and 3.2 at the telephoto end. In comparison, it is considerably less.

In addition, in the zoom lens of the present invention, since the light beam once converged by the first lens group with positive refractive power is incident on the second lens group, the effective diameter of the second lens group is smaller than that of the first lens group. It is getting smaller. Therefore, the thickness of the lens may be small, and the weight can be significantly reduced compared to the first lens group, and compactness can be achieved very well. The zoom lens is made more compact by setting the ratio of the amount of movement of the second lens group and the 22nd lens group by zooming so that the above conditional expression (2) is satisfied.

If the upper limit of conditional expression (2) is exceeded, the distance between the second lens group and the 22nd lens group becomes too wide at the zoom position at the wide-angle end, which is undesirable as it leads to an increase in the overall length of the lens. or,
If it is smaller than the lower limit, the first
The distance between the Luns group and the second Luns group is that wide.17i
Although the difference is decreasing, the lens effective diameter of the second lens group is not much smaller than that of the first lens group, and making the zoom lens much lighter in weight results in a conical shape.

The refractive power of the 22nd lens group of the zoom lens according to the present invention is negative, and the moving direction of magnification change for zooming is set to the rear, thereby effectively using the distance between the lens groups to achieve compactness. Further, the fourth lens group is moved along with zooming in order to compensate rE for the image surface that changes due to zooming, and its refractive power is set to be positive or negative, and is moved appropriately depending on the sign of the refractive power.

In the zoom lens according to the present invention, a fifth lens group for imaging having a positive refractive power may be added behind the zoom group.

tl) Adding three lens groups makes it easier to better correct aberrations over the entire zoom range. Further, by arranging a fourth lens group having a negative refractive power behind the third lens group, it becomes easy to maintain a good overall Petzval sum, and a high-performance zoom lens can be achieved.

Next, numerical examples of a zoom lens in the zoom lens focusing method of the present invention will be shown.

fl is the focal length of the first lens group from the object side,
11 is a space between the first lens group and the 1st+1st lens group.

The lens configuration of Numerical Example 1 is shown in FIG. 2, the amount of lens movement due to focusing is shown in FIG. 6, the lens configuration of Numerical Example 2 is shown in FIG. 4, and the amount of lens movement due to focusing is shown in FIG. 5.

Numerical Example 1 E+ .: Focal length of each lens group, el...5
: Principal point spacing of each lens group, F, Coco-6, Go, 4 Numerical Example 2 f2, 7, l, 22. J! , A, '7: Focal length of each lens group, el...5: Principal point interval of each lens group,

[Brief explanation of drawings]

Figure 1 (a) is a schematic diagram of a conventional 4-group type zoom lens, (a) Figures 1 (b) to (e) are explanations of the amount of movement due to focusing by each lens group of the zoom lens in Figure 1. Figures 2 and 4 are schematic diagrams of optical systems of numerical embodiments 1 and 2 of the zoom lens according to the present invention, and Figures 2113 and 5 are numerical embodiments 1 of the zoom lens according to the present invention, respectively. , 2 is an explanatory diagram showing the movement of the lens group due to focusing. Patent Applicant Canon Co., Ltd. Agent Gi Marushima - 5 = ZQ, d f = : 15 91
．． 4th Lens Edge Amount (Skin)

Claims (1)

[Scope of Claims] (1) A zoom lens having two lens groups: a first lens group that is fixed during zooming and a zoom group that has at least three lens groups that move during zooming, viewed from the object side at 11; A zoom lens focusing method characterized by: performing focusing by moving a second lens group closest to the object out of the three lens groups. (2) Zooming is performed by moving two lens groups on the object side among the lens groups of the zoom group in the same direction. . (3) The first lens group has a positive refractive power, and the zoom group includes, in order from the object side, a second lens group with a positive refractive power, a 22nd lens group with a negative refractive power, and a positive or negative refractive power. second refractive power
It has 3 lens groups, and has a 3rd lens group that is fixed during zooming behind the zoom section, and the 2nd lens group and the 22nd lens group move only in one direction during zooming. 2. The zoom lens focusing method according to claim 1, wherein the zoom lens focusing method satisfies the following condition: 0.1<-<L2, where the amount of movement is s and t, respectively.