JP2000105337A - Zoom lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a compact zoom lens for a solid-state image pickup element whose entire length at a short focus end is short, whose diameter is small and which is hardly influenced by an error. SOLUTION: This lens is constituted of a 1st lens group having a positive focal distance, a 2nd lens group having a negative focal distance, and a 3rd lens group having the positive focal distance from an object side. The 1st lens group and the 2nd lens group are moved to the object side along an optical axis so that space between the 1st lens group and the 2nd lens group may be decreased and space between the 2nd lens group and the 3rd lens group may be increased in the case of performing variable power from the short focus end to a long focus end. In such a case, a conditional expression 1.1<fb1/f1<2.5 (in the expression, f1 means the focal distance of the 1st lens group and fb1 means the back focus of the 1st lens group) is satisfied.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a zoom lens, and more particularly, to a compact zoom lens having a zoom ratio of about 2 to 3 which is suitable for an electronic still camera using a solid-state image pickup device such as a CCD or a video camera. About the lens.

[0002]

2. Description of the Related Art In recent years, software for handling image data has been remarkably developed along with the technical progress and spread of personal computers, and there has been an increasing demand for electronic still cameras used for reading images into personal computers.

As a zoom lens for a solid-state image pickup device,
(A) There is a two-group configuration in which a negative lens group and a positive lens group are arranged from the object side and the distance between these groups is changed to change the magnification, or a three-group zoom lens is disclosed in JP-A-10-1331.
The technology is disclosed in Japanese Patent Publication No. 15 and the like. (B) Japanese Patent Laid-Open No. 2-291 discloses a zoom lens having a three-group or four-group configuration in which a positive lens group, a negative lens group, and a positive lens group are arranged from the object side.
The technology is disclosed in, for example, Japanese Patent Publication No. 515.

[0004]

However, (a)
As seen in Japanese Patent Application Laid-Open No. H10-133115, the overall length of the lens, that is, the distance from the first lens surface to the image forming surface, tends to be longer at the short focal length end having a large angle of view. In addition, the diameter of the lens closest to the object is large. In the zoom lens having the configuration shown in FIG.
As seen from Japanese Patent No. 291515, the entire length of the lens is not changed at the time of zooming, so that the overall length of the lens at the short focal length end is also small, and the diameter of the lens closest to the object is the largest.

[0005] As a zoom lens having a short overall length at the short focal length end, a conventional zoom lens for a silver halide film camera is known. Necessary low-pass filters and the like cannot be arranged behind the zoom lens. In addition, there is a problem in that errors such as lens group spacing and eccentricity have a large effect on photographing performance, making it difficult to manufacture.

The present invention has been made in view of the above problems, and an object of the present invention is to reduce the overall length of the lens at the short focal length end,
An object of the present invention is to provide a small-sized zoom lens for a solid-state imaging device having a small lens diameter and hardly affected by an error.

[0007]

The above object is achieved by any of the following means.

(1) From the object side, a first lens unit having a positive focal length, a second lens unit having a negative focal length, and a third lens unit having a positive focal length are provided. At the time of zooming from to the long focal end, the distance between the first lens group and the second lens group is reduced, and the distance between the second lens group and the third lens is increased so that at least the first lens group and the third lens group are moved. A zoom lens in which two lens groups move to the object side along the optical axis, wherein the following conditional expression is satisfied.

1.1 <f _b1 / f ₁ <2.5 (1) where f _{1 is} the focal length of the first lens group f _{b1 is} the back focus of the first lens group (2) The following conditional expression is satisfied: (1)
A zoom lens according to claim 1.

1.0 <f _W / f ₁ <1.3 (2) where f _{W is} the focal length of the entire system at the short focal length end. Characterized by satisfaction (1)
Or the zoom lens according to (2).

1.6 <f _T / f ₁ <3.0 (3) where f _{T is} the focal length of the entire system at the long focal length end. Inside the first lens group or the first
The zoom lens according to (1), (2) or (3), wherein the zoom lens is arranged on the image side of the lens group and is moved together with the first lens group at the time of zooming, and satisfies the following conditional expressions.

0.3 <f _W / f ₃ <0.8 (4) where f _{3 is} the focal length of the third lens group. (5) The third lens group is variable. The zoom lens according to any one of (1) to (4), wherein the zoom lens does not move during magnification.

If the upper limit of conditional expression (1) is exceeded, the total lens length at the short focal length end becomes longer, the refractive power of the negative lens in the first lens group increases, and the Petzval sum becomes undesirably large. If the lower limit is exceeded, the back focus at the short focal length end becomes short, the space becomes small when a low-pass filter or the like is inserted behind the lens, or the exit pupil position of the lens becomes close to the image plane, and the CCD becomes
This is not preferable when using a solid-state imaging device such as

When the value exceeds the upper limit of the conditional expression (2), when the zooming magnification ratio is increased, errors such as lens thickness, spacing, and eccentricity at the long focal length end greatly affect the imaging performance. Become. Therefore, it is difficult to obtain a sufficient zooming.
Therefore, application to a lens for a high-resolution solid-state imaging device having a small pixel pitch is particularly difficult. On the other hand, if the lower limit is exceeded, the refractive power of the first lens group becomes small, and the Petzval sum becomes negative and large, so that the image plane cannot be made flat.

If the upper limit of conditional expression (3) is exceeded, the above-mentioned error at the long focal length end is undesirably large. On the other hand, when the value exceeds the lower limit, the zoom lens has a low zoom ratio, which is not preferable.

Further, an aperture stop is arranged inside the first lens unit or on the image side of the first lens unit, and is moved together with the first lens unit at the time of zooming, so that the refractive power of the third lens unit is determined by the conditional expression (4).
Is satisfied, the exit pupil position can be appropriately set in all the zoom states. If the upper limit of conditional expression (4) is exceeded, the third
The refractive power of the lens group is too large, the axial thickness of the third lens group becomes large, and the back focus at the short focal length end becomes undesirably small. On the other hand, if the lower limit is exceeded, the angle of incidence of the light beam incident on the peripheral portion of the screen at the short focal length end becomes too large.

If the third lens group is configured not to move during zooming, the third lens group can be fixed together with the rear low-pass filter, and the structure is simplified.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the zoom lens according to the present invention will be described below, but the present invention is not limited thereto.

Here, the symbols used in each embodiment are as follows.

F _No : F number ω: Half angle of view R: Curvature radius of refraction surface D: Distance between refraction surfaces N _d : Refraction index at d-line of lens material ν _d : Abbe number of lens material f ₁ : First F ₃ : focal length of the third lens group f _b1 : back focus of the first lens group f _w : focal length of the entire system at the short focal length end f _T : focal length of the entire system at the long focal length end (Embodiment 1) FIG. 1 is a sectional view of the optical axis of Embodiment 1 and the movement locus of each lens unit during zooming. Tables 1 and 2 show lens data.

[0021]

[Table 1]

[0022]

[Table 2]

FIG. 2 shows (A) the short focal length end and (B) of the first embodiment.
It is a lens aberration figure in an intermediate | middle, (C) long focal point.

The third lens group comprises a single lens,
Although it does not move at the time of zooming, it may be composed of a plurality of lenses or may move slightly in the optical axis direction at the time of zooming.

Although all lenses are composed of spherical lenses, better results can be obtained by using aspherical surfaces.
In particular, when used for a positive lens disposed in the rear half of the first lens group, spherical aberration and the like can be corrected well.

(Embodiment 2) FIG. 3 is a sectional view of the optical axis at the short focal length end of Embodiment 2. Table 3 shows the lens data.
It is shown in FIG.

[0027]

[Table 3]

[0028]

[Table 4]

FIG. 4 shows (A) the short focal length end and (B) of the second embodiment.
It is a lens aberration figure in an intermediate | middle, (C) long focal point.

In the second embodiment, the third lens group is constituted by a single lens, and does not move at the time of zooming. However, even if it is constituted by a plurality of lenses, or it moves slightly in the optical axis direction at the time of zooming. You may.

Although all lenses are composed of spherical lenses, better results can be obtained by using an aspherical surface.
When used for a positive lens disposed in the rear half of the first lens group, spherical aberration and the like can be corrected well.

[0032]

The zoom lens according to the present invention has the following advantages because it is constructed as described above. A small zoom lens with the smallest effective lens diameter on the object side and good correction of lens aberration was obtained.

Also, since the entire length of the lens can be shortened at the short focal length end having a large angle of view, even if a separate finder optical system is mounted with a small distance from the optical axis of the zoom lens,
The field of view is hard to be seen by the zoom lens, and the zoom lens is suitable for a compact camera with small parallax.

Also, a sufficient back focus can be obtained at the short focal length end, a low-pass filter or the like can be inserted behind the lens, and a compact zoom lens for a solid-state imaging device can be obtained.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of an optical axis according to a first embodiment and a movement locus of each lens group during zooming.

FIG. 2 shows (A) a short focal length end, (B) an intermediate position,
FIG. 3C is a lens aberration diagram at the long focal end.

FIG. 3 is a sectional view of an optical axis at a short focal length end according to a second embodiment.

FIG. 4 shows (A) a short focal length end, (B) an intermediate position,
FIG. 3C is a lens aberration diagram at the long focal end.

[Explanation of symbols]

 Reference Signs List 1 1st surface 2 2nd surface 3 3rd surface 4 4th surface 5 5th surface 6 6th surface 7 7th surface 8 8th surface 9 9th surface 10 10th surface 11 11th surface 12 12th surface 13th 13th surface 14th surface 15 15th surface 16 16th surface 17 17th surface 18 18th surface 19 19th surface 20 20th surface 21 21st surface 22 22nd surface CG cover glass

Claims (5)

[Claims] 1. A first lens having a positive focal length from an object side.
The zoom lens system includes a lens group, a second lens group having a negative focal length, and a third lens group having a positive focal length. A zoom lens in which at least the first lens group and the second lens group move to the object side along the optical axis so that the distance between the lens groups decreases and the distance between the second lens group and the third lens increases. A zoom lens characterized by satisfying the following conditional expression. 1.1 <f _b1 / f ₁ <2.5 where f ₁ : focal length of the first lens group f _b1 : back focus of the first lens group 2. The zoom lens according to claim 1, wherein the following conditional expression is satisfied. _{1.0 <f W / f 1 <} 1.3 where, f _W: focal length of the entire system at the short focal end 3. The zoom lens according to claim 1, wherein the following conditional expression is satisfied. 1.6 <f _T / f ₁ <3.0 where f _{T is} the focal length of the entire system at the long focal end. 4. An aperture stop is arranged inside the first lens group or on the image side of the first lens group and is moved together with the first lens group during zooming, so that the following conditional expression is satisfied. The zoom lens according to claim 1, 2, or 3, wherein _{0.3 <f W / f 3 <} 0.8 where, f _3: the focal length of the third lens group 5. The zoom lens according to claim 1, wherein the third lens group does not move during zooming.