JP2003161884A - Afocal zoom lens - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an afocal zoom lens having a large magnification and preventing a vignette of light flux from an object point on the optical axis and an object point off the optical axis. <P>SOLUTION: The afocal lens is constituted of a first lens group G1 having negative refractive power, a second lens group G2 having positive refractive power, a third lens group G3 having negative refractive power, a fourth lens group G4 having negative refractive power and a fifth lens group G5 having positive refractive power sequentially disposed from the object. Zooming is implemented by moving the positions of the second, third and fourth lens groups G2, G3, G4 in the direction of an optical axis. An entrance pupil EP of the afocal zoom lens is formed at a front position apart from the first lens group G1. The positions of a projection pupil of an objective lens placed in the front of the afocal zoom lens and the entrance pupil of the afocal zoom lens can be made to coincide with each other. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an afocal zoom lens which is arranged after an objective lens system having a fixed focus and performs zooming, and an optical apparatus using the afocal zoom lens.

[0002]

2. Description of the Related Art In using a microscope, it is necessary to enlarge or reduce an object without changing its objective lens in order to observe the object efficiently. Thus, as an afocal zoom lens used for the purpose of changing the image magnification without exchanging the objective lens,
JP-B-6-77104 and JP-A-5-17307.
Those described in No. 9 are known.

[0003]

However, the afocal zoom lens disclosed in Japanese Patent Laid-Open No. 173079/1993 has a zoom ratio of about 4 times, which is not sufficient. Furthermore, Japanese Patent Publication 6-77104
In the conventional afocal zoom lens as described in Japanese Patent Application Laid-Open No. 5-173079,
It is difficult to make the exit pupil of the objective lens system and the entrance pupil of the zoom system coincide with each other, and as a result, there is a problem that light at an off-axis object point is defocused during zooming.

That is, in most cases, the exit pupil of the objective lens system is located inside the objective lens system. Therefore, in order to actually make the exit pupil of the objective lens system and the entrance pupil of the zoom system coincide with each other, it is desirable that the entrance pupil is located at a position apart from the front side of the zoom system to some extent and that the position does not change during zooming.

The present invention has been made in view of such a situation, and at high magnification, not only the light flux from the on-axis object point but also the light flux from the off-axis object point is less likely to be eclipsed during zooming. , To provide an afocal zoom lens.

[0006]

A first means for solving the above-mentioned problems is to combine, in order from the object side, a first lens group having a positive or negative refractive power and a positive first group negative second group. And a fifth lens group having a positive refracting power, and a lens group having a positive refracting power among the second, third, and fourth lens groups. Has a role of receiving the divergent light and converging the emitted light, and when zooming from the low magnification end state to the high magnification end state or from the high magnification end state to the low magnification end state, the second lens group and the third lens group And a fourth lens group moves along the optical axis. This is an afocal zoom lens (claim 1).

In the present means, the lens group is made up of the five lens groups as described above, so that the entrance pupil can be moved to the first position.
It is possible to put it outside the front of the lens group, and it is possible to fix the position of the entrance pupil, or to make it not change much. Therefore, when it is combined with a fixed focus type objective lens system, the positions of the exit pupil of the objective lens system and the entrance pupil of the zoom system can be made to coincide with each other or both can be brought close to each other. Therefore, at a high magnification, it is possible to prevent not only the light flux from the on-axis object point but also the light flux from the off-axis object point from being eclipsed during zooming. Further, since the number of lens groups is 5, it becomes easy to correct aberrations even at high magnification, and a zoom lens with high accuracy can be obtained.

A second means for solving the above problems is
The first means is characterized by satisfying the following expression (1) (claim 2). | Fm1 / fm2 | <1.8 (1) where fm1 and fm2 are the focal lengths of the second, third, and fourth lens groups having negative refractive power, respectively, and | fm1 | ≧ | Each is selected so that fm2 |.

In this means, the conditional expression (1) is
2 having negative refracting power among the second, third, and fourth lens groups
It defines an appropriate ratio of the focal lengths of the two lens groups. Second,
Of the third and fourth lens groups, at least one of the two lens groups having negative refracting power needs to function as a variator during zooming, but in order to realize a high zoom ratio, It is desirable that the power of this lens group be large to some extent. However, when the value of | fm1 / fm2 | is 1.8 or more, the power becomes too tight, and it becomes difficult to correct the aberration variation during zooming.

A third means for solving the above problems is
The first means or the second means further satisfies the following expression (2) (claim 3). 1.5 <| fp / fm2 | <3.5 (2) Here, fp represents the focal length of the lens group having a positive refractive power among the second, third, and fourth lens groups.

In this means, the conditional expression (2) is
An appropriate ratio of the focal lengths of the lens group having a positive refractive power among the second, third and fourth lens groups and the lens group having a negative refractive power among the second, third and fourth lens groups Stipulate.

If | fp / fm2 | is 3.5 or more, the total length of the zoom lens becomes too long when a desired zoom ratio is obtained, which is not preferable. Also, | fp / fm2 |
If it is 1.5 or less, the power of the lens unit having a positive refractive power among the second, third, and fourth lens units becomes too tight, which is not preferable for aberration correction.

A fourth means for solving the above problems is
Any one of the first to third means, further characterized in that the entrance pupil position is fixed at a position 35 mm or more in front of the vertex of the first lens (claim) Item 4).

Particularly in a microscope, unless the distance from the position of the exit pupil of the objective lens system to the first lens of the afocal zoom lens is at least 35 mm or more, both lens systems often interfere positionally. . In this means, since the entrance pupil position is fixed at a position 35 mm or more in front of the apex of the first lens, the exit pupil of the objective lens system and the entrance pupil position of the afocal zoom lens can be matched. During zooming, not only the light flux from the on-axis object point but also the light flux from the off-axis object point is not eclipsed.

The fifth means for solving the above-mentioned problems is as follows.
An optical apparatus (claim 5), characterized in that the optical system includes the afocal zoom lens according to any one of the first to fourth means.

In the present means, zooming is performed by the afocal zoom lens of any one of the first to fourth means, so that not only the light flux from the on-axis object point at high magnification but also the zooming is performed. It is possible to make it difficult for the light flux from the off-axis object point to be eclipsed. Typical examples of the optical device include a microscope and an inspection device.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, an example of an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing an example of a basic configuration of an optical device using an afocal zoom lens, which is an example of an embodiment of the present invention, in which 1 is an object, 2 is an objective lens, and 3 is an object of the present invention. Focal zoom lens, 4
Is the image forming lens, 5 is the image position, EP is the exit pupil of the objective lens and the entrance pupil position of the afocal zoom lens.

The light emitted from the object 1 passes through the objective lens 2, is zoomed by the afocal zoom lens 3, and is imaged at the image position 5 by the imaging lens 4. When the afocal zoom lens of the present invention is used, the entrance pupil of the afocal zoom lens 3 can be made to coincide with the exit pupil of the objective lens 2 as in this example, and a light beam from an off-axis object point can be blocked during zooming. It can be lost.

FIG. 2 shows a lens configuration in a first example of the afocal zoom lens according to the embodiment of the present invention. The first lens group G having a negative refractive power in order from the object
1, a second lens group G2 having a positive refractive power, a third lens group G3 having a negative refractive power, a fourth lens group G4 having a negative refractive power, and a fifth lens group having a positive refractive power. The lens group G5. Zooming is performed by moving the positions of the second lens group G2, the third lens group G3, and the fourth lens group G4 in the optical axis direction. As shown in the figure, the entrance pupil EP of this afocal zoom lens is formed at a front position away from the first lens group G1.

FIG. 3 shows the lens structure of a second example of the afocal zoom lens according to the embodiment of the present invention. The first lens group G having a positive refractive power in order from the object
1, a second lens group G2 having a negative refractive power, a third lens group G3 having a positive refractive power, a fourth lens group G4 having a negative refractive power, and a fifth lens group G4 having a positive refractive power. The lens group G5. Also in this example, the entrance pupil EP of this afocal zoom lens is formed at a front position apart from the first lens group G1.

[0021]

EXAMPLES Example 1 An afocal zoom lens having a lens system configured as shown in FIG. 2 was designed. Table 1 below lists specifications of the afocal zoom lens of the first example. In the table, f is a combined focal length of the afocal zoom lens and the imaging lens shown in Table 3. As can be seen from the table, the distance from the entrance pupil to the first lens is 35 mm.

[0022]

[Table 1]

4 to 6 are diagrams showing various aberrations when the afocal zoom lens of this embodiment and the imaging lens of Table 3 are used. In each figure, (a) is spherical aberration, the horizontal axis represents the optical axis direction position with the Gaussian image plane position being 0, and the vertical axis represents the F number of the lens system. (B) is astigmatism, the horizontal axis shows the position along the optical axis with the Gaussian image plane position at 0, and the vertical axis shows the image height (mm). (C) is chromatic aberration of magnification, in which the horizontal axis indicates the position in the direction perpendicular to the optical axis, and the vertical axis indicates the image height (mm). Further, (d) shows meridional aberration, (e) shows sagittal aberration, and (f) shows distortion aberration at the image height positions shown in (b).

In the figures showing the following aberrations, the solid line is the d line (λ = 587.56 nm), the broken line is the C line (λ = 656.28 nm),
The one-dot chain line is the F line (λ = 486.13 nm), and the two-dot chain line is the g line (λ =
435.84 nm).

FIG. 4 is a low magnification end state, FIG. 5 is a middle magnification state, and FIG.
Shows various aberrations in the high magnification end state. As is clear from the figure, in this example, various aberrations are satisfactorily corrected from the low magnification end state to the high magnification end state.

(Example 2) An afocal zoom lens having a lens system configured as shown in FIG. 2 was designed. Table 2 below lists specifications of the afocal zoom lens of the second example. In the table, f is a combined focal length of the afocal zoom lens and the imaging lens shown in Table 3. As can be seen from the table, the distance from the entrance pupil to the first lens is 35 mm.

[0027]

[Table 2]

7 to 9 are diagrams showing various aberrations when the afocal zoom lens of this embodiment and the imaging lens of Table 3 are used. The meanings of the figures and the axes of the graphs correspond to FIGS. 4 to 6, respectively.

FIG. 7 is a low-magnification end state, FIG. 8 is a medium-magnification state, and FIG.
Shows various aberrations in the high magnification end state. As is clear from the figure, in this example, various aberrations are satisfactorily corrected from the low magnification end state to the high magnification end state.

Since the afocal zoom lens of each of the above-mentioned embodiments is of the infinity correction type, it is used together with the imaging lens. Table 3 shows the specifications of the imaging lens system used in combination in the calculations of the above-described examples.

[0031]

[Table 3]

[0032]

As described above, according to the present invention,
It is possible to provide an afocal zoom lens which has a high magnification and which is not likely to be eclipsed by not only the light flux from an on-axis object point but also the light flux from an off-axis object point during zooming.

[0033]

[Brief description of drawings]

FIG. 1 is a diagram showing an example of a basic configuration of an optical device using an afocal zoom lens, which is an example of an embodiment of the present invention.

[0034]

FIG. 2 is a diagram showing a lens configuration in a first example of an afocal zoom lens that is an embodiment of the present invention.

[0035]

FIG. 3 is a diagram showing a lens configuration in a second example of the afocal zoom lens that is an embodiment of the present invention.

[0036]

FIG. 4 is a diagram showing various aberrations when the afocal zoom lens of Embodiment 1 and the imaging lens shown in Table 3 are used, and is for a low magnification zoom.

[0037]

5A and 5B are diagrams showing various aberrations when the afocal zoom lens of Example 1 and the imaging lens shown in Table 3 are used, and are for medium magnification zoom.

[0038]

FIG. 6 is a diagram showing various aberrations when the afocal zoom lens of Example 1 and the imaging lens shown in Table 3 are used, and is for a high-magnification zoom.

[0039]

FIG. 7 is a diagram showing various aberrations when the afocal zoom lens of Example 2 and the imaging lens shown in Table 3 are used, and is for a low magnification zoom.

[0040]

8A and 8B are diagrams showing various aberrations when the afocal zoom lens of Example 2 and the imaging lens shown in Table 3 are used, and are for a medium magnification zoom.

[0041]

FIG. 9 is a diagram showing various aberrations when the afocal zoom lens of Embodiment 2 and the imaging lens shown in Table 3 are used, and is for high magnification zoom.

[0042]

[Explanation of symbols]

1 ... Object 2 ... Objective lens 3 ... Afocal zoom lens 4 ... Image forming lens 5 ... Image position G1 ... First lens group G2 ... Second lens group G3 ... Third lens group G4 ... Fourth lens group G5 ... Fifth Lens group EP: exit pupil position of objective lens, entrance pupil position of afocal zoom lens

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Claims (5)

[Claims] 1. A second lens unit, a third lens unit, and a fourth lens unit each including a combination of a first lens unit having a positive or negative refracting power and a positive first unit and a negative second unit in order from the object side, and a positive refracting power. And a fifth lens group having
Among the lens groups, the lens group having a positive refracting power has a role of receiving divergent light and converging emitted light, and zooming from a low magnification end state to a high magnification end state or from a high magnification end state to a low magnification end state. The second lens group, the third lens group, and the fourth lens group.
An afocal zoom lens characterized in that the lens group moves along the optical axis. 2. The afocal zoom lens according to claim 1, wherein the afocal zoom lens satisfies the following expression (1). | Fm1 / fm2 | <1.8 (1) where fm1 and fm2 are the focal lengths of the second, third, and fourth lens groups having negative refractive power, respectively, and | fm1 | ≧ | Each is selected so that fm2 |. 3. The afocal zoom lens according to claim 1 or 2, wherein the afocal zoom lens further satisfies the following expression (2). 1.5 <| fp / fm2 | <3.5 (2) Here, fp represents the focal length of the lens group having a positive refractive power among the second, third, and fourth lens groups. 4. Any one of claims 1 to 3
The afocal zoom lens according to the item 1, wherein the entrance pupil position is fixed 35 mm or more in front of the apex of the first lens. 5. Any one of claims 1 to 4
An optical device comprising the afocal zoom lens described in the item 1) in its optical system.