JP2001147378A - Objective lens system for parallel stereo microscope - Google Patents

Abstract

(57) [Problem] To provide an objective lens system for a parallel stereo microscope in which distortion is suppressed to a practically negligible level, image flatness is secured, and chromatic aberration is corrected to the utmost. SOLUTION: The objective lens system for a parallel stereo microscope according to the present invention includes a first lens group G1 having a positive refractive power and a second lens including at least one cemented triplet in order from a side farther from an object. It has a group G2 and a third lens group G3 having a positive refractive index.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an objective lens system for a stereomicroscope, and more particularly to an objective lens system suitable for a parallel single objective lens type binocular stereomicroscope.

[0002]

2. Description of the Related Art A stereomicroscope can observe a three-dimensional object when observing an object having irregularities in the same manner as when viewed with both eyes. Therefore, when working under a microscope, the distance relationship between a tool such as tweezers and an object can be easily grasped. Therefore, the present invention is particularly effective in fields requiring fine treatment, such as the precision machine industry, dissection of living organisms, and surgery. In a stereo microscope, in order to obtain parallax for a three-dimensional effect of an object, the optical systems of the light beams incident on the two right and left eyes are at least partially made independent so that their optical axes intersect on the object plane.
Then, a magnified image of the object viewed from a different direction is created, and the minute object is stereoscopically viewed by observing through an eyepiece. A representative method for obtaining a stereoscopic view of a stereomicroscope is a parallel stereomicroscope. The parallel stereo microscope has one objective lens system and two observation optical systems for the right eye and the left eye arranged parallel to the optical axis of the objective lens system.

[0003]

In the parallel stereo microscope, the difference between the right and left viewing optics is that the luminous flux passing through the objective lens system is decentered between the right-eye viewing optical system and the left-eye viewing optical system. It is a factor that causes it. Here, when the right-eye observation optical system and the left-eye observation optical system have different amounts of distortion respectively, or when the absolute amount of distortion that each optical system has is very large, etc. Observed images are generated by the left and right optical systems. When these images are fused, that is, fused, by an observer, they appear as distortions such as a feeling of convexity because the depth perception of the object is disturbed.

[0004] For example, as an example where the effect is most remarkable,
When observing a flat sample, there is a phenomenon in which an observation image is not flat but looks convex and protrudes, giving a sense of incongruity to the observer. Also, near the center of the image,
If the rate of change of the amount of distortion from the periphery is large, distortion of the image is emphasized, which is one of the causes of deteriorating the flatness of the image. As an optical system that reduces unnecessary three-dimensional effect of an observed image due to such distortion, for example, the optical systems disclosed in Japanese Patent Publication No. 7-60218 and Japanese Patent Application Laid-Open No. 10-26729 are known. Have been.

[0005] For this reason, in a stereomicroscope, it is desirable that the absolute amount of distortion is small, and furthermore, only the absolute amount such as the difference in distortion between the left and right observation optical systems and the difference in distortion due to image height is required. Instead, it is preferable to consider the qualitative aberration amount. Needless to say, it is necessary to correct not only distortion but also other aberrations (spherical aberration, astigmatism, curvature of field, coma) in a well-balanced manner in consideration of the above problems. . Further, in the case of a stereomicroscope, since a system having a zoom optical system is generally used, it is necessary to correct aberrations corresponding to a change in a field of view due to zooming or a change in numerical aperture.

However, with the recent increase in zoom ratio,
Removal of lateral chromatic aberration at low magnification, axial chromatic aberration at high magnification,
In particular, it has become very difficult to remove the remaining secondary spectrum.

In the case of a parallel-type single objective lens type stereomicroscope, the luminous flux from the center of the sample is limited by the effective diameter of the zoom optical system for the right eye and the zoom optical system for the left eye. For this reason, since the objective lens system is not used over the entire effective diameter, it can be said that, in principle, it is not necessary to correct aberrations over the entire effective diameter of the objective lens system. However, the optical system of the parallel stereo microscope is an eccentric optical system in which the optical axis of the objective lens system and the optical axis of the observation optical system for the right eye (or for the left eye) are eccentric. However, it is inevitable that asymmetrical aberrations such as chromatic aberration of magnification and chromatic coma occur. In order to suppress these aberrations, it is desirable that the objective lens system sufficiently corrects the chromatic spherical aberration over the secondary spectrum and its entire effective diameter. For this reason, an extremely bright objective lens system is required which has an aperture angle of substantially the angle θ (see FIG. 1) between the light beam passing through the outermost edge of the zoom optical system and the optical axis of the objective lens.

In the above-described optical system disclosed in Japanese Patent Publication No. 7-60218 and Japanese Patent Application Laid-Open No. 10-26729, the spherical aberration of a light beam having a shorter wavelength than the reference wavelength is overcorrected in the peripheral region. This is a practical problem. In particular, when the zoom optical system is used in combination with a zoom optical system having a high zoom ratio, a large problem occurs at a high magnification.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has an apochromat-class single objective in which distortion is suppressed to a practically acceptable level, the flatness of the image surface is ensured, and chromatic aberration is corrected to the utmost. It is an object of the present invention to provide an objective lens system suitable for a lens-type binocular parallel stereo microscope.

[0010]

In order to solve the above-mentioned problems, the present invention provides, in order from the side farthest from an object, a first lens group having a positive refractive power and at least one three-element cemented lens. An objective lens system for a parallel stereo microscope, comprising: two lens groups; and a third lens group having a positive refractive index. Here, the side far from the object is
The side where the observer of the stereomicroscope exists.

As described above, a planar sample (object)
However, the phenomenon observed in a convex shape by a stereoscopic microscope is because the way of distortion of the image seen by the left eye and the way of distortion of the image seen by the right eye are different, and the amount of difference is used as parallax. An illusion, resulting in a sense of depth that does not actually exist. The main cause is due to the distortion of the principal ray passing through the observation optical system for the right eye and the observation optical system for the left eye. Therefore, in order to solve the problem of the sense of depth, the absolute amount of distortion may be reduced.

However, the objective lens system of a stereomicroscope differs from a general microscope objective lens system in that the center position of the pupil is located outside the center position of the objective lens system, that is, the center of the pupil and the objective lens system. Since the positions do not match, it is difficult to perform power correction centering on the pupil. Such a correction is very difficult, especially with a high-magnification objective lens system having a short focal length. Therefore, it is important to reduce the difference between the distortion of the observation optical system for the left eye and the distortion of the observation optical system for the right eye.

[0013] Among the light beams from the object arranged about the optical axis, the light beam from one end (outermost peripheral portion) of the object passes through the peripheral portion of the objective lens system and is greatly bent. Since the light beam from the other end of the object passes near the center of the objective lens system, the light beam travels relatively straight without being bent. For this reason, the light beam passing through the end (peripheral portion) of the objective lens system is more affected by the aberration, and the negative distortion is increased. In the objective lens system of the parallel stereo microscope, it is desirable that the objective lens system has a lens configuration that minimizes the unbalance of the influence of the aberration due to the different optical paths. In the following, a description will be given assuming that a ray travels in a direction of reverse tracking from a side far from the object to the object side, in principle, including an embodiment described later.

The principal ray of the afocal light beam (parallel light beam) emitted from the pupil plane enters the objective lens system at a large angle on the low zoom side. For this reason, the positive (convex) refractive power of the first lens group suppresses the angle to a position close to being parallel to the optical axis. Also, in order to cancel the negative distortion, a relatively strong negative refractive power is required, but if this negative refractive power is provided near the object side, the principal point position is closer to the pupil plane side, The working distance is shortened. Therefore, it is desirable to dispose this negative refractive power on the pupil plane side as much as possible. However, if this negative refractive power is arranged in the first lens group closest to the pupil plane, the height of the light passing through the objective lens system from the optical axis becomes too high as described above, and other aberrations are corrected. It becomes difficult to do. Therefore,
It is desirable to dispose a negative refractive power (concave surface) immediately after the positive (convex) refractive power of the first lens group. Due to such a refractive power arrangement, the light beam passing through the peripheral portion of the objective lens system is first
The light is bent by the lens group, and when the light enters the concave surface of the subsequent second lens group, the angle of incidence increases, thereby contributing to the generation of a larger positive distortion on the surface. On the other hand, the principal ray of the other light beam passing near the optical axis of the objective lens system is not significantly affected by the aberration, so that the difference in distortion between the left-eye observation optical system and the right-eye observation optical system is small. Is shrinking.

The second lens group has a role of correcting chromatic aberration at the same time as correcting the above-described distortion. The concave surface provided to correct the distortion has the effect of jumping up the optical path of the principal ray passing through the periphery of the objective lens system at low zoom magnification, and also has a relatively large aperture luminous flux at high zoom magnification. Spread it. If this concave surface has a large achromatizing effect, spherical aberrations at long wavelengths with respect to the reference wavelength will be undercorrected, and spherical aberrations at short wavelengths will be overcorrected. Cause. Therefore, it is desirable to avoid using a glass material having a large dispersion difference in a portion where the rate of change in the height of the aperture light beam is large.

Therefore, it is desirable that the chromatic aberration be substantially corrected after the aperture light beam expanded by the concave surface of the second lens group approaches a parallel light beam with a positive refractive power. As described above, if the position where the color correction is performed is limited in the optical system, it is inevitable to use a glass material having a large dispersion for the concave lens, but these glass materials are generally positive (convex).
The difference in partial dispersion ratio with the lens is large. This is disadvantageous for correcting the secondary spectrum. Conversely, when a glass material having a relatively small dispersion, which is advantageous for the correction of the secondary spectrum, is used, the radius of curvature of the joint surface becomes tight (small). Cause. In other words, in the portion where the image height is high, the difference between the distortion of the observation optical system for the right eye and the distortion of the observation optical system for the left eye is small,
The phenomenon that the difference is large in the vicinity of the center where the image height is low, or conversely, the difference of the distortion in the portion where the image height is high becomes large,
In the vicinity of the center where the image height is low, a phenomenon occurs in which the difference becomes small. The difference in the amount of distortion is a factor that gives an unnecessary convex feeling to the observed image when observing a planar object. In the present invention,
The above-mentioned problem is solved by providing the triplet lens in the second lens group.

In the present invention, it is desirable that the second lens group includes a cemented lens including a cemented surface having a concave surface facing the object side. More preferably, the three cemented lens preferably includes the cemented surface with the concave surface facing the object side.

In the present invention, when the radius of curvature of the joint surface is R and the focal length of the objective lens system for a parallel stereomicroscope is F, (1) 0.3 <| R / F | <0 .9 should be satisfied.

Conditional expression (1) defines an appropriate range of the radius of curvature of the cemented surface with respect to chromatic aberration correction. When the value exceeds the upper limit of conditional expression (1), the radius of curvature of the joint surface becomes too loose, and the axial chromatic aberration and the lateral chromatic aberration are insufficiently corrected. Conversely, when the value goes below the lower limit of conditional expression (1), the radius of curvature becomes too tight, causing a difference in distortion between the observation optical system for the right eye and the observation optical system for the left eye when the zoom is low.

In the present invention, the focal length of the first lens group is F1, the focal length of the third lens group is F3, the Abbe number of the third lens group is νd3, and the objective lens for the parallel stereo microscope. Assuming that the focal length of the system is F, the following condition is satisfied: (2) 1.2 <F1 / F <7.5 (3) 1.0 <F3 / F <3.0 (4) νd3> 70 It is desirable.

Here, when the third lens group is composed of a plurality of single lens components, the average value of Abbe numbers of the plurality of single lens components is νd3.

Conditional expression (2) defines an appropriate range of the focal length of the first lens group. When the value exceeds the upper limit of conditional expression (2), the refractive power of the first lens unit becomes weak, so that the height of the light beam cannot be suppressed and it becomes difficult to correct various aberrations including spherical aberration. Conversely, when the value goes below the lower limit of conditional expression (2), a sufficient working distance cannot be obtained because the principal point position depends on the pupil side.

The conditional expression (3) defines an appropriate range of the focal length of the third lens unit. If the upper limit of conditional expression (3) is exceeded, the refractive power of the second lens group must be increased as a result, and the aberration balance of chromatic aberration will be lost. Conversely, if the lower limit of conditional expression (3) is not reached, the working distance becomes short, and it becomes difficult to correct astigmatism when zooming at low magnification.

The conditional expression (4) defines an appropriate range of the Abbe number of the glass material used for the third lens unit. If the lower limit of conditional expression (4) is not reached, lateral chromatic aberration at low zoom power and spherical aberration of color at high zoom power cannot be corrected.

[0025]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a diagram showing a schematic configuration of an optical system of a parallel stereo microscope provided with an objective lens system _LOB for a parallel stereo microscope according to the present invention. One objective lens system L
_OB is located at a focal distance F from the object O.
Then, the optical axis AX _OB parallel observation optical system for observation optical system L _R and the left eye right eye to L _L of the objective lens system L _OB is provided independently. The observation optical system L _R for the right eye, in order from the object O side, magnifies the afocal zoom lens system L _ZR , the imaging lens system L _IR that forms an intermediate image I _R ′ of the object, and the intermediate image and a an eyepiece lens system L _ER to. Then, the final image is observed with the naked eye (not shown) at a predetermined eye point position. The left-eye observation optical system _LL has the same configuration. Each optical axis AX _R of the right-eye observation optical system L _R and the left-eye observation optical system L _L, AX _L is the objective lens system L _OB optical axis A
It is inclined by a predetermined angle θ in the object plane with respect to X _OB. With this parallax, the object O can be three-dimensionally observed.

(First Embodiment) FIG. 2 is a diagram showing a lens configuration of an objective lens system for a stereomicroscope according to a first embodiment. A first lens group G1 composed of a cemented convex lens in which a convex lens L1 and a concave lens L2 are cemented in order from a surface (pupil surface) far from the object, and a lens L3 and a lens L4 each having the concave surface facing the surface (pupil surface) far from the object. A concave meniscus lens, a concave lens L5, a convex lens L6, and a concave lens L7.
The second lens group G2 includes a cemented lens and the third lens group G3 includes a single convex lens L8.

Although the meniscus lenses of the second lens group G2 are cemented, there is almost no difference in the dispersion of the respective glasses, so that they do not contribute much to achromatism (correction of chromatic aberration). Therefore, most of the correction of the axial chromatic aberration and the lateral chromatic aberration is performed by the following three cemented lenses L5, L6, and L7.

Here, since a glass having a large dispersion such as a heavy flint type is not used in order not to deteriorate the secondary spectrum, the achromatizing ability is insufficient with two cemented lenses. For this reason, if chromatic aberration is corrected by making the radius of curvature of the bonding surface tight, other aberrations such as distortion and astigmatism cannot be corrected. Therefore, in the present invention, a three-element cemented lens is employed, and the refractive power of the concave lens is divided into two elements, whereby the radius of curvature of the cemented surface can be reduced, and the deterioration of the secondary spectrum can be reduced. I have. Since the second lens group G2 has a small refractive power as a whole, the third lens group G2 includes a single lens L8 that is convex thereafter.
A lens group G3 is provided to guide the light beam to the object plane O.

Table 1 shows values of the objective lens system for a stereomicroscope according to the present embodiment. In the table, the number at the left end is the order of the lens surfaces counted from the surface (pupil surface) far from the object,
r is the radius of curvature of each lens surface, d is the surface spacing, nd and νd
Is the d line (λ = 587.56) of the glass material used for each lens.
The refractive index and Abbe number relative to nm) and F represent the focal length of the objective lens system for a stereomicroscope, respectively. Also,
Units such as a radius of curvature, a surface interval, and a focal length are mm.
Note that the same reference numerals as in the present embodiment are used in the specification values of all the embodiments below.

[0031]

[Table 1] (Values corresponding to conditional expressions) (1) | R / F | = 0.443 (2) F1 / F = 1.762 (3) F3 / F = 1.720 (4) νd3 = 82.52 FIG. FIG. 4 is a diagram illustrating various aberrations of the objective lens system for a parallel stereo microscope according to the present embodiment. In each aberration diagram, y indicates an image height, in the astigmatism diagram, S indicates a sagittal surface, and M indicates a meridional surface. In addition, the lateral aberration corresponds to that at the time of high magnification of the zoom, and the astigmatism and the distortion aberration correspond to those at the time of low magnification of the zoom. In the various aberration diagrams of all the embodiments below, the same reference numerals are used as in the aberration diagrams of the present embodiment. As is clear from the aberration diagrams, various aberrations are favorably corrected in the present embodiment.

(Second Embodiment) FIG. 4 is a view showing a lens configuration of an objective lens system for a parallel stereo microscope according to a second embodiment. The basic lens configuration is the same as that of the first embodiment, and the description is omitted. Table 2 below shows the specification values of the present embodiment.

[0033]

[Table 2] (Values corresponding to conditional expressions) (1) | R / F | = 0.459 (2) F1 / F = 1.825 (3) F3 / F = 2.683 (4) νd3 = 82.52 FIG. FIG. 4 is a diagram illustrating various aberrations of the objective lens system for a parallel stereo microscope according to the present embodiment. As is clear from the aberration diagrams, various aberrations are favorably corrected in the present embodiment.

(Third Embodiment) FIG. 6 is a diagram showing a lens configuration of an objective lens system for a parallel stereo microscope according to a third embodiment. A first lens group G1 composed of a convex single lens L1 and a negative meniscus single lens L having a concave surface facing the surface (pupil surface) far from the object in order from the surface (pupil surface) far from the object.
A second lens group G2 including two or two convex single lenses L3 and L4, a three-element cemented lens of a concave lens L5, a convex lens L6 and a concave lens L7, and a third lens group including a convex single lens L8.
It is constituted by a lens group G3.

Since the focal length is shorter than those of the first and second embodiments, a convex lens is added to the second lens group G2, but the structures of various aberrations are almost the same as those of the above embodiments. .

Table 3 shows the specification values of this embodiment.

[0037]

[Table 3] (Values corresponding to conditional expressions) (1) | R / F | = 0.671 (2) F1 / F = 3.462 (3) F3 / F = 1.501 (4) νd3 = 71.31 FIG. FIG. 4 is a diagram illustrating various aberrations of the objective lens system for a parallel stereo microscope according to the present embodiment. As is clear from the aberration diagrams, various aberrations are favorably corrected in the present embodiment.

(Fourth Embodiment) FIG. 8 is a diagram showing a lens configuration of an objective lens system for a parallel stereo microscope according to a fourth embodiment. A first lens group G1 composed of a cemented convex lens in which a concave lens L1 and a convex lens L2 are cemented in order from a surface (pupil surface) far from the object, a concave lens L3 with a concave surface facing the surface (pupil surface) far from the object, and a convex lens L4 , Convex lens L5, three cemented meniscus lens, concave lens L6 and convex lens L
7, a second lens group G2 consisting of a cemented lens
The third lens group G3 is composed of a single lens L8 and L9.

This embodiment is slightly different from the first to third embodiments in the aberration structure, and employs a triple cemented lens as the meniscus lens of the second lens group G2. Concave lens L
A convex lens L4 having a relatively large dispersion is interposed between the convex lens L5 and the convex lens L5 to prevent the spherical aberration on the short wavelength side from being overcorrected. The spectrum is kept good.

Table 4 shows the specification values of this embodiment.

[0041]

[Table 4] (Values corresponding to conditional expressions) (1) | R / F | = 0.804 (2) F1 / F = 7.004 (3) F3 / F = 1.419 (4) νd3 = 73.97 FIG. FIG. 4 is a diagram illustrating various aberrations of the objective lens system for a parallel stereo microscope according to the present embodiment. As is clear from the aberration diagrams, various aberrations are favorably corrected in the present embodiment.

[0042]

As described above, according to the present invention,
The objective lens system for a parallel stereomicroscope, which suppresses distortion to the extent that there is no practical problem, secures the flatness of the image, and corrects the chromatic aberration to the utmost, especially the apochromat class parallel single objective lens type binocular An objective lens system suitable for a stereomicroscope can be provided.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a configuration of a parallel single objective lens type objective lens system for a binocular stereomicroscope.

FIG. 2 is a diagram showing a lens configuration of an objective lens system for a parallel stereo microscope according to a first example.

FIG. 3 is a diagram illustrating various aberrations of the objective lens system for a parallel stereo microscope according to the first example.

FIG. 4 is a diagram showing a lens configuration of an objective lens system for a parallel stereo microscope according to a second embodiment.

FIG. 5 is a diagram showing various aberrations of the objective lens system for a parallel stereo microscope according to the second example.

FIG. 6 is a diagram showing a lens configuration of an objective lens system for a parallel stereo microscope according to a third embodiment.

FIG. 7 is a diagram illustrating various aberrations of the objective lens system for a parallel stereo microscope according to the third example.

FIG. 8 is a diagram showing a lens configuration of an objective lens system for a parallel stereo microscope according to a fourth embodiment.

FIG. 9 is a diagram illustrating various aberrations of the objective lens system for a parallel stereo microscope according to the fourth example.

[Explanation of symbols]

O Object L1 to L9 Each lens component G1 First lens group G2 Second lens group G3 Third lens group L _OB objective lens system L _R Observation optical system for right eye L _L Observation optical system for left eye L _ZR , L _ZL zoom variable power lens system L _IR, L _IL imaging lens system AX _OB objective lens system in the optical axis AX _L left-eye observation optical system in the optical axis AX _R right-eye observation optical system in the optical axis

Claims (4)

[Claims] 1. A first lens group having a positive refractive power, a second lens group including at least one triplet lens, and a third lens group having a positive refractive index in order from a side farther from the object. And an objective lens system for a parallel stereo microscope. 2. The objective lens system for a parallel stereo microscope according to claim 1, wherein the second lens group includes a cemented lens including a cemented surface having a concave surface facing the object side. 3. When the radius of curvature of the joining surface is R and the focal length of the objective lens system for a parallel stereo microscope is F, respectively: (1) 0.3 <| R / F | <0.9 3. The objective lens system for a parallel stereo microscope according to claim 1, wherein the objective lens system satisfies a condition. 4. The focal length of the first lens group is F1, the focal length of the third lens group is F3, the Abbe number of the third lens group is νd3, and the focal length of the objective lens system for the parallel stereo microscope. Is defined as F, the following condition is satisfied: (2) 1.2 <F1 / F <7.5 (3) 1.0 <F3 / F <3.0 (4) νd3> 70 The objective lens system for a parallel stereo microscope according to any one of claims 1 to 3.