JP2011221409A - Objective lens system for parallel system stereomicroscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an objective lens system for a parallel system stereomicroscope, the lens system which allows realization of excellent focusing performance by suppressing distortion aberration to a degree practically free of problem to secure flatness on an image plane and by appropriately correcting other various aberrations.SOLUTION: The objective lens system for a parallel system stereomicroscope Lcomprises: a first lens group G1 including a cemented lens B1 of which the component lenses are lined up in order from the farthest side from an object Ob and which has a negative refractive power, the lens group G1 as a whole having a positive refractive power; a second lens group G2 including a lens having a meniscus shape with the convex surface facing the object side and a negative refractive power, and a cemented lens having a positive refractive power; and a third lens group G3 including at least a single lens having a positive refractive power, and having a positive refractive power as a whole. Where "fB1" is the focal distance of the cemented lens B1 constituting the first lens group G1 and having a negative refraction power and "f" is the focal distance of the objective lens system Las a whole, the condition represented by the formula 1.00<(-fB1)/f<20.00 is satisfied.

Description

  The present invention relates to an objective lens system for a parallel stereomicroscope.

  With a stereomicroscope, when an uneven object is observed, it can be observed with a three-dimensional effect in the same way as when viewed with both eyes. For this reason, when working under a microscope, it is possible to easily grasp the distance relationship between a tool such as tweezers and an object. Therefore, it is particularly effective in fields requiring fine treatment such as precision machine industry, biological dissection, and surgery. In a stereomicroscope, in order to obtain a parallax for a three-dimensional effect of an object, the optical systems of light beams incident on the left and right eyes are at least partially independent so that their optical axes intersect on the object plane. Then, a magnified image of the object viewed from different directions is created and observed through an eyepiece to stereoscopically view the minute object. As a typical method for obtaining a stereoscopic view of a stereomicroscope, a parallel stereomicroscope can be cited. The parallel system stereomicroscope has one objective lens system and two observation optical systems for the right eye and for the left eye arranged in parallel to the optical axis of the objective lens system. As such an objective lens system for a parallel stereomicroscope, for example, those described in Patent Documents 1 and 2 below are disclosed.

JP 2001-147378 A JP 2001-221955 A

  In the parallel system stereomicroscope, the fact that the light beam passing through the objective lens system is decentered between the observation optical system for the right eye and the observation optical system for the left eye is a factor causing a difference in the left and right appearance. For this reason, when the right-eye observation optical system and the left-eye observation optical system have different amounts of distortion, or when the absolute amount of distortion aberration of each optical system itself is large, the distortion is asymmetrically distorted. A unique observation image is generated in the left and right observation optical systems. When these images are fused, that is, fused by the observer, the depth perception of the object is distorted and appears as distortion such as convexity. For example, as an example in which the influence is most prominent, there is a phenomenon in which when a flat specimen is observed, the observation image appears to be convex rather than flat, giving the viewer a sense of incongruity. In addition, if the rate of change in the amount of distortion between the vicinity of the center of the image and the periphery is large, the distortion of the image is emphasized, which is one of the causes of deterioration of the flatness of the image.

  For this reason, it is desirable that the stereo microscope has a smaller absolute amount of distortion. In addition to 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, It is preferable to consider qualitative aberrations. Needless to say, other aberrations (spherical aberration, astigmatism, curvature of field, etc.) need to be corrected in a well-balanced manner in consideration of the above-described problems as well as distortion. Furthermore, in the case of a stereomicroscope, since it is common to use a variable magnification optical system, aberration correction corresponding to a change in the visual field region or a change in the numerical aperture due to the variable magnification is required.

  The present invention has been made in view of such a problem, and even if the zooming range is expanded, distortion is suppressed to a level that does not cause a problem in practice, and the flatness of the image surface is ensured. An object of the present invention is to provide an objective lens system for a parallel stereo microscope capable of avoiding an increase in size and correcting other various aberrations and realizing an excellent imaging performance.

  In order to achieve such an object, the present invention includes a cemented lens having negative refractive power arranged in order from the side far from the object (that is, the observation optical system side), and has a positive refractive power as a whole. At least one lens group, including a lens group, a meniscus lens having a negative refractive power with a convex surface facing the object side, and a cemented lens having a positive refractive power, and a second lens group having a weak refractive power An objective lens system for a parallel stereomicroscope including a third lens group having a positive refractive power as a whole and including a single lens having a positive refractive power, and constituting the first lens group When the focal length of the cemented lens having a negative refractive power is fB1 and the focal length of the entire objective lens system is f, the following condition of 1.00 <(− fB1) / f <20.00 is satisfied. To do.

  In the present invention, the first lens group has a single lens having a positive refractive power, and when the Abbe number of the single lens having the positive refractive power constituting the first lens group is νdL1, It is preferable that the condition of the following formula νdL1 <40.0 is satisfied.

  In the present invention, the meniscus lens having a negative refractive power that forms the second lens group and has a convex surface facing the object side is a cemented meniscus lens in which a negative lens and a positive lens are bonded together. The cemented lens having a positive refractive power is preferably a cemented lens in which three lenses of a biconvex lens, a biconcave lens, and a biconvex lens are bonded together.

  Further, in the present invention, the objective lens system converts the light from the object into a parallel light beam, and guides the light beam to the subsequent two observation optical systems for the left eye and the right eye, thereby enabling stereoscopic viewing. The observation optical system includes a variable magnification optical system, the distance between the objective side axes at the maximum zoom magnification of the variable magnification optical system is SBH, and the minimum zoom magnification of the variable magnification optical system is When the distance between the objective-side axes of the objective lens system satisfies S 1 ≦ SBH−SBL ≦ 10, the maximum exit pupil diameter on the left and right sides of the objective lens system is φAP, and the objective lens system When the maximum object height that can be observed is Ymax, it is preferable to satisfy the following conditions: 23 ≦ φAP ≦ 30 and 0.160 ≦ Ymax / f.

  The present invention also provides a parallel stereomicroscope capable of stereoscopic viewing by converting light from an object into a parallel light beam and then guiding the light beam to two subsequent observation optical systems for the left and right eyes. Objective lens system, wherein the observation optical system includes a variable magnification optical system, the distance between the objective side axes at the maximum zoom magnification of the variable magnification optical system is SBH, and the minimum zoom magnification of the variable magnification optical system is When the distance between the objective-side axes at SBL is SBL, if the following condition is satisfied: 1 ≦ SBH−SBL ≦ 10, the maximum exit pupil diameter on the left and right sides of the objective lens system is φAP, and the objective lens system Where Ymax is the maximum observable object height, the following conditions are satisfied: 23 ≦ φAP ≦ 30 and 0.160 ≦ Ymax / f.

  In the present invention, the second lens group includes a contact multilayer diffractive optical element having a diffractive optical surface in which two diffractive element elements made of different optical materials are bonded and a diffraction grating groove is formed on the bonded surface. Of the two diffractive element elements made of different optical materials, the refractive indices of the optical material of the diffractive optical element having the lower refractive index and higher dispersion with respect to the d-line, F-line, and C-line are nd1, nF1, and nC1, respectively. The refractive indexes of the optical material of the diffractive optical element having the higher refractive index and lower dispersion with respect to the d-line, F-line, and C-line are nd2, nF2, and nC2, respectively, and the effective diameter of the diffractive optical surface of the diffractive optical element is When φLD is set and the maximum exit pupil diameter on the left and right sides of the objective lens system is φAP, the following equations nd1 ≦ 1.54, 0.0145 ≦ nF1-nC1, 1.55 ≦ nd2, nF2-nC2 ≦ It is preferable to satisfy the condition of .013 and 2.2 ≦ φLD / φAP.

  According to the present invention, it is possible to realize excellent imaging performance by suppressing distortion aberration to a practically no problem level, ensuring flatness of the image surface, and correcting other various aberrations well. An object lens system for a parallel stereo microscope can be provided.

1 is a schematic configuration diagram of a parallel single objective lens type objective lens system for a binocular stereomicroscope. FIG. It is a lens block diagram of the objective-lens system for parallel system stereomicroscopes concerning 1st Example. FIG. 6 is a lateral aberration diagram, an astigmatism diagram, and a distortion diagram of the objective lens system for the parallel stereomicroscope according to the first example. It is a lens block diagram of the objective-lens system for parallel system stereomicroscopes concerning 2nd Example. FIG. 6 is a lateral aberration diagram, an astigmatism diagram, and a distortion diagram of the objective lens system for the parallel stereomicroscope according to the second example. It is a lens block diagram of the objective-lens system for parallel system stereomicroscopes concerning 3rd Example. FIG. 10 is a lateral aberration diagram, an astigmatism diagram, and a distortion diagram of the objective lens system for the parallel stereomicroscope according to the third example. FIG. 2 is a schematic configuration diagram when the objective lens system according to the present embodiment is a decentered variable magnification optical system.

Hereinafter, the present embodiment will be described with reference to the drawings. First, a parallel stereo microscope (parallel single objective binocular microscope) including the objective lens system according to the present embodiment will be described. Parallel system stereomicroscope according to the present embodiment, as shown in FIG. 1, and one objective lens system L _ob disposed from the object Ob to the position of the focal length f, of the objective lens system L _ob optical axis AX _ob and an observation optical system L _L for parallel arranged right-eye observation optical system L _R and the left eye in. The right-eye observation optical system _LR includes an afocal zoom optical system L _ZR arranged in order from the object Ob side, an imaging optical system L _IR that forms an intermediate image of the object, and an intermediate and an eyepiece optical system L _ER to expand the image. The left-eye observation optical system _LL has the same configuration. The light from the object Ob is converted into a parallel light beam by the objective lens system L _ob , and an intermediate image is formed by the imaging optical systems L _IR and L _IL via the variable magnification optical systems L _ZR and L _ZL . The intermediate image is enlarged by the eyepiece optical systems L _ER and L _EL , and the final image is observed with the naked eye (not shown) at a predetermined eye point position. The parallel system stereomicroscope having such a configuration, AX _L of the optical axis AX _R and the left-eye observation optical system L _L of the right-eye observation optical system L _R is the optical axis AX _ob of the objective lens system L _ob respectively In contrast, the object surface is inclined by a predetermined angle θ. With this parallax, the object Ob can be observed stereoscopically.

In the present embodiment, the objective lens system L _ob has negative refractive powers arranged in order from the side far from the object Ob (that is, the observation optical system L _R , L _L side in FIG. 1), as shown in FIG. A first lens group G1 having a positive refractive power as a whole and a meniscus-shaped lens having a negative refractive power with the convex surface facing the object side (in FIG. 2, a cemented lens comprising lenses L21 and L22). A second lens group G2 having a weak refractive power, and a cemented lens having a positive refractive power (corresponding to a three-lens cemented lens including lenses L23, L24, and L25 in FIG. 2), and at least It includes a single lens having a positive refractive power (lens L31 and L32 in FIG. 2 respectively) and a third lens group G3 having a positive refractive power as a whole. With this configuration, it is possible to efficiently correct lateral chromatic aberration, distortion aberration, and image plane aberration at the time of zoom low magnification.

Then, based on the above configuration, the focal length of the cemented lens B1 having negative refractive power constituting the first lens group G1 is fB1, the focal length of the entire objective lens system L _ob is f, and the following conditional expression Satisfy (1).

      1.00 <(− fB1) / f <20.00 (1)

  The conditional expression (1) defines an appropriate range of the focal length of the cemented lens B1 having a negative refractive power and constituting the first lens group G1. When the upper limit of conditional expression (1) is exceeded, the negative refractive power of the cemented lens B1 becomes weak, and it becomes difficult to correct curvature of field and distortion at zoom low magnification. On the other hand, if the lower limit value of conditional expression (1) is not reached, the height of the light beam becomes too large, and it becomes particularly difficult to correct spherical aberration.

  In order to secure the effect of the present embodiment, it is preferable to set the lower limit of conditional expression (1) to 5.00. In order to secure the effect of the present embodiment, it is preferable to set the upper limit of conditional expression (1) to 9.00.

In the objective lens system L _ob of the present embodiment, when the focal length of the first lens group G1 is f1, and the focal length of the third lens group G3 is f3, the following conditional expressions (2) and (3) Is more preferable.
1.50 <f1 / f <5.00 (2)
1.00 <f3 / f <1.50 (3)

  Conditional expression (2) defines an appropriate range of the focal length of the first lens group G1. If the upper limit value of conditional expression (2) is exceeded, the positive refractive power of the first lens group G1 becomes weak, the height of the light beam becomes too large, and it becomes difficult to correct spherical aberration. On the contrary, if the lower limit value of conditional expression (2) is not reached, the principal point position becomes far from the object surface, and a sufficient working distance cannot be obtained.

  In order to secure the effect of the present embodiment, it is preferable to set the lower limit value of conditional expression (2) to 2.00. In order to secure the effect of the present embodiment, it is preferable to set the upper limit of conditional expression (2) to 3.50.

  Conditional expression (3) defines an appropriate range of the focal length of the third lens group G3. If the upper limit value of the conditional expression (3) is exceeded, the positive refractive power of the third lens group G3 becomes weak. As a result, the refractive power of the second lens group G2 is increased, and it is difficult to correct chromatic aberration. Become. On the other hand, if the lower limit of conditional expression (3) is not reached, the working distance is shortened, and correction of astigmatism and distortion at zoom low magnification becomes difficult.

  In order to secure the effect of the present embodiment, it is preferable to set the lower limit of conditional expression (3) to 1.10. In order to secure the effect of the present embodiment, it is preferable to set the upper limit of conditional expression (3) to 1.30.

In the objective lens system L _{ob according} to the present embodiment, the first lens group G1 has a single lens having a positive refractive power (the lens L11 corresponds to FIG. 2), and constitutes the first lens group G1. When the Abbe number of a single lens having positive refractive power is νdL1, it is preferable that the following conditional expression (4) is satisfied.

      νdL1 <40.0 (4)

  Conditional expression (4) defines an appropriate range of the Abbe number of a single lens glass material having a positive refractive power constituting the first lens group G1. If the upper limit value of the conditional expression (4) is exceeded, the color development effect in the first lens group G1 will be reduced, and the lateral chromatic aberration at zoom low magnification, and the spherical aberration and coma aberration of color at zoom high magnification will be corrected. It becomes difficult.

  In order to secure the effect of the present embodiment, it is preferable to set the upper limit of conditional expression (2) to 30.0.

In addition, the objective lens system L _{ob according} to the present embodiment includes a negative lens and a positive lens, which form the second lens group G2, and a meniscus lens having a negative refractive power facing the object side. A cemented meniscus lens (a cemented lens composed of lenses L21 and L22 in FIG. 2 is applicable), and the cemented lens having positive refractive power is composed of a biconvex lens, a biconcave lens, and a biconvex lens. It is preferably a cemented lens (in FIG. 2, a three-lens cemented lens composed of lenses L23, L24, and L25 is applicable). According to this configuration, since the achromatic cemented lens can be disposed at the maximum diameter in the present optical system, it is possible to efficiently correct spherical aberration and axial chromatic aberration at the time of zoom high magnification.

Further, the objective lens system L _{ob according} to the present embodiment converts the light from the object Ob into a parallel light beam, and then transmits the light beam to the subsequent two observation optical systems L _R and L _L for the left eye and the right eye. As shown in FIG. 8, the observation optical systems L _R and L _L are variable magnification optical systems L _ZR and L _ZL , and imaging optical systems L _IR , L _IL, ocular optical system L _ER, include L _EL, the variable magnification optical system L _ZR, the objective-side center distance between the zoom up times L _ZL and SBH, variable power optical system L _ZR, the zoom lowest L _ZL the objective-side axial distance at times a decentered variable magnification optical system according to SBL, when satisfying the following conditional expression (5), the maximum exit pupil diameter of the left and right side of the objective lens system L _ob and FaiAP, when the Ymax observable maximum object height of the objective lens system L _ob, preferably to satisfy the following conditional expression (6) and (7) Yes. In FIG. 8, when the distance between the objective-side optical axes of the observation optical systems L _R and L _L is SB, the state of SB = SBH and SBL <SB is shown. Here, the decentered variable magnification optical system is composed of a plurality of lens groups, and at least two lens groups of the plurality of lens groups are respectively provided in at least a part of a section where magnification is changed from the high magnification end to the low magnification end. A lens that moves so as to have a component in a direction orthogonal to the optical axis of the objective lens system.

1 ≦ SBH−SBL ≦ 10 (5)
23 ≦ φAP ≦ 30 (6)
0.160 ≦ Ymax / f (7)

Conditional expression (5) defines an appropriate amount of the difference in the distance between the objective-side optical axes of the left and right observation optical systems L _R and L _L when the zoom is at high magnification and at zoom low magnification. If the upper limit of this conditional expression (5) is exceeded, the distance between the objective-side optical axes of the left and right observation optical systems L _R and L _L becomes too narrow when zooming is low, and a sufficient stereo effect cannot be obtained or zooming is performed. At the time of high magnification, the distance between the objective-side optical axes of the left and right observation optical systems L _R and L _L becomes too large, and may not fit the eye width of the eyepiece optical systems L _ER and L _{EL at} the time of observation. On the other hand, if the lower limit value of conditional expression (5) is not reached, the objective lens system L _ob becomes large when the zoom is low.

  In order to secure the effect of the present embodiment, it is preferable to set the lower limit of conditional expression (5) to 4 or more. In order to secure the effect of the present embodiment, it is preferable to set the upper limit of conditional expression (5) to 8 or less.

Conditional expression (6) defines an appropriate size of the maximum exit pupil diameter on one of the left and right _sides of the objective lens system L _ob , in other words, the maximum entrance pupil diameter of the left and right observation optical systems L _R and L _L. If the upper limit of conditional expression (6) is exceeded, the distance between the objective optical axes of the left and right observation optical systems L _R and L _L becomes too large, and the eye width of the eyepiece optical systems L _ER and L _EL when observing Will not fit. On the other hand, if the lower limit value of conditional expression (6) is not reached, a sufficiently large NA cannot be obtained at zoom high magnification, and it becomes difficult to improve the resolution from the conventional product.

  In order to secure the effect of the present embodiment, it is preferable to set the lower limit of conditional expression (6) to 24 or more. In order to secure the effect of the present embodiment, it is preferable to set the upper limit of conditional expression (6) to 28 or less.

Conditional expression (7) defines an appropriate angle of view that enables observation with the objective lens system _Lob . If the lower limit of conditional expression (7) is not reached, it will be difficult to secure a sufficiently large real field of view that can be observed when the zoom is low.

  In order to secure the effect of the present embodiment, it is preferable to set the lower limit of conditional expression (7) to 0.200 or more.

In the objective lens system L _{ob according} to the present embodiment, as shown in FIG. 6, the second lens group G2 joins two diffractive element elements made of different optical materials, and a diffraction grating groove is formed on the joint surface. Among the two diffractive element elements made of different optical materials, the diffractive optical element having a low refractive index and high dispersion (shown in FIG. 6) has a multi-layered diffractive optical element LD having the formed diffractive optical surface D. Refractive indices of the optical material of the lens L24 with respect to the d-line, F-line, and C-line are nd1, nF1, and nC1, respectively, and the diffractive optical element having the higher refractive index and lower dispersion (corresponding to the lens L25 in FIG. 6). The refractive indices of the optical material for d-line, F-line, and C-line are nd2, nF2, and nC2, respectively, the effective diameter of the diffractive optical surface of the diffractive optical element LD is φLD, and the maximum emission on the left and right sides of the objective lens system L _ob When the pupil diameter is φAP, It is preferable that the following conditional expressions (8) to (12) are satisfied.

nd1 ≦ 1.54 (8)
0.0145 ≦ nF1-nC1 (9)
1.55 ≦ nd2 (10)
nF2-nC2 ≦ 0.013 (11)
2.2 ≦ φLD / φAP (12)

In the objective lens system L _{ob according} to the present embodiment, it is preferable that the second lens group G2 is provided with a diffractive optical element LD, particularly for correcting chromatic aberration. The diffractive optical element LD includes a diffractive optical surface D in which several to hundreds of fine groove-shaped or slit-shaped grating structures are formed concentrically per 1 mm, and light incident on the diffractive optical surface D is grating pitch. It has the property of diffracting in a direction determined by the (grating groove interval) and the wavelength of incident light. The diffractive optical element LD (diffractive optical surface D) has a negative dispersion value (Abbe number = −3.45 in the embodiment of the present application), large dispersion, and anomalous dispersion (partial dispersion in the embodiment of the present application). Since the ratio (ng-nF) / (nF-nC) = 0.296) is strong, it has a strong ability to correct chromatic aberration. The Abbe number of the optical glass is usually about 30 to 80, but the Abbe number of the diffractive optical element has a negative value. In other words, the diffractive optical surface D of the diffractive optical element GD has a dispersion characteristic that is opposite to that of normal glass (refractive optical element), and the refractive index decreases as the wavelength of light decreases. It has the property of bending. Therefore, a large achromatic effect can be obtained by combining with an ordinary refractive optical element. Therefore, chromatic aberration can be favorably corrected by using the diffractive optical element LD.

The diffractive optical element LD in the present embodiment joins two diffractive element elements (for example, optical members L24 and L25 in the case of FIG. 6) made of different optical materials, and provides a diffraction grating groove on the joint surface to provide diffractive optics. This is a so-called “contact multilayer diffractive optical element” constituting the surface D. Therefore, this diffractive optical element can increase the diffraction efficiency in a wide wavelength region including g-line to C-line. Therefore, the objective lens system L _ob according to the present embodiment can be used in a wide wavelength region. The diffraction efficiency indicates the ratio η (= I1 / I0 × 100 [%]) between the incident intensity I0 and the intensity I1 of the first-order diffracted light when the first-order diffracted light is used in the transmission type diffractive optical element.

In addition, the contact multilayer diffractive optical element LD is compared to a so-called separated multilayer diffractive optical element in which two diffraction element elements formed with diffraction grating grooves are arranged close to each other so that the diffraction grating grooves face each other. Thus, the manufacturing process can be simplified, so that the mass production efficiency is good and the diffraction efficiency with respect to the incident angle of the light beam is good. Therefore, the microscope objective lens L _{ob according} to the present embodiment using such a contact multilayer diffractive optical element LD is easy to manufacture and also improves the diffraction efficiency.

  Here, the conditional expressions (8) to (11) indicate that the refractive index of the material of the two different diffractive element elements constituting the diffractive optical element LD and the refractive index difference (nF−nC) with respect to the F-line and C-line. Respectively. By satisfying these conditional expressions (8) to (11), it is possible to form the diffractive optical surface D by closely bonding two different diffractive element elements with better performance. As a result, a diffraction efficiency of 90% or more can be realized over a wide wavelength range from g-line to C-line. However, if the upper limit value of conditional expressions (8) to (11) is exceeded or falls below the lower limit value, it becomes difficult to obtain a diffraction efficiency of 90% or more in a wide wavelength region, and the contact multilayer diffractive optical element LD. It will be difficult to maintain the benefits.

  The conditional expression (12) defines an appropriate size of the diameter of the diffractive optical surface D that forms the contact multilayer diffractive optical element LD. If the lower limit value of the conditional expression (12) is not reached, a sufficient achromatic effect by the diffractive optical surface D cannot be obtained, and it becomes difficult to achieve apochromat class performance.

  In order to secure the effect of the present embodiment, it is preferable to set the lower limit of conditional expression (12) to 2.4 or more.

  In the present embodiment, the diffractive optical element LD can be provided on a curved surface instead of being provided on the plane constituting the second lens group G2 as shown in FIG.

Furthermore, in the present embodiment, it is preferable that the following conditional expression (13) is satisfied, where f2 is the focal length of the second lens group G2 and f is the focal length of the entire objective lens system _Lob. .

      6.00 <| f2 / f | (13)

  Conditional expression (13) defines an appropriate range of the focal length of the second lens group G2. If the lower limit of conditional expression (13) is not reached, the refractive power of the second lens group G2 becomes too strong, making it difficult to satisfactorily correct spherical aberration and longitudinal chromatic aberration.

  In order to secure the effect of the present embodiment, it is preferable to set the lower limit value of conditional expression (13) to 8.00.

  Hereinafter, each example according to the present embodiment will be described with reference to the drawings. Tables 1 to 3 are shown below, but these are tables of specifications in the first to third examples.

  In the table, the surface number is the order of the lens surfaces counted from the side far from the object Ob, r is the radius of curvature of each lens surface, and d is the distance from each optical surface to the next optical surface (or object Ob). The interplanar spacing, which is the distance on the optical axis, nd is the refractive index for the d-line (wavelength 587.6 nm), and νd is the Abbe number for the d-line. The curvature radius “∞” indicates a plane. Also, the refractive index of air of 1.0000 is omitted.

  In the following examples, the phase difference of the diffractive optical surface D formed on the contact multilayer diffractive optical element LD is an ultrahigh refraction performed using a normal refractive index and an aspherical formula (a) described later. Calculated by the rate method. The ultrahigh refractive index method uses a certain equivalent relationship between the aspherical shape and the grating pitch of the diffractive optical surface. In this embodiment, the diffractive optical surface D is replaced by the ultrahigh refractive index method. As data, that is, an aspherical expression (a) described later and its coefficient. In this embodiment, d-line, C-line, F-line and g-line are selected as the calculation target of the aberration characteristics. The wavelengths of these d-line, C-line, F-line and g-line used in this example and the refractive index values used for calculation of the ultrahigh refractive index method set for each spectral line are shown in the following table. 4 shows.

(Table 4)
Wavelength Refractive index (by ultra high refractive index method)
d-line 587.562nm 10001.0000
C line 656.273nm 11170.4255
F line 486.133nm 8274.7311
g-line 435.835nm 7418.6853

In each embodiment, the height of the aspheric surface in the direction perpendicular to the optical axis is y, and the distance (sag amount) along the optical axis from the tangential plane of the apex of each aspheric surface to each aspheric surface at height y. Is S (y), r is the radius of curvature of the reference sphere (vertex radius of curvature), κ is the conic constant, and An is the nth-order aspherical coefficient. In the following examples, “E-n” represents “× 10 ⁻ⁿ ”.

S (y) = (y ² / r) / {1+ (1−κ × y ² / r ² ) ^1/2 }
+ A2 × y ² + A4 × y ⁴ + A6 × y ⁶ + A8 × y ⁸ (a)

  In each example, the lens surface on which the diffractive optical surface is formed is marked with an asterisk (*) on the right side of the surface number in the table. The aspherical expression (a) indicates the performance of the diffractive optical surface. The specifications are shown.

In the tables, f is the focal length of the entire system of the objective lens system L _ob, WD to the working distance, fB1 the focal length of the cemented lens having a negative refractive power constituting the first lens group G1, f1 is a focal length of the first lens group G1, f2 is a focal length of the second lens group G2, f3 is a focal length of the third lens group G3, and νdL1 is a positive constituting the first lens group G1. SBH is the maximum magnification of the left and right observation optical systems L _R and L _L used in combination with the objective lens system (more specifically, by the variable magnification optical systems L _ZR and L _ZL ). The SBL is the distance between the objective side axes at the minimum zoom of the left and right observation optical systems L _R and L _L (using the variable magnification optical systems L _ZR and L _ZL ) used in combination with the objective lens system. ΦAP is the maximum exit pupil diameter on the left and right sides of the objective lens system L _ob The, Ymax denotes the maximum object height observable objective lens system L _ob respectively. Further, the table also shows values corresponding to the conditional expressions (1) to (13).

  Hereinafter, “mm” is generally used for the focal length f, the radius of curvature r, the surface interval d, and other lengths, etc. unless otherwise specified, but the optical system is proportionally enlarged or proportional. Since the same optical performance can be obtained even if the image is reduced, the present invention is not limited to this. Further, the unit is not limited to “mm”, and other appropriate units can be used.

  The description of the table so far is common to all the embodiments, and the description below is omitted.

(First embodiment)
The objective lens system L _ob (L _ob1 ) for the parallel stereomicroscope according to the first example will be described with reference to FIGS. 2 and 3 and Table 1. FIG. As shown in FIG. 2, the objective lens system L _ob1 for the parallel stereomicroscope according to the first example is arranged in order from the side far from the object Ob, and has a first lens group G1 having a positive refractive power as a whole, It has a second lens group G2 having a relatively weak refractive power and a third lens group G3 having a positive refractive power as a whole.

  The first lens group G1 includes a biconvex lens L11, a negative meniscus lens L12 having a concave surface facing the object side, and a biconvex lens L13, which are arranged in order from the side far from the object Ob, and has a negative refractive power as a whole. And a lens.

  The second lens group G2 is composed of a negative meniscus lens L21 having a convex surface facing the object side and a positive meniscus lens L22 having a convex surface facing the object side, which are arranged in order from the side farther from the object Ob. A cemented lens having a negative meniscus refractive power with a convex surface and a biconvex lens L23, a biconcave lens L24, and a biconvex lens L25 are bonded together to form a cemented lens having a positive refractive power as a whole.

  The third lens group G3 includes a biconvex lens L31 and a biconvex lens L32 arranged in this order from the side farther from the object Ob.

  Table 1 lists the values of each item in the first embodiment. In addition, the surface numbers 1-16 of Table 1 respond | correspond to the surfaces 1-16 shown in FIG.

The distance between the objective optical axes of the observation optical systems L _R and L _L is SB = 26 mm (fixed), and the maximum effective diameter of the objective lens system L _ob1 is Dmax = 80 mm. In addition, the entrance pupil positions of the observation optical systems L _R and L _L are at a position 43 mm from the first surface of the objective lens system L _{ob1 at} a zoom minimum of 43 mm, a zoom maximum magnification of 242 mm, and a position away from the object plane Ob.

(Table 1)
f = 50.2
WD = 31.0
fB1 = -288.0
f1 = 147.9
f2 = 652.7
f3 = 61.5

Surface number r d nd
νd
1 116.46700 7.500 1.84666 23.9
2 -284.85506 0.500
3 142.07687 3.000 1.83481 42.7
4 35.04100 14.481 1.43425 95.0
5 -230.00729 9.576
6 -34.05100 3.745 1.74950 35.3
7 -139.48185 15.336 1.43425 95.0
8 -40.09000 0.500
9 154.98239 14.731 1.59240 68.3
10 -125.00000 4.000 1.90265 35.7
11 126.14143 20.000 1.59240 68.3
12 -90.02700 0.500
13 179.34654 13.031 1.59240 68.3
14 -178.07559 0.500
15 56.52200 16.000 1.59240 68.3
16 1102.18933

[Conditional expression]
Conditional expression (1) (-fB1) / f = 5.74
Conditional expression (2) f1 / f = 2.95
Conditional expression (3) f3 / f = 1.22
Conditional expression (4) νdL1 = 23.9
Conditional expression (13) | f2 / f | = 13.00

Of the values of the conditional expressions shown in Table 1, conditional expression (4) corresponds to the value of the first surface. Thus, it can be seen from the table of specifications shown in Table 1 that the conditional expressions (1) to (4) and (13) are satisfied in the objective lens system _Lob1 for the parallel stereomicroscope according to the present embodiment.

FIG. 3 is a lateral aberration diagram, an astigmatism diagram, and a distortion diagram in the objective lens system for the parallel stereomicroscope according to the first example. Each of the aberration diagrams is tracked by entering light rays from the side farther from the object Ob (observation optical systems L _R and L _L side), and the light rays passing through the optical axes of the observation optical systems L _R and L _L are used as a reference. Is displayed. In each of these aberration diagrams, y represents an image height, S in the astigmatism diagram represents a sagittal surface, and M represents a meridional surface. Further, the lateral aberration diagram shows the zoom at high magnification, and the astigmatism diagram and the distortion diagram show the zoom at low magnification. In addition, the same symbols as those in this embodiment are used in the various aberration diagrams in all the following examples.

As is apparent from the aberration diagram shown in FIG. 3, it can be seen that the objective lens system L _ob1 for the parallel system stereomicroscope according to the first example is well corrected for aberrations.

(Second embodiment)
The objective lens system L _ob (L _ob2 ) for the parallel stereomicroscope according to the second example will be described with reference to FIGS. 4 and 5 and Table 2. FIG. As shown in FIG. 4, the objective lens system L _ob2 for the parallel stereomicroscope according to the second example is arranged in order from the side far from the object Ob, and has a first lens group G1 having a positive refractive power as a whole, It has a second lens group G2 having a relatively weak refractive power and a third lens group G3 having a positive refractive power as a whole.

  The first lens group G1 includes a biconvex lens L11, a negative meniscus lens L12 having a concave surface facing the object side, and a biconvex lens L13, which are arranged in order from the side far from the object Ob, and has a negative refractive power as a whole. And a lens.

  The second lens group G2 is composed of a plano-concave lens L21 having a plane facing the object side and a plano-convex lens L22 having a convex surface facing the object side, which are arranged in order from the side far from the object Ob, and has a convex surface on the object side as a whole. A meniscus-shaped cemented lens having negative refractive power and a biconvex lens L23, a biconcave lens L24, and a biconvex lens L25 are bonded together to form a cemented lens having a positive refractive power as a whole.

  The third lens group G3 includes a biconvex lens L31 and a planoconvex lens L32 which are arranged in order from the side farther from the object Ob and the plane is directed to the object side.

  Table 2 lists the values of each item in the second embodiment. The surface numbers 1 to 16 in Table 2 correspond to the surfaces 1 to 16 shown in FIG.

Note that the distance between the objective-side optical axes of the observation optical systems L _R and L _L is SBL = 20 mm at the zoom minimum magnification, SBH = 26 mm at the zoom maximum magnification, and the maximum effective diameter of the objective lens system L _ob2 is Dmax = 71 mm. Further, the entrance pupil positions of the observation optical systems L _R and L _L are at a position 43 mm from the first surface of the objective lens system L _{ob2 at} a zoom minimum of 43 mm, a zoom maximum magnification of 242 mm and a position away from the object plane Ob.

(Table 2)
f = 50.2
WD = 31.5
fB1 = -394.0
f1 = 129.6
f2 = 435.2
f3 = 63.4
SBL = 20
SBH = 26
Ymax = 11

Surface number r d nd
νd
1 102.33094 7.500 1.84666 23.9
2 -421.35943 0.500
3 114.20080 3.000 1.83481 42.7
4 32.98856 15.000 1.43425 95.0
5 -209.56031 8.600
6 -35.99216 8.000 1.74950 35.3
7 ∞ 17.000 1.49782 82.5
8 -44.47866 0.500
9 134.37622 14.000 1.59319 67.9
10 -125.00000 3.500 1.83400 37.2
11 125.00000 16.000 1.59240 68.3
12 -110.11690 0.900
13 185.36898 10.500 1.59319 67.9
14 -194.94628 0.500
15 60.31541 13.000 1.59319 67.9
16 ∞
[Conditional expression]
Conditional expression (1) (−fB1) /f=7.85
Conditional expression (2) f1 / f = 2.58
Conditional expression (3) f3 / f = 1.26
Conditional expression (4) νdL1 = 23.9
Conditional expression (5) SBH-SBL = 6
Conditional expression (6) φAP = 25
Conditional expression (7) Ymax / f = 0.219
Conditional expression (13) | f2 / f | = 8.70

Of the values of the conditional expressions shown in Table 2, conditional expression (4) corresponds to the value of the first surface. From the table of specifications shown in Table 2, it can be seen that the objective lens system L _ob2 for the parallel stereomicroscope according to the present example satisfies the conditional expressions (1) to (7) and (13).

FIG. 5 is a transverse aberration diagram, astigmatism diagram, and distortion diagram of the objective lens system _Lob2 for the parallel stereomicroscope according to the second example. As is apparent from the aberration diagram shown in FIG. 5, it can be seen that the objective lens system _Lob2 for the parallel system stereomicroscope according to the second example is well corrected for aberrations.

(Third embodiment)
The objective lens system L _ob (L _ob3 ) for the parallel stereomicroscope according to the third example will be described with reference to FIGS. 6 and 7 and Table 3. FIG. As shown in FIG. 6, the objective lens system L _ob3 for the parallel stereomicroscope according to the third example is arranged in order from the side far from the object Ob, and has a first lens group G1 having a positive refractive power as a whole, It has a second lens group G2 having a relatively weak refractive power and a third lens group G3 having a positive refractive power as a whole.

  The first lens group G1 is composed of a positive meniscus lens L11 having a convex surface facing the object side, a biconvex lens L12, and a biconcave lens L13 arranged in order from the side far from the object Ob, and has a negative refractive power as a whole. And a lens.

  The second lens group G2 includes a negative meniscus lens L21 having a convex surface facing the object side, a positive meniscus lens L22 having a convex surface facing the object side, and a diffractive optical surface D, which are arranged in order from the side far from the object Ob. An element LD, a plano-concave lens L26 having a concave surface directed toward the object side, and a biconvex lens L27 are bonded together to have a cemented lens having positive refractive power as a whole.

  In the diffractive optical element LD, a flat optical glass L23 and two flat optical members L24 and L25 formed from different resin materials are bonded in this order, and the bonding surfaces of the optical members L24 and L25 are joined. A diffraction grating groove (diffractive optical surface D) is formed on the surface. That is, the diffractive optical element LD is a contact multilayer diffractive optical element. In the present embodiment, the joint surfaces of the two optical members L24 and L25 are flat, but the same effect can be obtained even if the diffractive optical surface D is formed as a joint surface having a curvature. Needless to say.

  The third lens group G3 includes a biconvex lens L31 and a positive meniscus lens L32 having a concave surface directed toward the object side, arranged in order from the side far from the object Ob.

  Table 3 lists the values of each item in the third embodiment. The surface numbers 1 to 20 in Table 3 correspond to the surfaces 1 to 20 shown in FIG.

The distance between the objective optical axes of the observation optical systems L _R and L _L is SBL = 20 mm at the zoom minimum magnification, SBH = 26 mm at the zoom maximum magnification, and the maximum effective diameter of the objective lens system L _ob3 is Dmax = 68.45 mm. is there. Furthermore, the entrance pupil position of the observation optical system L _R, L _L is from the first surface of the objective lens system L _ob3 zoom minimum times when 43 mm, the zoom up times when 242 mm, a position away from the object plane Ob.

(Table 3)
f = 50.2
WD = 31.0
fB1 = -420.9
f1 = 166.8
f2 = 756.1
f3 = 59.9
SBL = 20
SBH = 26
Ymax = 11
φLD = 64.23

Surface number r d nd
νd
1 116.46700 7.500 1.84666 23.9
2 -284.85506 0.500
3 142.07687 3.000 1.83481 42.7
4 35.04100 14.481 1.43425 95.0
5 -230.00729 9.576
6 -34.05100 3.745 1.74950 35.3
7 -139.48185 15.336 1.43425 95.0
8 -40.09000 0.500
9 154.98239 14.731 1.59240 68.3
10 -125.00000 4.000 1.90265 35.7
11 126.14143 20.000 1.59240 68.3
12 * -90.02700 0.500
13 179.34654 13.031 1.59240 68.3
14 -178.07559 0.500
15 56.52200 16.000 1.59240 68.3
16 1102.18933

[Diffraction optical surface data]
12th surface κ = 1.0000, A2 = 1.10205E-08, A4 = -6.68539E-12, A6 = 3.87380E-15, A8 = -1.40808E-18

[Conditional expression]
Conditional expression (1) (-fB1) / f = 8.38
Conditional expression (2) f1 / f = 3.32
Conditional expression (3) f3 / f = 1.19
Conditional expression (4) νdL1 = 23.9
Conditional expression (5) SBH-SBL = 6
Conditional expression (6) φAP = 25
Conditional expression (7) Ymax / f = 0.219
Conditional expression (8) nd1 = 1.53
Conditional expression (9) nF1-nC1 = 0.0152
Conditional expression (10) nd2 = 1.56
Conditional expression (11) nF2-nC2 = 0.0111
Conditional expression (12) φLD / φAP = 2.57
Conditional expression (13) | f2 / f | = 15.06

Of the values of the conditional expressions shown in Table 3, conditional expression (4) corresponds to the value of the first surface, and conditional expressions (8) and (9) correspond to the values of the eleventh surface. (10) and (11) correspond to the values of the thirteenth surface. Thus, it can be understood from the table of specifications shown in Table 3 that the conditional expressions (1) to (13) are satisfied in the objective lens system _Lob3 for the parallel stereomicroscope according to the present embodiment.

FIG. 7 is a lateral aberration diagram, an astigmatism diagram, and a distortion diagram of the objective lens system _Lob3 for the parallel stereomicroscope according to the third example. As is apparent from the aberration diagram shown in FIG. 7, it can be seen that the objective lens system _Lob3 for the parallel system stereomicroscope according to the third example is well corrected for aberrations.

  With the configuration as described above, according to the objective lens system for a parallel stereomicroscope according to the present invention, distortion is suppressed to a practically unproblematic level, and the flatness of the image surface is ensured. By correcting well, it is possible to realize excellent imaging performance. As a result, even when a variable magnification optical system is used in combination with this objective lens system, a compact objective lens can be configured even if the field of view and numerical aperture accompanying magnification change are increased. Observation can be carried out.

  In addition, in order to make this invention intelligible, although demonstrated with the component requirement of embodiment, it cannot be overemphasized that this invention is not limited to this.

L _ob (L _{ob1 to} L _ob3 ) Objective lens system for parallel system microscope G1 First lens group G2 Second lens group G3 Third lens group L11 to L32 Constituent lens B1 first lens for parallel system microscope Bonded lens with negative refractive power that constitutes a group LD Adhesive multilayer diffractive optical element D Diffraction optical surface

Claims (6)

Arranged in order from the far side from the object,
A first lens group including a cemented lens having a negative refractive power and having a positive refractive power as a whole;
A second lens group having a weak refractive power, including a meniscus lens having a negative refractive power with a convex surface facing the object side, and a cemented lens having a positive refractive power;
An objective lens system for a parallel system stereomicroscope including at least one single lens having a positive refractive power and composed of a third lens group having a positive refractive power as a whole,
When the focal length of the cemented lens having the negative refractive power constituting the first lens group is fB1, and the focal length of the entire objective lens system is f, the following expression 1.00 <(− fB1) / f <20.00
An objective lens system for a parallel stereomicroscope characterized by satisfying the following conditions. The first lens group includes a single lens having a positive refractive power,
When the Abbe number of the single lens having the positive refractive power constituting the first lens group is νdL1, the following equation νdL1 <40.0
The objective lens system for a parallel stereomicroscope according to claim 1, wherein the following condition is satisfied. The meniscus lens having negative refractive power that forms the second lens group and has a convex surface facing the object side is a cemented meniscus lens in which a negative lens and a positive lens are bonded together,
3. The objective lens for a parallel system stereomicroscope according to claim 1, wherein the cemented lens having a positive refractive power is a cemented lens in which three lenses of a biconvex lens, a biconcave lens, and a biconvex lens are bonded together. system. This is an objective lens system for a parallel stereomicroscope that converts a light from an object into a parallel light beam and then guides the light beam to the subsequent two observation optical systems for the left eye and the right eye to enable stereoscopic viewing. And
The observation optical system includes a variable magnification optical system, the distance between the objective side axes at the zoom maximum magnification of the variable magnification optical system is SBH, and the distance between the objective side axes at the zoom minimum magnification of the variable magnification optical system is When SBL is satisfied, the following condition is satisfied: 1 ≦ SBH−SBL ≦ 10
When the maximum exit pupil diameter on the left and right sides of the objective lens system is φAP, and the maximum object height that can be observed by the objective lens system is Ymax, the following expression 23 ≦ φAP ≦ 30
0.160 ≤ Ymax / f
An objective lens system for a parallel stereomicroscope characterized by satisfying the following conditions. The objective lens system enables stereoscopic viewing by converting light from an object into a parallel light beam and then guiding the light beam to two subsequent observation optical systems for the left eye and the right eye. ,
The observation optical system includes a variable magnification optical system, the distance between the objective side axes at the zoom maximum magnification of the variable magnification optical system is SBH, and the distance between the objective side axes at the zoom minimum magnification of the variable magnification optical system is When SBL is satisfied, the following condition is satisfied: 1 ≦ SBH−SBL ≦ 10
When the maximum exit pupil diameter on the left and right sides of the objective lens system is φAP, and the maximum object height that can be observed by the objective lens system is Ymax, the following expression 23 ≦ φAP ≦ 30
0.160 ≤ Ymax / f
The objective lens system for a parallel stereomicroscope according to claim 1, wherein the following condition is satisfied. The second lens group includes a contact multilayer diffractive optical element having a diffractive optical surface in which two diffractive element elements made of different optical materials are bonded and a diffraction grating groove is formed on the bonded surface.
Of the two diffractive element elements made of the different optical materials, the refractive indices for the d-line, F-line, and C-line of the diffractive optical element having the lower refractive index and higher dispersion are nd1, nF1, and nC1, respectively. The refractive indexes of the optical material of the diffractive optical element having the higher refractive index and lower dispersion with respect to the d-line, F-line, and C-line are nd2, nF2, and nC2, respectively, and the effective diameter of the diffractive optical surface of the diffractive optical element is φLD. When the maximum exit pupil diameter on the left and right sides of the objective lens system is φAP,
nd1 ≦ 1.54
0.0145 ≦ nF1-nC1
1.55 ≤ nd2
nF2-nC2 ≦ 0.0130
2.2 ≦ φLD / φAP
5. The objective lens system for a parallel stereomicroscope according to claim 1, wherein the objective lens system according to claim 1 is satisfied.

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