JPS6231817A - Microscope objective lens - Google Patents

Abstract

PURPOSE:To correct not only the aberration of the basic wavelength but also the color aberration with a simple constitution by making the second lens of three group lens constitution into the refraction factor distributing type lens in which the dispersion of the periphery are larger than that of the center of the lens. CONSTITUTION:In the constitution of the first and second refraction factor distributing type lenses and the third lens, the magnification is secured by the strong positive refraction force of the first lens and the image surface curving is corrected at strong curvature surface. The color aberration on the negative axis generated at the first lens is corrected by the second lens in which the dispersion of the periphery are larger than that of the center of the lens, and at the position where the beam height of the aperture beam to image-form the image point on the axis is the highest, the second lens is positioned. Consequently, with a very simple constitution, not only the aberration of the basic wavelength but also the color aberration are corrected sufficiently, and the lens system of the high performance can be obtained.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a microscope objective lens, which includes, as at least one element in the lens system, a gradient index lens whose refractive index changes according to the radial distance from the optical axis. The present invention relates to a microscope objective lens using a microscope objective lens.

[Conventional technology]

As requirements for a microscope objective lens, it is desired that various aberrations be well corrected and that the numerical aperture (NA) be large in order to obtain high resolution.

In addition, in order to avoid collision with the specimen, the working distance (WD)
) is preferably large. On the other hand, there are constraints on the length of the lens system due to the need to replace and use various objective lenses, and constraints on keeping the distance to the image plane constant. Furthermore, in a normal microscope optical system, if chromatic aberration is not sufficiently corrected, color bleeding will occur and the image will be difficult to see.

It is extremely difficult to satisfy all of these conditions, in addition to the fact that the lens system is a magnifying system.

Conventionally, in order to overcome the above-mentioned difficulties and construct a microscope objective lens that satisfies the various requirements mentioned above, the objective lens had to have an extremely large number of lenses, and also had anomalous dispersion such as debit. optical materials and a large number of cemented lenses.

By the way, when configuring an optical system, it is generally done by combining a large number of lenses, but it is well known that non-yellow lenses made of only spherical lenses or gradient index lenses can be used to improve the aberration correction ability. be. Furthermore, regarding the correction of chromatic aberration, it is known that chromatic aberration can be corrected by controlling the refractive index distribution with respect to the wavelength at the center of the lens. -28057 Publication and Special Publication No. 57-39
There is a publication No. 405.

The former of these publications does not mention anything about aberration correction, and the latter describes correction of off-axis aberrations using a gradient index lens, but does not mention correction of chromatic aberrations. No 0 [Problems to be solved by the invention] The present invention provides a microscope that corrects not only fundamental wavelength aberration but also chromatic aberration using a gradient index lens whose refractive index changes according to the radial distance from the optical axis. objective lens.

[Means for solving problems]

In order to solve the above problems, the present invention disposes at least one gradient index lens whose refractive index changes according to the distance in the radial direction from the optical axis in a lens system. This is a microscope objective lens in which the dispersion around the lens is higher than the dispersion at the center of the lens.

The microscope objective lens of the present invention has a first group lens having a positive refractive power on the head side from the object side, and a small height (both half of It is composed of a second group lens and a third group lens, which are positioned in a range having a height, and at least the second group lens has a refractive index gradient according to the distance in the radial direction from the optical axis as described above. This is a lens system composed of a gradient index lens in which the dispersion at the periphery of the lens is smaller than the dispersion at the center.

Normally, a microscope objective lens must be sufficiently corrected for spherical aberration, coma aberration, field curvature, astigmatism, and the like. Among these aberrations, correction of field curvature and astigmatism in particular places stricter restrictions on other aberrations, making it difficult to satisfactorily correct all of these aberrations.

Furthermore, in order to correct chromatic aberration, the design must take into account the didispersion of the refractive index of the glass used to some extent from the beginning, and this imposes significant restrictions on aberration correction.

Normally, chromatic aberration is corrected by the distance between two curvatures of the refractive surfaces.

This is done by controlling the refractive index didispersion, etc., but if a gradient index lens is used, it can also be done by further controlling the dispersion distribution, that is, the refractive index distribution for each wavelength. For example, it is derived from aberration theory that Hosochi chromatic aberration, which is the basis when considering chromatic aberration, can be completely corrected by controlling the radius of curvature and the refractive index distribution of each wavelength in a gradient index lens, even though it is a single lens. It's dark. Such an effect cannot be expected with a homogeneous lens system, and shows the great ability to correct chromatic aberration by using a gradient index lens.

By the way, when correcting chromatic aberration using a gradient index lens in a microscope objective lens, it is advantageous for correcting chromatic aberration if the axial image point is placed at a position where the ray height of the aperture ray that forms the image is highest.

Normally, correction of chromatic aberration requires correction of axial chromatic aberration and lateral chromatic aberration, but lateral chromatic aberration relates to off-axis performance. In a normal microscope objective lens, the off-axis principal ray is propagated without departing greatly from the optical axis, so the effect of correcting chromatic aberration of magnification using a gradient index lens is
This is slightly lower than the correction effect for chromatic aberration. For this reason, the chromatic aberration of magnification can be effectively corrected by using other parameters, and by mainly correcting the chromatic aberration by controlling the refractive index distribution for each wavelength.

Therefore, it is preferable to arrange the gradient index lens at the above position where the behavior of the light beam can be effectively controlled. Therefore, as described above, the present invention has a three-group structure consisting of the first group lens in front of the gradient index lens, the second group lens of the gradient index lens, and the third group lens arranged after the gradient index lens. .

The first group lens needs to have strong refractive power to ensure magnification, and is often constructed of a lens having a surface with strong curvature to correct field curvature. If the first group lens is configured as such and has a positive refractive power, a large negative chromatic aberration will occur in the first group lens.

In order to correct this negative Hosochromatic aberration, the refractive index of the gradient index lens in the second group lens must be adjusted in the radial direction from the optical axis, where the dispersion around the lens is larger than the dispersion at the center of the lens. Positive chromatic aberration can be generated and corrected using a variable refractive index gradient lens.

Conversely, if the dispersion around the lens is smaller than the dispersion at the center of the lens, negative Hosotchi chromatic aberration will occur, and to correct this, the lens group on the image side of the second lens group must have a complex configuration. This is extremely disadvantageous.

The same chromatic aberration correction effect can be obtained by using a gradient index lens as described above in a range having a height at least half of the height where the ray height of the aperture ray that forms the axial image point is the highest. be able to.

Furthermore, by using a refractive index distribution lens at a position closer to the image than the position where the off-axis ray intersects with the optical axis, it becomes possible to easily correct chromatic aberration of magnification, which was previously corrected by parameters other than the refractive index distribution. .

〔Example〕

An embodiment of the present invention (configuration shown in FIG. 1) described in detail above will be described below.

f=l, NA=0.46, β=20X
WD=0.2265, f+=4.895,
Δ=11.32 +r, = 0.4325 dl” 0.8270 no+ = 1.8340
0 νo+ = 37.16rz= 0.7311 d2=o, o119 rs ” 2.8175 da=o, 7471 not=1.72600 ν
02 = 53.54 (11) r, = -5,037
1 d, = 3.2187 rs" 2.3789 ds" 0.1472 nos = 1.5163
3 νas = 64.14 (*)ra: 3.
2099 2nd group lens λ (nm) n, n258
7.56 -0.6449JX10-' 0.155
29X10-2656.28 -0.67774X10
-1 0.26729X10-'486.13-0.5
6174X10-10.57479X10-2 3rd group lens λ n, n2587.56
-0.26784 0.20944656.2
8 -0.26756 0.20946486
．． 13 -0.26793 0.20855 However, rlp r2 p...t re is the radius of curvature of each surface, dB r d2p..., da is the thickness and air spacing of each lens, n01 * n02 y n03 is the refractive index of each lens (for gradient index lenses marked with an asterisk, the refractive index at the center), ν. 1, ν. 2. ν0
．． is the Atsube number of each lens, f is the focal length of the entire system, and f
+ is the focal length of the first group lens, NA is the numerical aperture, β is the magnification, WD is the working distance, and Δ is the Atsube number at the center of the gradient index lens used for the second group lens and 0.0 from the optical axis.
If Δ is positive in terms of the difference in Abbe numbers at positions 5 apart, the dispersion around the lens will be larger than the dispersion at the center of the lens.

For gradient index lenses, the radial distance from the principal axis is p
When one wavelength is λ, the refractive index of each wavelength has a distribution expressed by the following equation.

n(λ)=no(λ)+nt(λ)? 2+n2(λ)9
4+...Here, no(λ) is the refractive index for the wavelength λ at the center of the lens, nl(λ), n=(λ),... are the quadratic term, quartic term, etc. for ψ, respectively. It is a coefficient for wavelength λ. The above data shows the distribution coefficients for the d, C, and F lines.

In this example, as shown in the data, the third group is also a gradient index lens.

〔Effect of the invention〕

As explained above in detail and shown in the examples, the microscope objective lens of the present invention has an extremely simple structure, but is a very high-performance lens system that sufficiently corrects not only fundamental wavelength aberration but also chromatic aberration. is 0

[Brief explanation of the drawing]

FIG. 1 is a sectional view of an embodiment of the present invention, and FIG. 2 is an aberration curve diagram of the above embodiment.

Claims (2)

[Claims] (1) In order from the object side, the first group lens having positive refractive power is positioned in a range having a height at least half of the height at which the ray height of the aperture ray that forms the axial image point is the highest. A gradient index lens consisting of a second group lens located on the image side, and a third group lens located on the image side, where the second group lens has a gradient of refractive index according to the distance in the radial direction from the optical axis. A microscope objective lens characterized in that dispersion is larger at the periphery of the lens than at the center of the lens. (2) The microscope according to claim (1), wherein the second group lens of the gradient index type is arranged at a position where the ray height of the aperture ray that forms an axial image point is the highest. objective lens.