JPH0358010A - Microscope reflecting objective - Google Patents

Abstract

PURPOSE:To obtain the reflecting objective which has its spherical aberration compensated excellently by using only spherical surfaces by arranging all of 1st -4th reflecting mirrors symmetrically about an axis, giving the 1st reflecting mirror a positive power and the 4th reflecting mirror a negative power, and making their surfaces all spherical. CONSTITUTION:The 1st reflecting mirror M1, 2nd reflecting mirror M2, 3rd reflecting mirror M3, and 4th reflecting mirror M4 are all arranged symmetri cally about the axis in the order of incidence of light from a sample. Then the 1st reflecting mirror M1 has a positive power, the 4th reflecting mirror M4 has a negative power, and the reflecting surfaces are all spherical. When the reflecting objective has two surfaces with power, the spherical aberration can not be compensated sufficiently by a spherical system. Three reflecting surfaces, however, are provided to compensate the spherical aberration almost completely even by the spherical system. When light is reflected three times, the object point and image point are formed on the same side, so the number of times of reflection is increased to four.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a low-magnification reflective objective mirror used in photometric microscopes and stage scanning type scanning microscopes. [Prior Art] As an optical system having a configuration similar to the microscope reflecting objective mirror of the present invention, Japanese Patent Publication No. 47-1 2508 and Japanese Patent Application Laid-Open No. 47-248
No. 33, JP-A-59-77403, JP-A-47-12
Optical systems described in each publication of No. 4311 are known. All of these conventional examples have two reflecting surfaces with power. [Problems to be Solved by the Invention] In these conventional examples, since there are two reflecting surfaces that have power, if these two surfaces are spherical surfaces, spherical aberration cannot be corrected. Furthermore, if one surface is made aspherical, spherical aberration is almost completely corrected, but ``aspherical surfaces are more difficult to manufacture than spherical surfaces, and are difficult to achieve precision, so they cannot be used much in practice.

An object of the present invention is to provide a reflective objective for a microscope in which spherical aberration is well corrected using only spherical surfaces. [Means for Solving the Problems] The reflective objective mirror of the present invention has first reflective @M. ．． Second reflection 11L. Third Reflection II Ms
．． In an optical system in which all fourth reflecting mirrors M4 are arranged axially symmetrically, the first reflecting mirror M, has positive power, and the fourth reflecting mirror M,
4 has negative power, and all reflecting mirrors are spherical. Reflecting objectives, including those of telescopes, have two surfaces with power, the primary mirror has positive power and the secondary mirror has negative power, in order to correct spherical aberration. In order to do this, the negative spherical aberration generated by the primary mirror with positive power is canceled by the positive spherical aberration generated by the secondary mirror with negative power. However, because the negative power is much stronger than the positive power, spherical aberrations cannot be sufficiently corrected in a spherical system. Therefore, by having three or more reflective surfaces with power, it is possible to almost completely correct spherical aberration with just a spherical system, but when the number of reflections is three, the object point and image point are on the same side, so the microscope For a reflective objective, the number of reflections must be 4 degrees. Therefore, in the present invention, the number of reflections is set to four, that is, the first to fourth reflecting mirrors are used as described above, and the first reflecting mirror h has a positive power. The fourth reflecting mirror M4 has negative power, and the second reflecting mirror h and the third reflecting mirror Ms
The spherical aberration is effectively corrected by having the main role of correcting aberrations. Paraxial quantities (magnification, focal length, image position, etc.) are determined by the power ratio of the first reflecting mirror M1, which is the first reflecting mirror that the light from the specimen hits, and the fourth reflecting mirror M4, which is the last one that the light from the specimen hits. ■3 and third reflection 11M. is mainly the fourth reflection t
liM. The purpose of this is to increase the Z component of the direction cosine of the light ray that enters the envelope, and to correct spherical aberration. Third reflection IIMt. The absolute value of the power of Ms is 1st. Fourth reflecting mirror M+. It is smaller than the absolute value of the power of M4, and the following condition (1). It is preferable that (2) is satisfied. (l) 1φ81≦0.2 (2) 1φs1≦0.2 However, φ1φ3 is $, respectively: f・(2/r*), 1s
=f・(2/rsl), where the focal length of the microscope reflecting objective, ri+f''* is the radius of curvature of the reflecting surface of the second reflecting mirror 11L and the third reflecting mirror M3, respectively. If these conditions (1) (21) are not met, the second reflecting mirror Ml
The power of the third reflecting mirror MS becomes too strong and the spherical aberration becomes overcorrected. Another third reflection! I MY FIRST REFLECTION 11M. When approaching , the third reflection of the ray with a small NA! The height of the ray in the US becomes lower, the marginal ray reflected by the fourth reflecting mirror M4 is more likely to be rejected by the third reflecting mirror, and the concealment rate increases. Therefore, in order to reduce the concealment rate, The third reflecting mirror 11s must be kept away from the l-th reflecting mirror ■1. However, with a low-magnification objective mirror, the focal length is long, so the third
The reflector M3 tends to approach the l-th reflection tau+, which is contrary to the direction of decreasing the concealment rate. Conversely, a high-magnification objective mirror has a short focal length, so the third reflecting mirror M
, tends to get closer to the second reflected raMs, but if it gets too close, the concealment rate increases. Therefore, the third reflecting mirror M
Position 3 corresponds to the magnification (focal length M) and its associated N
A must be within a certain range, and the following condition (3)
) is preferable. (3) 0.01≦(
1Δ-. 1・fl /L”≦o.i However, 1Δ.H+B
l is the mechanical distance on the axis between the first reflecting mirror and the third reflecting mirror, f is the focal length of the microscope reflecting objective, and L is the optical distance from the specimen of the microscope reflecting objective to the first reflecting mirror. This is the target distance. [Examples] Next, examples of the microscope reflecting objective mirror of the present invention will be shown. ? Example l f=20.45 (IOX). NA=0.3 Concealment rate=
49%. WFA=0.002ro=(1) d0=59.957 r+=-72.673 d+=-37.030 r■=-245. 472 da=31.735 ra=■ da--19.662 r. = −135.812 d. =25.0 r1■ L=59.95? , φ■=0.167(1Δ
MIM3 1・f)/L2 = o. o3o Example 2 f = 4.079 (5QXl. NA = 0.6 Concealment rate = 42%. WFA = O.Ol2ro = ■ Nmaru I. = 210 = O I. = 210 d. = 38.026 r + = -42.132 d.=-32.341 rx=-3416-091 dz= 7.257 ra=■ d.=-2.755 r4=-10.271 (L=49.813 rs= (1) L = 38.026.φ,=o.ootz
(1ΔMIM31·f)/L2 = 0.071 Example 3 f = 4.09 (50X). NA=0.6. Concealment rate=42%, llFA=o. 011ro” ■ =O I.= 210 do=38.778 r+=-42.897 d.=-31.292 r3=ω a,=6.981 rs= 1630.314 di=-4.8LS r4=- 10.294 d.= 50.347 r.=ω L= 38.778. 1φ*l=o, I
φ3{1ΔMIk431・f)/L2 =0.066
Example 4 f = 2.597t80X). NA=0.65
．． Concealment rate = 42%. WFA=0.047λro
=■: 0.0G25 e. = 210 d. = 29.943 r+=-35.184 d. =+= -14.931 rz=-143.845 d*= 10.011 r3" (1) ds=-8.634 r4=-9.338 d4= 53.622 rs= ■ L=29.943. lφzl=0.036
. lφs1=0(1ΔMIM31・f)/L2
=0.043 Example 5 f=2.25, NA=0.65. I. =■ Concealment rate = 42%. Stomach FA = 0.048 nro
=ω d. = 28.422 r+=-33.757 d. =-23.22 rx=-113.118 d. = 11. lfs9 r,=■ d. = −11. f) 34 r. =-9.721 d. = 54.644 rs= ■ L= 28.422. φ2 depth 0.04
(1ΔIIIM31・f)/L2 = ro, ro34φ,
1 = 0 Example 6 f = 2.091 (IOOXI Concealment rate 42% ro = ■ NA = 0.7 WFA = 0.077 λ Io"210 do = 27.524 r, = -32.864 d. = =-22.524 r*= -101.946 d1χ11.817 rs= (1) ?3 wealth-11.817 r4=-9.663 a4=ss.o rS=ω L”27.524.l$il =0.041
．． Lesl=0(1ΔMIM31・f)/L2
= 0.03 where rl+ rl+ ”・ is the radius of curvature of each reflecting surface, dd,... is the distance between each reflecting surface, r0 is the specimen surface + rS is the trunked surface. Also, the concealment rate in the data is (NA- + -/NA.■)2.It should be noted that NA■■
N.A. ■ is as shown in Figure 13. Among these Examples, Example 5 is an optical system designed for infinite distance. This aberration curve diagram shows what happens after an aberration-free lens with f=180 is added. Furthermore, the wavefront aberration (WFA) in the data is an on-axis value that takes into account the concealment rate, and the evaluation plane is different from the aberration curve diagram. In other words, the aberration curve diagram is
The values are shown for the sample plane by tracing back from the number of fields of view. [Effects of the Invention] Although the microscope objective mirror of the present invention is composed of only spherical surfaces, spherical aberration is extremely well corrected.

[Brief explanation of drawings]

1 to 6 are embodiments 1 to 6 of the present invention, respectively.
7 to 12 are aberration curve diagrams of Examples 1 to 6, respectively, and FIG. 13 is a diagram showing the basic configuration of the present invention.

Claims (1)

[Scope of Claims] (1) In an optical system in which a first reflecting mirror, a second reflecting mirror, a third reflecting mirror, and a fourth reflecting mirror are all arranged axially symmetrically in the order in which light from the specimen hits, A microscope reflecting objective mirror characterized in that a first reflecting mirror has a positive power, a fourth reflecting mirror has a negative power, and all surfaces are spherical. (2) The microscope reflecting objective according to claim 1, wherein the surface powers φ_2 and φ_3 normalized by the focal lengths of the second reflecting mirror and the third reflecting mirror satisfy the following conditions, respectively. (1) |φ_2|≦0.2 (2) |φ_3|≦0.2 where φ_2=f・(2/r_2), φ_3=f・(2
/r_3) where f is the focal length of the reflecting objective, r_2, r_
3 is the radius of curvature of the surfaces of the second and third reflecting mirrors, respectively. (3) The third reflecting mirror is located between the first reflecting mirror and the second reflecting mirror, and the mechanical distance ΔM_1_3 on the axis of the first reflecting mirror and the third reflecting mirror satisfies the following conditions. The microscope reflecting objective according to claim (1), which satisfies (3). (3) 0.01≦(｜ΔM_1_3・f)/L^2≦0
．． 1 where L is the optical distance from the specimen surface of the reflecting objective to the first reflecting mirror.