JPS6057315A - Wide-visual field eyepiece lens - Google Patents

Abstract

PURPOSE:To improve the capacity with simple constitution by constituting a lens system with the first positive lens, the second biconcave negative lens, the third positive lens, and the fourth positive lens having a higher-curvature surface directed to the incidence side, which are arranged in order from the light incidence side, to satisfy specific conditions. CONSTITUTION:The lens system is provided with the first positive lens L1, the second biconcave negative lens L2, the third positive lens L3, and the fourth positive lens L4 whose surface having a higher curvature is directed to the incidence side, and these lenses are arranged in order from the light incidence side, namely, the side of a space image I . The lens system is constituted to satisfy conditions of formulas I -IV where focal lengths of the whole of the system, the second lens, and the fourth lens are denoted as F, f2, and f4 respectively and the resultant focal length of the first-the third lenses is denoted as F' and the radius of curvature in the eye side of the fourth lens is denoted as r8. If these conditions are satisfied, a wide-visual field eyepiece lens is obtained which has a small distortion and has the spherical aberration of the pupil compensated well and is superior in flatness of the image surface and has a simple constitution.

Description

[Detailed description of the invention] (Technical field of invention) The present invention relates to a wide field eyepiece for a microscope.

(Background of the Invention) Most conventional eyepiece lenses were composed of a positive single lens or a cemented lens, and therefore had a large Pennog-Rir sum and residual field curvature, and also had large distortion. . In the case of microscopes used in the biological field, the target specimens are often thick, transparent specimens, and their shapes are irregular. There were no problems. However,
With the recent development of IC chestnuts, microscopes are increasingly being used in the inspection process. These specimens are different from specimens used in the biological field, in that they are often flat specimens that are observed using reflected light, and they are made up of a series of fine regular patterns.

Therefore, when observing these objects, it is necessary to minimize the field curvature and distortion of the optical system. In a microscope optical system, when comparing the distortion aberrations of the objective lens and the eyepiece lens, it is generally found that the distortion aberration of the eyepiece lens remains larger, and there has been a desire to improve the eyepiece lens.

For this reason, eyepiece lenses based on the triplet type lens, which is well known as a photographic lens, have been developed, for example, in Japanese Patent Application Laid-open No. 54
It is known from the publication No.-154342. This eyepiece lens had a lens with a strong negative refractive power, so that the Petzval sum was small and astigmatism and coma aberration were well corrected.

However, with this eyepiece lens, several distortion aberrations still remain at the maximum angle of view, and correction of spherical aberration of the pupil is still not sufficient. The spherical aberration of the pupil is the amount of deviation in the optical axis direction due to the angle of view when the exit pupil of the objective lens is imaged at the eyepoint position by the eyepiece lens. That is, this means that the eye point position differs depending on the angle of view. If the spherical aberration of the pupil is large, the optical flux near the peripheral, middle, and central portions of the visual field will not be converged at the same position, and in severe cases, crumpling will occur in the visual field.

(Objective of the Invention) An object of the present invention is to provide a wide-field eyepiece with a simple structure, which has small distortion, good correction of spherical aberration of the pupil, and excellent flatness of the image surface. be.

(Summary of the Invention) As shown in FIG. 1, the wide-field eyepiece according to the present invention comprises, in order from the light incident side, that is, the aerial image 1 side, the first V7 lens (L) of the positive lens, the first V7 lens (L) of the biconcave negative lens, and 2 lenses (L,
), a third lens (L, ) which is a positive lens, and a fourth lens (L4) which is a positive lens with a surface having a stronger curvature facing toward the incident light side. Then, the overall focal length is F1, the focal length of the second lens (L, ) and the fourth lens (L,) is f, fa, and the composite focal length of the first to third lenses is F.
', and the radius of curvature of the lens surface on the exit light side, that is, on the eye side, of the fourth lens (,L,) is r, then +1.5F < l fl l'< (1,8F (
1'10.9F < f, < 1.4F (2"10.
1F"< f, <0.5F'(3)-O,'7 (
F/r, < 0.7 It satisfies each condition (4).

The eyepiece of the present invention is also based on a so-called triplet type lens, but its main feature is that the positive lens closest to the exit light side, that is, the fourth lens (+, , ), has a relatively small refractive power. It is something to do. That is,
In the eyepiece disclosed in Japanese Patent Application Laid-Open No. 54-154342, the refractive power of the positive lens closest to the eye is strong, and the convex surface is directed toward the eye.
Even if the distortion generated here cannot be canceled out by the negative lens located immediately before it, it tends to remain.
It was discovered that the spherical aberration of the pupil was undercorrected due to the strong positive refractive power on the eye side.
In order to make these improvements, we have found the necessary optimal conditions as described above.

Each of the above instructions will be explained below.

Equation (1) relates to the power of the negative lens as the second lens. This negative lens is necessary to correct distortion aberration, secure eye-leaf (eye distance), and correct field curvature, that is, to reduce Petzval sum. If the lower limit of this condition is exceeded, the power of the negative lens will become too strong, and the meridional image plane and distortion will become too positive, and even when corrected with a positive lens as the fourth lens, the distortion will be U near the maximum angle of view. Causes a bend to turn. , Also, the spherical aberration of the pupil becomes too positive. On the other hand, if the upper limit is exceeded, the power of the negative lens becomes too weak, the Petzval sum increases, and the field curvature increases. Furthermore, since the divergence effect of the luminous flux becomes smaller, the eye leaf also becomes smaller.

Equation (2) relates to the power of the positive lens as the fourth lens. This positive lens, along with the negative lens of the second lens, is used to improve I (lance) for correcting field curvature and distortion aberration. Negative distortion is generated in order to cancel the distortion.When the lower limit of this condition is exceeded, the power of the positive lens becomes stronger, and the power of the combination of the first to third lenses becomes relatively weaker. , lateral chromatic aberration will be undercorrected. Furthermore, although it is related to the ranges of conditional expressions (6) and (7) described later, it is difficult to correct the condition using a single lens even if existing glass types within this range are used. However, the distance between the image plane and the lens becomes shorter, and scratches on the lens surface become more noticeable. On the other hand, if the upper limit of the condition is exceeded, the power of the positive lens becomes too weak and the meritional image plane moves in the positive direction to a greater extent than the distortion, so if this is canceled by the second negative lens, the distortion cannot be canceled out and remains.

Conversely, if the distortion aberration is canceled, the meridional image surface becomes too negative and the spherical aberration of the pupil becomes excessive.

Equation (3) relates to the power ratio between the combination of the first to third lenses and the fourth lens. If the lower limit is exceeded, the positive power of the fourth lens becomes relatively too strong, and (2) r'i
7) As in the explanation, the chromatic aberration of magnification is undervalued, and it is simply /
Correction is difficult with a configuration that only includes

On the other hand, if the upper limit is exceeded, the positive power of the fourth lens becomes relatively weak, making it difficult to balance the meridional image plane and correction of distortion aberration. In other words, changes in the power of the fourth lens greatly affect the meridional image plane)! l'L, 1st
~Changes in the combined power of the third lens do not significantly affect distortion, so unless the power of the fourth lens and the combined power of the first to third lenses satisfy the above conditional expression (3), aberrations will occur. It becomes difficult to maintain a balance.

Equation (4) relates to the curvature of the eye-side lens surface of the fourth lens. If the lower limit of this condition is exceeded, the positive refractive power for the eye becomes strong, and the distortion aberration and noridional image surface become too positive. In particular, the distortion aberration rapidly moves in the positive direction as the angle of view increases, and even if the second negative lens cancels out the distortion at the maximum angle of view, a large amount of intermediate distortion remains.

When this is actually observed, the middle part of the visual field has a pincushion distortion.
The peripheral portions end up with undesirable barrel distortion. On the other hand, if the upper limit is exceeded, the positive refractive power for the eye becomes weaker, and the distortion and meridional image plane become too negative. Even when distortion is corrected by the first to third lenses, the meridional image plane remains large and negative. In addition, the spherical aberration of the pupil moves significantly in the positive direction, the eye point position differs depending on the angle of view, and the principal point moves closer to the image side, so the eye relief itself becomes shorter, which is inconvenient during observation.

In the configuration of the present invention as described above, the second lens and the third lens
When the air distance with the lens is d4, and the Atsube numbers of the second and fourth lenses are ν1 and ν4, respectively, 0.081f, l < d, < 0.221f, l
(5) It is desirable to satisfy the following conditions: <30 (6) ν, >45 (7).

The condition of equation (5) is related to the focal length f of the negative lens as the second lens and the distance (14 ratio) between the second lens and the third lens.If d6 exceeds the lower limit, that is, the second lens When the distance between d4 and the third lens becomes smaller, the light beam bounced up by the concave lens of the second lens is converged by the positive lens of the third lens before it rises much, resulting in a shorter eye relief. If it is too small, the second lens and third lens will collide,
I can't do less than this. On the other hand, when d exceeds the upper limit, that is, when the distance between the second lens and the third lens becomes large, the chromatic aberration of magnification becomes insufficiently corrected, and it is difficult to correct it with existing glass types if a single lens is used. In addition, the distance from the image plane to the first lens becomes small, and scratches and dirt on the lens surface become noticeable, which is unfavorable for observation.

Equations (6) and (7) mainly relate to correction of lateral chromatic aberration. Equation (6) defines an appropriate range of the Abbe number of the negative lens as the second lens. In this configuration, there is only one negative lens and there is no cemented lens, so unless the Abbe number of the negative lens falls within the range of formula ω), the chromatic aberration of magnification cannot be corrected completely. Equation (7) defines an appropriate range of the Abbe number of the positive lens as the fourth lens. In this configuration, there are three positive lenses, but the positive lens as the fourth lens is most effective against lateral chromatic aberration. Therefore, unless the Abbe number of the positive lens as the fourth lens is within the above range, the chromatic aberration of magnification cannot be corrected completely.

In addition, in this configuration, if either the first lens or the fourth lens is a cemented lens, the range of equations (6) and (7) will be wider, but in order to have an inexpensive and simple configuration, It is desirable to leave it as a single lens and satisfy the above range.

(Example) Examples according to the present invention will be described below.

Each of the embodiments satisfies all of the above-mentioned conditions f'l2 of the present invention. The first embodiment has an extremely simple configuration as follows. That is, the 8151 to 4th lenses are all formed of a single lens, the 3rd lens and the 3rd lens are the same, and the negative lens as the 2nd lens is a biconcave lens with the same absolute value of the radius of curvature on both sides, The eye-side lens surface of the fourth lens is a flat surface. Furthermore, the glass types of the three positive lenses are the same. Therefore, out of a total of 8 polishing surfaces, there are only 4 types of curvature prototypes and plates other than flat surfaces, which reduces the number of types of tools and significantly reduces the number of man-hours.

The specifications of the first to fourth embodiments according to the present invention are shown in the table below. However, I',, r,, r,... represent the radius of curvature of each lens surface sequentially from the incident light side, that is, the objective lens side, and dd,, d,,... are the center thicknesses of each lens. and air spacing, nl, n, . . . are the d-line of each lens (λ=587.
6 nm), the refractive indexes ν1, ν, . . . represent the Abbe number of each lens. In addition, the focal length of each example is 25°, the angle of view is 20) = 44°, and it is co-conducting.
is the Pentuval sum, and EP represents the eye relief (ocular distance, that is, the distance from the apex of the final lens surface in terms of the eye point).

(First Example) P=0.024 EP=21.1 ” ” ”9”'(Il”'5.5 11+ ””
1.713 1'l -54,0r, =-35,4 d, =4.3 r, --27°Od, =3. On, =1.784
7 11. =25.8rl = 2.7.0 da ”'2. (+ r, = 5'J, 3 rl = -35,4" = 5.5 11+ , = l, 7
13 ν, =54. Od = 0.8 r, = 21.4 r, = ωdy = 6. On4 = l, 713 ν,
=54.0 (Second Example) P=0.025 EP=19.2 r, = 28.6 r, , :36. (l d, ==8.Q' nl
``1.6968 shi, =55.6d, =2.6 r, = 28, Or r, :I B, B d-2 1.5 fl+ ``''1.
7408 ν+ ”27.6d, =2.4 rs=45.4 r, =-42,3ds =5.0 nl =1.62
04 1/, =60.34 =0.2 r, = , 17.1 r, = 87.0'' =5, On, =1.713
ν, =5'4. Q (Third Example) p=Q, 925 E P = 19.6r'-37°7
d,=8. Q n1=1.6385 p, -55,5r
l =-28,5 d, =3.0 r, =-22,3 r4=26. B d, =1.5 rb =1.78
47 ν# =2(i, 1at -1,8 rv-57,0 ,, ==-36,46I"4.5 0+ =1.717
νs =48.1d, =0.2 rv ”” 19.3 r, =] 4o, o d, =6.7 n, =1.
717 ν, = 48.1 (4th example) P = 0.025 E P = 21.0” ” 4
cL =5.5 III =1.713 1'l =5
4. Or, =-34,Q City=4.3""-2" d-=3.On= =1.7552 h
=27.6r, =26.0 (L =2.0 rg=59°3dI=5.5 nI=1.713 1'
,=54. Ore = 35.4 d, =0.8 rv-20°5d, =6. On, =1.6583
v, =57.3r, =-500,0 Corresponding values of the above conditional expression according to the present invention in each of the above first to fourth embodiments are shown in the table below.

Aberration diagrams of the first to fourth embodiments are shown in FIGS. 2 to 4, respectively. Each aberration diagram shows the spherical aberration of the pupil (PSp
H) as the reference beam (1 line (λ-587, Gnm)
, C line (λ=656.3nm), F line (λ=486.1nm)
．． nm), g-line (λ = 435.8 nm), and astigmatism (Ast), coma aberration (COma), and distortion aberration (Di s) when ray tracing calculations are performed from the 111- side. shown respectively. In addition, in order to explain the performance of the eyepiece lens in an easy-to-understand manner, in the aberration calculation,
The objective lens was made aberration-free.

From each aberration diagram above, each example is II! It is clear that the spherical aberration (ii) is sufficiently well corrected, and the curvature of field, coma aberration, and distortion are also well corrected, and in particular, the distortion is very well corrected with a factor of about 1.

(Effects of the Invention) As described above, according to the present invention, it is possible to easily manufacture a high-performance wide-field eyepiece with small distortion, good correction of spherical aberration of the pupil, and excellent flatness of the image plane. 1. An eyepiece lens suitable for inspecting flat regular fine patterns such as IC devices. Moreover, it becomes possible to supply it at low cost.

[Brief explanation of the drawing]

FIG. 1 is an optical path diagram of an eyepiece lens according to the present invention, and FIGS. 2 to 5 are aberration diagrams of first to fourth embodiments of the present invention. (Explanation of symbols of main parts) L, ...... Second lens L, ...... Second lens L, ...... Third lens L4・・・・・・Fourth lens applicant Takao Watanabe, agent of Nippon Kogaku Kogyo Co., Ltd.

Claims (1)

[Claims] In order from the light incident side, the first lens is a positive lens, the second lens is a biconcave negative lens, the third lens is a positive lens, and the third lens is a positive lens with a surface with a stronger curvature facing toward the incident light side. It has 4 lenses,
Let the overall focal length be 1-1, the focal lengths of the second lens and the fourth lens be fl, (,, the composite focal length of the first to third lenses be F', and the output light of the fourth lens be When the radius of curvature of the side lens is r, o, 5F < l fl l < o, aF (1) 0.9
F< L (i, 4F' (2) o, il"'< f,
<0.5F' (3)-〇, 7 <F/r, <0.7
A wide-field eyepiece that satisfies each condition (4).