JP3430738B2 - Symmetric telecentric optics - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a symmetric type telecentric optical system, and more particularly, to both sides used in a relay system of an optical instrument, a measuring instrument requiring dimensional accuracy, an optical system for transferring a fine pattern, and the like. Telecentric unity magnification lens.

[0002]

2. Description of the Related Art There are many so-called equal-magnification lenses of Gauss type or modified Gauss type that form a finite object at an equal magnification. However, in this type of conventional equal-magnification lens, the off-axis chief ray has a certain inclination θ with respect to the optical axis.
Most of them are incident with. Therefore, even if the bignetting is zero, co
The image plane illumination decreases in proportion to s ⁴ θ. As a result, an illuminance difference occurs between the center of the screen and the periphery of the screen, which makes it impossible to accurately transfer a fine pattern, for example.

Generally, in the design of a symmetric unity-magnification lens, the position of the aperture stop is the entrance pupil, and aberration correction is performed in the lens group, that is, the rear group, arranged behind (on the image side of) the pupil. In this case, lateral aberrations (asymmetrical aberrations) such as coma, chromatic aberration of magnification, and distortion are eventually removed by making the optical system symmetrical. However, spherical aberration,
Longitudinal aberrations (symmetrical aberrations) such as astigmatism and axial chromatic aberration are quantitatively doubled and remain by making the optical system symmetrical. That is, the problem of aberration correction of the entire system results in correction of longitudinal aberration in the rear group.

In order to make the optical system telecentric, a ray having a certain inclination θ must be incident from the entrance pupil position and converted into a ray parallel to the optical axis by the rearmost lens. In the double-sided telecentric optical system, the magnification does not change much even if the object distance is slightly changed.

[0005]

As described above, in the conventional Gauss type or modified Gauss type equal-magnification lens, the off-axis chief ray enters and exits with a certain inclination with respect to the optical axis.
Even if the bignetting is zero, there is an inconvenience that an illuminance difference occurs between the center of the screen and the periphery of the screen. Further, when a conventional equal-magnification lens is used as a symmetrical and telecentric optical system, it is difficult to sufficiently correct so-called longitudinal aberration in the rear group.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a symmetrical telecentric optical system having good imaging performance while maintaining telecentricity on both sides.

[0007]

In order to solve the above-mentioned problems, the present invention comprises a front group GF and a rear group GR which are symmetrically arranged with respect to an aperture stop.
From the object side, in order from the object side, the positive lens L1 with the surface having the smaller absolute value of the radius of curvature facing the aperture stop side, the positive lens L2 having the surface with the larger absolute value of the radius of curvature facing the aperture stop side, and the aperture The rear lens group GR includes, in order from the aperture stop side, a negative lens L4 having a concave face toward the aperture stop side and an absolute value of the radius of curvature toward the aperture stop side. A positive lens L5 having a larger surface facing the positive lens L5 having a surface having a smaller absolute value of the radius of curvature toward the aperture stop side.
And a focal length of the front lens group GF is F, and a distance along the optical axis between the object-side surface of the positive lens L1 of the front lens group GF and the aperture stop. Is D, and the positive lens L1 and the positive lens L2
And an axial air distance between the positive lens L2 and the negative lens L3 is d4, and an axial air distance between the negative lens L3 and the aperture stop is d2. Provided is an optical system characterized by satisfying the condition of 1 <D / F d4 <d7 <d2 when d7.

According to a preferred aspect of the present invention, the positive lens L2 and the negative lens L3 of the front group GF and the rear group G are used.
The negative lens L4 and the positive lens L5 of R are integrally moved, or the positive lens L2 of the front group GF and the positive lens L5 of the rear group GR, and the negative lens L3 and the rear group of the front group GF. The negative lens L4 of the GR is moved integrally with each other to change the magnification.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION As described above, the symmetrical telecentric optical system of the present invention comprises the front group GF and the rear group GR which are symmetrically arranged with respect to the aperture stop. The front group GF has, in order from the object side, a positive lens L1 having a surface having a smaller absolute value of the radius of curvature facing the aperture stop side, and a positive lens having a surface having a larger absolute value of the curvature radius facing the aperture stop side. A lens L2 and a negative lens L3 having a concave surface facing the aperture stop side are provided. The rear group GF includes, in order from the aperture stop side, a negative lens L4 having a concave surface facing the aperture stop side, a positive lens L5 having a surface having the larger absolute value of the radius of curvature toward the aperture stop side, and an aperture stop. And a positive lens L6 with the surface having the smaller absolute value of the radius of curvature facing the side. As described above, the optical system of the present invention is symmetrical with respect to the aperture stop S arranged in the center, but for convenience, the front group GF and the rear group GR are arranged in order from the object side.

In the present invention, the following conditional expressions (1) and (2) are satisfied in order to secure the telecentricity and to obtain good image forming performance in the above-mentioned symmetrical lens structure. 1 <D / F (1) d4 <d7 <d2 (2)

Where F: focal length of the front lens group GF: distance along the optical axis between the object-side surface of the positive lens L1 and the aperture stop d2: between the positive lens L1 and the positive lens L2 On-axis air distance d4: On-axis air distance between positive lens L2 and negative lens L3 d7: On-axis air distance between negative lens L3 and aperture stop

Conditional expressions (1) and (2) are expressed by the front group G
Although only F is shown, it goes without saying that the rear group also satisfies the conditions corresponding to the conditional expressions (1) and (2) due to the symmetry of the optical system of the present invention. In the lens configuration described above, in order to convert a divergent ray having a certain inclination into a ray parallel to the optical axis by the rearmost lens L6, the lens system itself must be enlarged to some extent. Conditional expression (1) is a condition set based on this viewpoint. If the conditional expression (1) is not satisfied, it becomes difficult to secure the telecentricity, which is not preferable.

Conditional expression (2) is a condition regarding the arrangement of each lens. In order to satisfy the conditional expression (2), the front group GF
By arranging each lens of the rear group GR, it is possible to favorably correct longitudinal aberration, especially astigmatism, while maintaining telecentricity. The axial chromatic aberration and Petzval sum can be corrected by appropriately selecting the glass material of each lens.

As described above, in the both-side telecentric optical system, the magnification does not change much even if the object distance is changed to some extent. However, in the symmetrical telecentric unity magnification optical system of the present invention, the following two variable magnification methods are possible. In the first variable magnification method, the lenses L1 and L6 are
Is fixed, and the lenses L2 to L5 are integrally moved along the optical axis to change the magnification. In the second scaling method,
Lenses L1 and L6 are fixed, and lenses L2 and L6
5 and the lenses L3 and L4 are integrally moved along the optical axis to change the magnification.

As shown in the embodiments described later, the second variable magnification method is effective in correcting coma aberration that occurs during variable magnification.
Further, the optical system of the present invention substantially retains the telecentricity on both sides regardless of which variable magnification method is adopted.

[0016]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a diagram showing the configuration of a symmetrical telecentric optical system according to an embodiment of the present invention. The illustrated optical system is composed of two lens groups, that is, a front group GF and a rear group GR, which are symmetrically arranged with an aperture stop S interposed therebetween. Although the optical system shown in the drawing is symmetrical, the front lens group G is a lens group disposed on the object side of the aperture stop S (on the left side in the figure).
This embodiment will be described assuming that the lens unit F is F, and the lens unit disposed on the image side (the emission side on the right side in the drawing) is the rear unit GR.

The optical system of FIG. 1 has a positive meniscus lens L1 having, in order from the object side, a meniscus shape having a concave surface facing the object side, and a surface having the smaller absolute value of the radius of curvature facing the aperture stop S side. , A positive meniscus lens L2 having a meniscus shape having a convex surface facing the object side and having a surface having a larger absolute value of the radius of curvature facing the aperture stop S side, and a cemented negative cemented with a biconvex lens and a biconcave lens. A lens L3, an aperture stop S, a cemented negative lens L4 formed by laminating a biconcave lens and a biconvex lens, a meniscus shape having a convex surface facing the image side, and a large absolute value of the radius of curvature on the aperture stop S side. A positive meniscus lens L5 having one surface facing the other side, and a positive meniscus lens L6 having a meniscus shape having a concave surface facing the image side and having the surface having the smaller absolute value of the radius of curvature toward the aperture stop S side. ing

In this embodiment, the lenses L1 and L6 are fixed and the lenses L2 to L5 are integrally moved along the optical axis to change the magnification according to the first variable magnification method. FIGS. 2 and 3 show a state in which the zooming is performed on the enlargement side and the reduction side according to the first scaling method, respectively. Further, according to the second variable magnification method, the lenses L1 and L6 are fixed and the lens L
2 and L5 and the lenses L3 and L4 are integrally moved along the optical axis to change the magnification. FIGS. 4 and 5 show a state in which the zooming is performed on the enlargement side and the reduction side according to the second scaling method, respectively.

The following table (1) lists the values of the specifications of this embodiment. In Table (1), β is the imaging magnification and NA is the numerical aperture. The leftmost number is the order of the lens surfaces from the object side, r is the radius of curvature of each lens surface, d is the distance between the lens surfaces, and nd and νd are d lines (λ = 587.
The refractive index and the Abbe number for 56 nm are shown.

[0020]

[Table 1]   β = -1.00   NA = 0.178   Object distance = 89.9   Image point distance = 89.9             rd nd νd    1 -990.8415 12.000 1.74810 52.30    2 -128.0000 38.500    3 88.6000 17.000 1.71300 53.93    4 827.5000 8.5000    5 45.0000 23.000 1.67025 57.53    6 -160.0000 5.600 1.67270 32.17    7 25.8400 17.620    8 ∞ 17.620 (aperture stop S)    9 -25.8400 5.600 1.67270 32.17   10 160.0000 23.000 1.67025 57.53   11 -45.0000 8.5000   12 -827.5000 17.000 1.71300 53.93   13 -88.6000 38.500   14 128.0000 12.000 1.74810 52.30   15 990.8415 89.900 (Variable spacing during scaling)                   First scaling method Second scaling method               Expansion side Reduction side Expansion side Reduction side β 1.05 0.95 1.1 0.9 Object distance 89.9 89.9 89.9 89.9 Image point distance 90.02 90.01 90.36 90.35 d2 29.2 48.0 22.4 56.0 d4 (invariant) (invariant) 9.8 7.09 d11 (invariant) (invariant) 7.2 9.91 d13 47.8 29.0 54.6 21.0 (Value corresponding to the condition)   F = 73.8 (1) D / F = 1.656 (2) d2 = 38.5, d4 = 8.5, d7 = 17.62 Therefore, d4 <d7 <d2 is satisfied.

FIG. 6 is a diagram showing various aberrations of the unit magnification optical system symmetrically arranged as shown in FIG. 7 and 8 are various aberration diagrams in a state where they are arranged so as to be magnified toward the enlargement side and the reduction side, respectively, according to the first variable magnification method. 9 and 10 are graphs showing various aberrations in a state in which they are arranged so as to be magnified toward the enlargement side and the reduction side, respectively, according to the second magnification system. In each aberration diagram, NA indicates the numerical aperture and Y indicates the image height.
Further, in the aberration diagram showing astigmatism, the solid line shows the sagittal image plane and the broken line shows the meridional image plane.

As is clear from each aberration diagram, it is understood that various aberrations are properly corrected in this embodiment, including during zooming. In particular, the second variable magnification method, in which the lenses L1 and L6 are fixed and the lenses L2 and L5 and the lenses L3 and L4 are integrally moved along the optical axis to change the magnification, occurs during magnification change. It can be seen that it is effective in correcting coma aberration. In addition, the second variable magnification method performs variable magnification in the range of magnification β = 1.1 to 0.9, and in this range, the inclination of the chief ray on the object side and the image side is 2
It is about 0 ', and it can be seen that both sides are telecentric.

[0023]

As described above, according to the present invention, it is possible to realize a unit-magnification optical system having good imaging performance while maintaining telecentricity on both sides. Further, by adopting the above-described variable magnification method, it is possible to perform variable magnification in a good image formation state while substantially maintaining the both-side telecentricity.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a symmetrical telecentric optical system according to an example of the present invention.

FIG. 2 is a diagram showing a state in which the zoom lens is arranged so as to be magnified toward an enlargement side according to a first scaling method.

FIG. 3 is a diagram showing a state in which the zoom lens is arranged so as to be scaled to a reduction side according to a first scaling method.

FIG. 4 is a diagram showing a state in which the zoom lens is arranged so as to be magnified toward the enlargement side according to a second scaling method.

FIG. 5 is a diagram showing a state in which the zoom lens is arranged so as to be zoomed toward a reduction side according to a second scaling method.

FIG. 6 is a diagram of various types of aberration of the symmetrically arranged unity magnification optical system in FIG. 1;

FIG. 7 is a diagram of various types of aberration in a state in which the zoom lens is arranged so as to be zoomed toward the enlargement side according to the first zooming method.

FIG. 8 is a diagram of various types of aberration in a state in which the zoom lens is arranged so as to be zoomed toward the reduction side according to the first zooming method.

FIG. 9 is a diagram of various types of aberration in a state in which the zoom lens is arranged so as to be zoomed toward the enlargement side according to the second zooming method.

FIG. 10 is a diagram of various types of aberration in a state in which the zoom lens is arranged so as to be zoomed toward the reduction side according to the second zooming method.

[Explanation of symbols]

GF front group GR after group L lens component S aperture stop

─────────────────────────────────────────────────── ─── Continuation of front page (56) References JP-A-4-333814 (JP, A) JP-A-4-42208 (JP, A) JP-A 63-316817 (JP, A) JP-A 53- 60655 (JP, A) JP-A-8-15609 (JP, A) JP-A 64-19317 (JP, A) JP-B 42-704 (JP, B1) JP-B 57-13849 (JP, B1) (58) Fields investigated (Int.Cl. ⁷ , DB name) G02B 9/00-17/08 G02B 21/02-21/04 G02B 25/00-25/04

Claims (3)

(57) [Claims] 1. A front lens group GF and a rear lens group GR which are arranged symmetrically with respect to an aperture stop. The front lens group GF has a surface having a smaller absolute value of a radius of curvature on the aperture stop side in order from the object side. Positive lens L1 directed toward the aperture stop, a positive lens L2 directed toward the aperture stop side having the larger absolute value of the radius of curvature, and a negative lens L3 directed toward the aperture stop side with a concave surface.
The rear group GR includes, in order from the aperture stop side, a negative lens L4 having a concave surface facing the aperture stop side and a positive lens L5 having a surface having a larger absolute value of the radius of curvature toward the aperture stop side. And a positive lens L6 having a positive lens L6 with the surface having the smaller absolute value of the radius of curvature facing the aperture stop side. In the telecentric unity magnification optical system, the focal length of the front group GF is F, and The distance along the optical axis between the object side surface of the lens L1 and the aperture stop is D, and the positive lens L1 and the positive lens L
The axial air distance between the positive lens L2 and the positive lens L2 is
And the axial air gap between the negative lens L3 and the negative lens L3 is d4,
An optical system which satisfies a condition of 1 <D / F d4 <d7 <d2, where d7 is an axial air distance between the negative lens L3 and the aperture stop. 2. The variable magnification is performed by integrally moving the positive lens L2 and the negative lens L3 of the front group GF and the negative lens L4 and the positive lens L5 of the rear group GR. 1. The optical system according to 1. 3. The positive lens L2 of the front group GF, the positive lens L5 of the rear group GR, and the negative lens L of the front group GF.
3. The optical system according to claim 1, wherein the third lens unit 3 and the negative lens L4 of the rear group GR are integrally moved to perform zooming.