JPH10142498A - Objective for ultraviolet ray - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the objective which has excellent transmissivity to short- wavelength ultraviolet rays and has various aberrations compensated excellently by including a cemented lens consisting of two quartz lenses across one fluorite lens. SOLUTION: This objective consists of a negative meniscus lens L1, L1, a biconcave lens L2, a 3-cemented lens L3 of a biconvex lens, a biconcave lens, and a biconvex lens, a 3-cemented lens L4 of a negative meniscus lens, a biconvex lens, and a negative meniscus lens, a 3-cemented lens L5 of a biconcave lens, biconvex lens, and a negative meniscus lens, a 3-cemented lens L6 of a biconvex lens, a biconcave lens, and a biconvex lens, and a 3-cemented lens L7 of a negative meniscus lens, a biconvex lens, and a biconcave lens. The 3-cemented lenses L3 to L7 have quartz lenses arranged on both sides and fluorite lenses arranged in the centers. Then surfaces of the quartz lenses which come into contact with gas or a vacuum are more than twice as many as surfaces of the fluorite lenses which come into contact with gas or a vacuum.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an objective lens for ultraviolet rays, and more particularly to an objective lens having a good transmittance for ultraviolet rays.

[0002]

2. Description of the Related Art A fisheye lens having a good transmittance for light rays in the visible region has been known.

[0003]

However, an objective lens such as a bright fisheye lens which has a good transmittance for ultraviolet light having a wavelength of about 300 nm (nanometer) or less and has a chromatic aberration corrected well is still available. unknown.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and has a good transmittance with respect to ultraviolet light having a wavelength of about 300 nm or less, and a bright ultraviolet light having various aberrations well corrected. It is an object of the present invention to provide an objective lens.

[0005]

According to the present invention, there is provided an ultraviolet objective lens comprising a quartz lens made of quartz and a fluorite lens made of fluorite. Including a cemented lens formed by bonding two quartz lenses sandwiching the fluorite lens, the number of surfaces of the quartz lens in contact with gas or vacuum is two times the number of surfaces of the fluorite lens in contact with gas or vacuum. Provided is an objective lens for ultraviolet light, characterized in that the objective lens is twice or more.

According to a preferred embodiment of the present invention, the number of three cemented lenses formed by bonding three lenses is at least half of the total number of lens components constituting the entire lens system.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The reason why a bright fisheye lens which has a good transmittance for ultraviolet rays having a wavelength of 300 nm or less and has well-corrected various aberrations has not yet been realized will be considered. Generally, not only fish-eye lenses but also lenses using ordinary optical glass materials cannot sufficiently transmit ultraviolet rays. In particular, it is no exaggeration to say that the transmittance of a normal lens system designed for visible light is almost zero for light in the ultraviolet region having a wavelength shorter than about 300 nanometers. This is due to the fact that the transmittance of most optical glass materials for the ultraviolet rays in this region is very small. This tendency is exacerbated as the size and complexity of the lens system increases.

Accordingly, the material used for the ultraviolet objective lens is a material having a good transmittance to ultraviolet light in this region, that is, synthetic quartz, fluorite, and other crystalline materials. At present, the materials used for UV objectives are substantially fluorite and synthetic quartz. These two types of optical materials both have a small refractive index and a dispersion ratio close to each other. For this reason, it is well known that a lens made of such an optical material often cannot obtain a required brightness if the achromatic condition is satisfied. Usually, the material having a large dispersion rate used for the positive lens is practically limited to fluorite. However, the lens made of fluorite has relatively poor smoothness of the polished surface, so that light having a short wavelength such as ultraviolet light tends to deteriorate the image contrast.

As described above, synthetic quartz, fluorite, and various crystalline materials are known as optical materials that transmit ultraviolet light well. However, fluorite and synthetic quartz are relatively readily available and physicochemically stable. Therefore, a lens system having good transmittance for ultraviolet rays can be obtained by using only these two types of materials. However, as mentioned above,
In these two types of materials, the refractive index and the dispersion are close to each other. Therefore, it is not easy to correct various aberrations such as chromatic aberration particularly in a bright lens system. These aberration difficulties increase more and more in a large-aperture wide-angle lens having a complicated lens system.

Therefore, in the present invention, more cemented lenses (hereinafter, simply referred to as "three cemented lenses") formed by bonding three lenses are arranged, the refractive power of each lens is reduced, and the radius of curvature is reduced. By making it larger, good aberration correction is performed for ultraviolet rays. With this configuration, the number of lenses increases,
In the present invention, the advantage in aberration correction is prioritized. Also,
In order to reduce the number of lens components constituting the lens system, it is more advantageous to configure the system with three cemented lens components than to configure the system with two cemented lens components.
In particular, in the present invention, it is desirable that the number of the three cemented lenses is at least half of the total number of lens components constituting the entire lens system.

Next, the advantage of reducing the number of lens components constituting the lens system will be described. It is well known that in a lens system, light reflected from a surface that comes into contact with a gas such as air or a vacuum becomes a flare and reduces the contrast of an image. Therefore, in order to prevent a decrease in image contrast, the smaller the number of lens components constituting the lens system, the better. In particular, the effect of the antireflection film is actually reduced for lenses made of an optical material having a low refractive index such as fluorite or quartz. Therefore, reducing the number of lens components is advantageous in improving image contrast.

Next, the arrangement order of the three cemented lenses in the ultraviolet objective lens of the present invention will be described. When a three-joint lens is formed by bonding three lenses, a lens made of fluorite (hereinafter, referred to as a “fluorite lens”) is disposed on both sides, and a lens made of quartz (hereinafter, referred to as a “quartz lens”) is provided at the center. ) May be placed. Conversely, a quartz lens may be arranged on both sides, and a fluorite lens may be arranged at the center. The present invention often employs a configuration in which quartz lenses are arranged on both sides and a fluorite lens is arranged in the center. Specifically, a configuration is employed in which the number of surfaces of the quartz lens that is in contact with a gas such as air or a vacuum is at least twice the number of surfaces of the fluorite lens that is in contact with a gas or a vacuum. Hereinafter, the reason why the above configuration is adopted will be described.

In general, the scattering of light passing through a surface having fine irregularities increases as the wavelength of light decreases. Therefore, the polished surface of the lens needs to have a smoothness about twice as large as that required for visible light for ultraviolet light having a wavelength of 300 nm or less. Fluorite is a soft material and has the fragility that crystal materials tend to have. Therefore, the polishing of the fluorite lens requires a high level of technology, and it is difficult to obtain a sufficiently smooth polished surface with no fine loss even if the polishing operation is performed with careful consideration. On the other hand, quartz is a hard material and easy to polish. Therefore, it is easy to obtain a smoother polished surface with a quartz lens than with a fluorite lens and also with a lens made of a general glass material. Therefore, for a lens having a surface that is in contact with a gas such as air or a vacuum, it is considered that it is easier to obtain a smoother surface with less scattering by using quartz than by fluorite.

Further, if the three-joint lens is configured such that the surface of the fluorite lens is in contact with the surface of the quartz lens without contacting a gas such as air or a vacuum, minute omissions on the surface of the fluorite lens can be removed with an adhesive. Filling can reduce the degree of scattering. Therefore, in the present invention, it is desirable to employ more triple junction lenses in which a fluorite lens is disposed at the center and quartz lenses are disposed on both sides thereof. in this case,
It is desirable to use an adhesive having a refractive index similar to that of fluorite. For the above reasons, the present invention includes a cemented lens formed by bonding one fluorite lens and two quartz lenses sandwiching the fluorite lens, and the surface of the quartz lens in contact with a gas such as air or vacuum. Is twice or more the number of surfaces of the fluorite lens in contact with a gas such as air or a vacuum.

A three-junction lens in which a fluorite lens is disposed on both sides and a quartz lens is disposed in the center can secure a relatively large radius of curvature, so that various aberrations such as chromatic aberration can be satisfactorily corrected. Is advantageous. However, in the present invention, in order to improve the contrast of an image that does not appear in the calculated value, a method disadvantageously used for correcting various aberrations such as chromatic aberration is dared to be adopted.

[0016]

Embodiments of the present invention will be described below with reference to the accompanying drawings. [First Embodiment] FIG. 1 is a diagram showing the configuration of an ultraviolet objective lens in the first embodiment. The ultraviolet objective lens of FIG. 1 includes, in order from the object side, a negative meniscus lens L1 having a convex surface facing the object side, a biconcave lens L2, a three-joint lens L3 of a biconvex lens, a biconcave lens, and a biconvex lens, and a convex surface on the object side. Cemented lens L consisting of a negative meniscus lens, a biconvex lens, and a negative meniscus lens with a concave surface facing the object side.
4. A three-junction lens L5 consisting of a biconcave lens, a biconvex lens and a negative meniscus lens having a concave surface facing the object side, a three-junction lens L6 consisting of a biconvex lens, a biconcave lens and a biconvex lens, and a negative meniscus lens having a convex surface facing the object side And a three-junction lens L7 of a biconvex lens and a biconcave lens, and a parallel plane plate.

The following Table (1) shows values of specifications of the ultraviolet objective lens in the first embodiment. In Table (1), f indicates the focal length, FNO indicates the F number, and 2α indicates the angle of view. The leftmost number indicates the order of each lens surface from the object side, r indicates the radius of curvature of each lens surface,
d is the distance between the lens surfaces, and n1 to n4 are each 2 wavelengths.
90 nm, 270 nm, 280 nm, and 300 nm
3 shows the refractive index of quartz and fluorite for the light of FIG.

[0018]

Table 1 f = 10.0 FNO = 1.2 2α = 120 ° rd 1 569.83927 2.00000 (quartz) 2 15.92105 12.80000 3 -45.81356 3.00000 (fluorite) 4 26.46235 6.00000 5 92.36426 12.90000 (quartz) 6 -24.58024 0.90000 (Fluorite) 7 19.52087 12.90000 (quartz) 8 -58.10353 7.00000 9 50.32944 1.00000 (quartz) 10 22.07030 17.00000 (fluorite) 11 -18.51688 1.00000 (quartz) 12 -50.32944 0.20000 13 -385.29474 1.00000 (quartz) 14 19.35234 15.00000 (fluorite) (Stone) 16 -18.49253 1.00000 (quartz) 17 -60.99457 0.10000 18 24.94629 10.00000 (fluorite) 19 -26.89408 1.00000 (quartz) 20 15.20151 8.00000 (fluorite) 21 -129.39174 0.10000 22 24.74891 0.80000 (quartz) 23 10.86282 10.00000 (fluorite) ) 24 -17.58380 0.70000 (quartz) 25 38.82218 5.00000 26 ∞ 2.00000 (quartz) 27 ∞ 3.32959 (refractive index of quartz and fluorite) n1 n2 n3 n4 quartz 1.490837 1.497945 1.494165 1.487836 fluorite 1.456054 1.460871 1.458316 1.454002

FIG. 2 is a diagram showing various aberrations in the first embodiment. In each aberration diagram, FNO represents an F number, α represents a half angle of view, 9 represents light having a wavelength of 290 nm, and 7 represents light having a wavelength of 270 nm.
nm, 8 indicates light having a wavelength of 280 nm, and 3 indicates light having a wavelength of 300 nm. In the aberration diagram showing astigmatism, a solid line indicates a sagittal image plane, and a broken line indicates a meridional image plane. As is clear from the aberration diagrams, in the present embodiment, various aberrations are favorably corrected for each ultraviolet ray of 300 nm or less.

[Second Embodiment] FIG. 3 is a view showing the arrangement of an ultraviolet objective lens in a second embodiment. The ultraviolet objective lens in FIG. 3 includes, in order from the object side, a two-joint lens L composed of a negative meniscus lens L1 having a convex surface facing the object side, and a biconcave lens and a negative meniscus lens having a convex surface facing the object side.
2. A three-junction lens L3 of a biconvex lens, a biconcave lens, and a biconvex lens, a three-junction lens L4 of a negative meniscus lens having a convex surface facing the object side, a biconvex lens, and a negative meniscus lens having a concave surface facing the object side, and a biconvex lens And a three-junction lens L5 of a biconcave lens and a biconvex lens, a three-junction lens L6 of a negative meniscus lens having a convex surface facing the object side, a biconvex lens, and a negative meniscus lens having a concave surface facing the object side, a biconvex lens and a biconcave lens , And a parallel plane plate.

Table 2 below summarizes the data values of the objective lens for ultraviolet rays in the second embodiment. In Table (2), f indicates the focal length, FNO indicates the F number, and 2α indicates the angle of view. The leftmost number indicates the order of each lens surface from the object side, r indicates the radius of curvature of each lens surface,
d is the distance between the lens surfaces, and n1 to n4 are each 2 wavelengths.
90 nm, 270 nm, 280 nm, and 300 nm
3 shows the refractive index of quartz and fluorite for the light of FIG.

[0022]

[Table 2] f = 10.0 FNO = 1.2 2α = 120 ° rd 1 246.24072 2.00000 (quartz) 2 14.44329 13.30000 3 -53.65620 2.00000 (fluorite) 4 12.82039 9.00000 (quartz) 5 17.77404 4.99381 6 65.70246 10.00000 ( (Quartz) 7 -76.83023 1.00000 (fluorite) 8 20.32579 13.00000 (quartz) 9 -23.48052 11.61276 10 796.91187 1.00000 (quartz) 11 17.30463 19.00000 (fluorite) 12 -16.50920 1.00000 (quartz) 13 -796.91187 0.20000 14 30.04393 11.00000 (fluorite) 15 -23.32835 1.00000 (quartz) 16 21.18617 9.00000 (fluorite) 17 -62.30187 0.10000 18 51.79865 1.00000 (quartz) 19 16.53140 15.00000 (fluorite) 20 -20.27813 1.00000 (quartz) 21 -1007.86000 0.10000 22 19.94192 10.00000 (fluorite) 23 -25.63788 1.00000 (quartz) 24 41.87310 5.00000 25 ∞ 2.00000 (quartz) 26 ∞ 3.52316 (refractive index of quartz and fluorite) n1 n2 n3 n4 quartz 1.490837 1.497945 1.494165 1.487836 fluorite 1.456054 1.460871 1.458316 1.454002

FIG. 4 is a diagram showing various aberrations in the second embodiment. In each aberration diagram, FNO represents an F number, α represents a half angle of view, 9 represents light having a wavelength of 290 nm, and 7 represents light having a wavelength of 270 nm.
nm, 8 indicates light having a wavelength of 280 nm, and 3 indicates light having a wavelength of 300 nm. In the aberration diagram showing astigmatism, a solid line indicates a sagittal image plane, and a broken line indicates a meridional image plane. As is clear from the aberration diagrams, in the present embodiment, various aberrations are favorably corrected for each ultraviolet ray of 300 nm or less.

As described above, in each embodiment, it is possible to achieve a fisheye lens for ultraviolet rays which has a bright F-number of 1.2 and an angle of view of 120 degrees. In the three cemented lenses L3 of the respective embodiments, the positive lens needs to have a larger dispersion than the negative lens. This is to correct the chromatic aberration generated in the negative meniscus lens L1, especially the chromatic aberration of magnification. In each of the three cemented lenses L4, L5, and L6 of each embodiment, the dispersion of the positive lens needs to be smaller than the dispersion of the negative lens. This is to correct various aberrations such as chromatic aberration.

[0025]

As described above, according to the present invention, it is possible to provide a bright ultraviolet objective lens which has a good transmittance for ultraviolet light having a wavelength of about 300 nm or less and has well-corrected various aberrations. Can be realized.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of an ultraviolet objective lens in a first embodiment.

FIG. 2 is a diagram illustrating various aberrations in the first example.

FIG. 3 is a diagram showing a configuration of an ultraviolet objective lens in a second embodiment.

FIG. 4 is a diagram illustrating various aberrations in the second example.

[Explanation of symbols]

 Li Each lens component

Claims (4)

[Claims] 1. An ultraviolet objective lens comprising a quartz lens made of quartz and a fluorite lens made of fluorite, wherein a joint is formed by bonding one fluorite lens and two quartz lenses sandwiching the fluorite lens. An ultraviolet objective lens including a lens, wherein the number of surfaces of the quartz lens that is in contact with gas or vacuum is at least twice the number of surfaces of the fluorite lens that is in contact with gas or vacuum. 2. The ultraviolet objective lens according to claim 1, wherein the number of three cemented lenses formed by bonding three lenses is at least half of the total number of lens components constituting the entire lens system. 3. A negative meniscus lens L1 having a convex surface facing the object side, a biconcave lens L2, a three-joint lens L3 comprising a biconvex lens, a biconcave lens and a biconvex lens, and a negative meniscus having a convex surface facing the object side in order from the object side. A three-junction lens L4 of a lens, a biconvex lens, and a negative meniscus lens having a concave surface facing the object side, a three-junction lens L5 of a biconcave lens, a biconvex lens, and a negative meniscus lens having a concave surface facing the object side, a biconvex lens and a biconcave lens 3. The ultraviolet light according to claim 1, further comprising a three-junction lens L <b> 6 including a negative meniscus lens having a convex surface facing the object side, and a three-junction lens L <b> 7 including a biconvex lens and a biconcave lens. Objective lens. 4. In order from the object side, a negative meniscus lens L1 having a convex surface facing the object side, a double junction lens L2 of a biconcave lens and a negative meniscus lens having a convex surface facing the object side, a biconvex lens, a biconcave lens and a biconvex lens And three junction lens L
3. A negative meniscus lens having a convex surface facing the object side, a biconvex lens, and a negative meniscus lens having a concave surface facing the object side.
A cemented lens L4, a triple cemented lens L5 of a biconvex lens, a biconcave lens, and a biconvex lens; a triple cemented lens L6 of a negative meniscus lens having a convex surface facing the object side, a biconvex lens, and a negative meniscus lens having a concave surface facing the object side; 3. The ultraviolet objective lens according to claim 1, further comprising a two cemented lens L <b> 7 including a biconvex lens and a biconcave lens. 4.