JP3346227B2 - Optical system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical system using an aberration correcting optical system, and can obtain high imaging performance over a wide field of view by correcting the aberration of the optical system.

[0002]

2. Description of the Related Art FIG. 6 shows the configuration of a large projection television. In the large projection television 4 as shown in FIG.
The light emitted from the illumination light source 5 and transmitted through the LCD 6
Irradiates the screen 8.
In order to obtain a bright image, the illumination light source 5 of the LCD 6 is required to illuminate the LCD 6 with high illuminance. At this time, if the illumination light source 5 has an aberration, blur occurs around the illumination range, and the illumination range is wider than the LCD 6. If the total amount of light emitted from the illumination light source 5 does not change, the illuminance of the LCD 6 decreases, and as a result, the brightness of the screen 8 of the large projection television 4 decreases.
Therefore, the illumination light source 5 needs to have a small aberration. However, the wavelength range of the light to be irradiated is wide, and it is difficult to realize the illumination light source 5 with a small aberration over a wide wavelength range, so that the illumination efficiency has been reduced.

There is a telescope as an application where a very small aberration is required in a wide field of view. In particular, there is a very high demand for large astronomical telescopes used for astronomy. FIG. 7 shows a configuration of a large reflecting telescope used in astronomy. In this case, it is necessary to achieve extremely low aberrations with a minimum lens configuration for structural reasons of being large. In general, a large telescope is provided with two reflecting mirrors, a primary mirror 9 and a secondary mirror 10, because the minimum aberration correction can be performed.

The most common telescope having two reflecting mirrors is a Cassegrain telescope in which the primary mirror 9 is a parabolic mirror and the secondary mirror 10 is a hyperboloid. This configuration has long been used in large telescopes. In recent years, a reflection telescope having a configuration called a Richey-Chretien type has come to be manufactured as a telescope which has been improved with respect to a field of view. In this reflection telescope, both the primary mirror 9 and the secondary mirror 10 have hyperboloidal surface shapes. Although the Richey-Chretien telescope has a drawback that the focal plane 11 warps, the spherical surface and coma aberration can be completely corrected, so that the Richey-Chretien telescope has a wider field of view than the Cassegrain telescope. Further, an example in which an elliptical surface is used for the primary mirror 9 can be seen.

In order to obtain a wider field of view in these telescopes, the focal position 12 of the primary mirror 9 is not used without using the secondary mirror 10.
(Hereinafter referred to as the primary focus). At this time, in the Cassegrain type in which the primary mirror shape is a paraboloid, the aberration largely depending on the viewing angle becomes very large except for a very small part of the center of the viewing field. When the primary mirror 9 using an ellipsoid or a hyperboloid is used, although the above-mentioned aberration depending on the viewing angle is relatively small, spherical aberration exists even at the center of the viewing field, and the image is blurred. For this reason, it is common to install an optical system called a main focus correction optical system 13 near the main focus 12 to perform aberration correction. Regarding the main focus correction optical system 13, "Characte
ristics of Three-Lens Corrector for the Primary For
cus of Large Telescopes ”, National Astronomical Observatory of Japan, Series 2, Vol. 20, No. 4 solves the positive, negative, and positive power arrangement as the main focus correction optical system 13 used for the ellipsoid, paraboloid, and hyperboloid. It is shown that there is.

FIG. 8 shows an example of a conventional main focus correcting optical system 13 in a Richy-Chretien telescope. This example is disclosed in JP-A-6-230274.
The lens data is shown in Numerical Example 1 below. In FIG. 8, light enters from the right side, and light reflected by the primary mirror 9 enters the primary focus correction optical system 13. In FIG. 8, the first lens 14, the second lens 15, the first atmospheric dispersion correction optical system 1
6, a second atmospheric dispersion correction optical system 17 and a third lens 18. Since the refractive index of the Earth's atmosphere varies with wavelength, light from celestial bodies enters from space and the angle of refraction in the atmosphere when passing through the atmosphere varies with wavelength,
If you force it, the object you want to observe will be observed at a different position for each wavelength, but it is called an atmospheric dispersion correction optical system16,
Reference numeral 17 is provided to correct the effect observed at a different position for each wavelength. FIG. 9 is a diagram showing aberration diagrams of the conventional main focus correction optical system shown in FIG. From the aberration diagram shown in FIG. 9, it can be seen that the aberration generated in the primary mirror 9 has been corrected very well. The first lens 14 and the second lens 15 are made of a material of nd (refractive index) = 1.52 and vd (dispersion) = 64.2, which are most often used in the crown system. Chromatic aberration is reduced by using a phosphate glass.

Numerical Embodiment 1

[0008]

[Table 1]

Numerical Embodiment 1 Aspheric coefficient of

[0010]

[Table 2]

[0011]

When the third lens is as far away from the focal plane as possible, the degree of dimensional freedom of the observation equipment mounted near the focal plane increases. However, when the third lens is moved away from the focal point, there is a problem that the imaging performance is reduced. In addition, there is a problem that it is difficult to select a glass material for performing chromatic aberration correction over a wide wavelength range.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide an optical system which satisfactorily corrects aberrations with a small number of optical elements.

[0013]

According to a first aspect of the present invention, there is provided an optical system comprising: converging means for outputting convergent light; and an aberration correcting optical system for correcting aberration of the convergent light outputted from the converging means. In the optical system, the aberration correction optical system includes a first lens using a material with a refractive index of 1.52 and a dispersion of 64.2, and a second lens using a material with 60 <dispersion <64. And a third lens using a material having a refractive index of 1.49 and a dispersion of 84.5, wherein the power of each lens is positive,
They are arranged in negative and positive order.

An optical system according to a second aspect of the present invention has a third lens using a material having a refractive index of 1.50 and a dispersion of 81.6.

An optical system according to a third aspect of the present invention includes a converging means having a condensing optical system for condensing light.

An optical system according to a fourth aspect of the present invention includes a converging means having a reflecting optical system for reflecting and condensing light.

An optical system according to a fifth aspect of the present invention has one reflecting optical system.

An optical system according to a sixth aspect of the present invention includes a reflecting optical system having a hyperboloidal surface shape.

An optical system according to a seventh aspect of the present invention includes a reflection optical system having a parabolic surface shape.

The optical system according to the invention of claim 8 is provided with a reflecting optical system having an elliptical surface shape.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiment 1 FIG. FIG. 1 is a diagram showing a configuration of an aberration correction optical system used in the optical system according to the first embodiment of the present invention. In FIG. 1, the right side is a main mirror side of a telescope as a converging means for outputting convergent light, from which light enters. The first lens 1, the second lens 2, and the third lens 3 are arranged in this order from the right side, and light is condensed at the main focus 12. Numerical example 2 below shows lens data of a telescope whose aberration has been corrected by the aberration correction optical system of the first embodiment. The primary mirror of the telescope is a hyperboloid, the aberration correction optical system is positive,
Negative and positive power arrangement. Then, as shown in Numerical Example 2 below, the first lens 1 has nd (refractive index) =
1.52, vd (dispersion) = 64.2, and the second lens 2
60 <vd (dispersion) <64, and the third lens 3 uses a material with nd (refractive index) = 1.49 and vd (dispersion) = 84.5.

FIG. 2 shows an aberration diagram of the telescope whose aberration has been corrected by the aberration correcting optical system according to the first embodiment. D (thickness) of Embodiment 1 shown in Numerical Example 2 and Numerical Example 1
Comparing with d (thickness) of the conventional example as shown in the above, the image forming apparatus according to the first embodiment has the same imaging performance as the conventional example, smaller dimensions, and a dimensional margin near the focal point is secured. I understand.

As described above, according to the first embodiment, in the telescope having the primary mirror and the secondary mirror, by using the aberration correction optical system of the first embodiment instead of the secondary mirror, the number of optical elements can be reduced. Aberration correction can be satisfactorily corrected.
In the first embodiment, the main mirror of the telescope is shown as the converging means. However, the converging means may be a condensing optical system that condenses light, or reflects and condenses light. It may be a reflection optical system.

Numerical Embodiment 2

[0025]

[Table 3]

Numerical Embodiment 2 Aspheric coefficient of

[0027]

[Table 4]

Embodiment 2 Numerical data example 3 below shows lens data of a telescope whose aberration has been corrected by the aberration correcting optical system according to the second embodiment. Since the configuration of the aberration correction optical system according to the second embodiment is almost the same as that of the first embodiment, the configuration diagram including the following embodiments is omitted. In the second embodiment, as in the first embodiment, the primary mirror of the telescope has a hyperboloid, the aberration correction optical system has a positive, negative, and positive power arrangement. Uses the same glass material,
The third lens 3 uses a material having nd (refractive index) = 1.50 and vd (dispersion) = 81.6. FIG. 3 shows an aberration diagram of the telescope whose aberration has been corrected by the aberration correction optical system according to the second embodiment. Similar to the first embodiment, the second embodiment shown in Numerical Example 3 has the same imaging performance and smaller dimensions than the conventional example, and also has a sufficient dimensional margin near the focal point. You can see that it is.

Numerical Embodiment 3

[0030]

[Table 5]

Numerical Embodiment 3 Aspheric coefficient of

[0032]

[Table 6]

Embodiment 3 Numerical example 4 below shows lens data of the telescope whose aberration has been corrected by the aberration correction optical system of the third embodiment. In the third embodiment, the main mirror of the telescope is a paraboloid, the power arrangement of the aberration correction optical system is positive, negative, and positive, as in the first embodiment, and the glass material is the same as that of the first embodiment. Glass material is used. FIG. 4 shows an aberration diagram of the telescope whose aberration has been corrected by the aberration correcting optical system according to the third embodiment. In the third embodiment shown in Numerical Example 4,
It can be seen that the imaging performance is the same as the conventional example, the dimensions are small, and the dimensional margin near the focal point is secured. Further, as is apparent from Embodiment 2, the glass material of the third lens is nd
It is clear that the same effect can be obtained even when (refractive index) = 1.50 and vd (dispersion) = 81.6.

Numerical Embodiment 4

[0035]

[Table 7]

Numerical Embodiment 4 Aspheric coefficient of

[0037]

[Table 8]

Embodiment 4 FIG. The following numerical example 5 shows lens data of a telescope whose aberration has been corrected by the aberration correcting optical system of the fourth embodiment. In the fourth embodiment, the main mirror of the telescope has an elliptical surface, the power arrangement of the aberration correction optical system is positive, negative, and positive, as in the first embodiment, and the glass material is the same as that of the first embodiment. Is used. FIG. 5 shows an aberration diagram of the telescope whose aberration has been corrected by the aberration correction optical system according to the fourth embodiment. In the fourth embodiment shown in Numerical Example 5,
It can be seen that the imaging performance is the same as the conventional example, the dimensions are small, and the dimensional margin near the focal point is secured. Similarly to Embodiment 3, it is apparent that the same effect can be obtained even when the glass material of the third lens is nd (refractive index) = 1.50 and vd (dispersion) = 81.6.

Numerical Embodiment 5

[Table 9]

Numerical Embodiment 5 Aspheric coefficient of

[0041]

[Table 10]

[0042]

As described above, according to the present invention, it is possible to obtain an optical system in which aberration correction is properly corrected with a small number of optical elements.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a configuration of an aberration correction optical system used in an optical system according to a first embodiment of the present invention.

FIG. 2 is a diagram showing an aberration diagram of an aberration correction optical system used in the optical system according to the first embodiment of the present invention.

FIG. 3 is a diagram showing an aberration diagram of an aberration correction optical system used in an optical system according to a second embodiment of the present invention.

FIG. 4 is a diagram showing an aberration diagram of an aberration correcting optical system used in an optical system according to Embodiment 3 of the present invention.

FIG. 5 is a diagram showing an aberration diagram of an aberration correction optical system used in an optical system according to Embodiment 4 of the present invention.

FIG. 6 is a diagram showing a configuration of a conventional large projection television.

FIG. 7 is a diagram showing a configuration of a conventional large telescope.

FIG. 8 is a diagram showing a configuration of a conventional main focus correction optical system.

FIG. 9 is an aberration diagram of a conventional main focus correction optical system.

[Explanation of symbols]

1 First lens, 2nd lens, 3rd lens, 4
Large projection TV, 5 light source for illumination, 6 LCD, 7
Lens, 8 screen, 9 primary mirror, 10 secondary mirror, 11
Focal plane, 12 primary focus, 13 primary focus correction optical system, 1
4 First lens, 15 Second lens, 16 First atmospheric dispersion correction optical system, 17 Second atmospheric dispersion correction optical system, 18
Third lens.

Claims (8)

(57) [Claims] 1. An optical system comprising: converging means for outputting convergent light; and an aberration correcting optical system for correcting aberrations of the convergent light output from the converging means, wherein the aberration correcting optical system has a refractive index. 1.52, a first lens using a material with a dispersion of 64.2, a second lens using a material with 60 <dispersion <64, and a refractive index of 1.49 and a dispersion of 84.5. An optical system, comprising: a third lens made of the material described in (1), wherein the power of each lens is arranged in the order of positive, negative, and positive. 2. The third lens has a refractive index of 1.50.
The optical system according to claim 1, wherein a material having a dispersion of 81.6 is used. 3. An optical system according to claim 1, wherein said converging means has a light condensing optical system for condensing light. 4. The optical system according to claim 1, wherein said converging means has a reflection optical system for reflecting and condensing light. 5. The optical system according to claim 4, wherein the number of the reflecting optical system is one. 6. The optical system according to claim 4, wherein said reflection optical system has a hyperboloidal surface shape. 7. The optical system according to claim 4, wherein said reflection optical system has a parabolic surface shape. 8. The optical system according to claim 4, wherein said reflection optical system has an elliptical surface shape.