Four-piece wide-band achromatic apochromatic refractive telescope optical system

Abstract

The application discloses a four-piece wide-band achromatic apochromatic refractive telescope optical system, which is composed of three spherical lenses and one aspherical lens. The optical system is sequentially provided with a spherical double-convex lens A, a spherical double-convex lens B, a spherical double-concave lens C and an aspherical double-convex lens D along the light path direction. The optical system realizes high correction of spherical aberration, axial chromatic aberration, sagittal chromatic aberration, coma and high-order aberration in a wide-band range from i line of ultraviolet 365nm wavelength to t line of near-infrared 1014nm wavelength, and has the advantages of less lens quantity, small interval, simple structure, low cost, light weight, compact size and the like. The on-axis Strehl Ratio in the 365nm-1014nm wavelength range is greater than 99% at the focal point position of e line of 546nm wavelength. The application is suitable for imaging and visual observation.

Description

Technical Field

[0001] This invention relates to optical systems for astronomical optical telescopes, specifically to a simple and compact four-element wide-band achromatic, spherical, and coma-correcting refracting telescope optical system. Background Technology

[0002] For decades, the correction range of apochromatic refractors has been largely limited to the range from the g-line (436 nm) to the r-line (707 nm), failing to fully cover the human eye's photosensitive wavelength range of 380 nm–780 nm, and also unable to provide adequate correction for the near-infrared band, which is crucial in astronomy. To broaden the operating wavelength of the refraction system, a larger number of lens structures are often required, which not only increases manufacturing difficulty and cost but also increases the system's size and weight. The increased surface area also increases stray light scattering, reducing the system's transmittance and image contrast. Summary of the Invention

[0003] Purpose of the invention: In view of the above problems, the present invention provides a simple and compact four-element wide-band achromatic, spherical, and coma-correcting refracting telescope optical system.

[0004] This invention is implemented using the following scheme:

[0005] The optical system of a four-element wideband achromatic, spherical, and coma-correcting refracting telescope consists of three spherical lenses and one aspherical lens. Along the optical path, the system includes a spherical biconvex lens A, a spherical biconvex lens B, a spherical biconcave lens C, and an aspherical biconvex lens D. This optical system provides high-level correction for spherical aberration, axial chromatic aberration, transverse chromatic aberration, coma, and higher-order aberrations across a wide wavelength range from the i-line (365nm ultraviolet) to the t-line (1014nm near-infrared). The maximum focal offset of the optical system is less than ±0.00035%. At the focal position of the e-line (546nm wavelength), where the human eye is most sensitive, the Steller ratio is greater than 99% within the 365nm–1014nm wavelength range. The optical glass used for the four lenses has an internal transmittance of greater than 95% within 10mm within the 365nm–1014nm wavelength range.

[0006] Furthermore, the spherical biconvex lens A is made of HOYA FCD100, the spherical biconvex lens B is made of SCHOTTF5, the spherical biconcave lens C is made of OHARA S-LAH97, and the aspherical biconvex lens D is made of HOYA M-FCD1.

[0007] Furthermore, the aspherical biconvex lens D has a front surface that is a quadratic aspherical with a conic coefficient k = -0.650, and a rear surface that is spherical.

[0008] Furthermore, the air gap between the spherical biconvex lens A and the spherical biconvex lens B is 0.35 mm, the air gap between the spherical biconvex lens B and the spherical biconcave lens C is 1.30 mm, and the air gap between the spherical biconcave lens C and the aspherical biconvex lens D is 1.40 mm.

[0009] Furthermore, the spherical biconvex lens A has a front surface vertex radius of curvature of 769.440 mm and a rear surface vertex radius of curvature of -1024.450 mm; the spherical biconvex lens B has a front surface vertex radius of curvature of 5448.830 mm and a rear surface vertex radius of curvature of -2264.190 mm; the spherical biconcave lens C has a front surface vertex radius of curvature of -1173.420 mm and a rear surface vertex radius of curvature of 539.960 mm; and the aspherical biconvex lens D has a front surface vertex radius of curvature of 403.760 mm and a rear surface vertex radius of curvature of -1829.030 mm.

[0010] Furthermore, the thickness of the spherical biconvex lens A is 14.50 mm; the thickness of the spherical biconvex lens B is 7.20 mm; the thickness of the spherical biconcave lens C is 5.00 mm; and the thickness of the aspherical biconvex lens D is 16.80 mm.

[0011] Compared with the prior art, the present invention has the following beneficial effects:

[0012] This invention presents a four-element wide-band achromatic, spherical, and coma-correcting refracting telescope system. Utilizing four lenses, each containing an aspherical surface, it achieves high-level correction of spherical aberration, axial chromatic aberration, transverse chromatic aberration, coma, and higher-order aberrations across a wide wavelength range, from the i-line at 365 nm in the ultraviolet to the t-line at 1014 nm in the near-infrared. Thus, the correction band of the apochromatic refractor not only completely covers the range of light sensitivity of the human eye (380 nm–780 nm) but also fully covers the range of light sensitivity of modern astronomical CCD and CMOS sensors. The maximum focus shift within the 365 nm–1014 nm wavelength range is less than ±0.00035%. At the focal position of the e-line at 546 nm, where the human eye is most sensitive, the Strehl ratio is greater than 99% within the 365 nm–1014 nm wavelength range. The Strehl ratio is the ratio of the light intensity between the image formed by an actual optical system (with aberrations) and the ideal Gaussian image point of an ideal perfect optical system (without aberrations) at the same aperture diameter. A Strehl ratio of 100% signifies that the optical system is perfectly aberration-free. Common industry practice considers an optical system to reach the "diffraction limit" and possess excellent optical performance when the Strehl ratio reaches 80%. The optical performance of this invention far exceeds the 80% Strehl ratio standard, and its performance is very close to that of an aberration-free optical system. Generally, achieving such optical performance requires a large number of lenses to correct aberrations, resulting in high cost, difficult manufacturing, and large size and weight. This invention uses only four lenses, resulting in a smaller number of lenses, smaller spacing, simpler structure, lower cost, lighter weight, and more compact size. The optical glass material used in this invention has been carefully selected and has high transmittance (greater than 95% transmittance within 10mm) in the wavelength range of 365nm–1014nm.

[0013] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below through specific embodiments and related drawings. Attached Figure Description

[0014] Figure 1 This is a structural diagram of the optical system in an embodiment of the present invention.

[0015] Figure 2 The diagram shows the chromatic aberration curve and the vertical chromatic aberration curve according to an embodiment of the present invention.

[0016] Figure 3 This is a graph showing the Strehl ratio versus wavelength (focus position of the e-line at 546 nm wavelength) according to an embodiment of the present invention.

[0017] Figure 4This is a diagram illustrating the image quality of the optical system according to an embodiment of the present invention (on-axis dot plot).

[0018] Figure 5 This is a diagram (matrix dot plot) illustrating the image quality of the optical system according to an embodiment of the present invention.

[0019] Figure 6 This is a graph showing the change of focal position with wavelength in an embodiment of the present invention.

[0020] The markings in the diagram are: 1-Spherical biconvex lens A, 2-Spherical biconvex lens B, 3-Spherical biconcave lens C, 4-Aspherical biconvex lens D. Detailed Implementation

[0021] This embodiment provides a simple and compact four-element broadband achromatic, spherical, and coma-correcting refracting telescope optical system. The optical system structure diagram is shown below. Figure 1 The system consists of three spherical lenses and one aspherical lens. Along the optical path, the optical system is arranged with a spherical biconvex lens A1, a spherical biconvex lens B2, a spherical biconcave lens C3, and an aspherical biconvex lens D4 in sequence. It features a small number of lenses, small spacing, simple structure, low cost, light weight, and compact size.

[0022] In this embodiment, the air gap between the spherical biconvex lens A and the spherical biconvex lens B is 0.35 mm, the air gap between the spherical biconvex lens B and the spherical biconcave lens C is 1.30 mm, and the air gap between the spherical biconcave lens C and the aspherical biconvex lens D is 1.40 mm.

[0023] The physical parameters of each lens are shown below:

[0024]

[0025]

[0026] The chromatic aberration curve and the vertical chromatic aberration curve in this embodiment are as follows: Figure 2 , Figure 2 Nine characteristic spectral lines in the 365nm-1014nm wavelength range were selected to plot chromatic aberration and transverse chromatic aberration curves. Figure 2 As can be seen in this embodiment, the residuals of spherical aberration, axial chromatic aberration, and transverse chromatic aberration are extremely small across a wide band, from the i-line with a wavelength of 365nm in the ultraviolet region to the t-line with a wavelength of 1014nm in the near-infrared region, achieving very good aberration correction.

[0027] The optical system composed of the above lenses achieves the following optical properties:

[0028] 1. Diameter: D = 150 mm;

[0029] 2. Focal length: f′=1200mm;

[0030] 3. Relative aperture: D / F = 1 / 8;

[0031] 4. Design wavelength: 365nm–1014nm;

[0032] 5. Strilll ratio: greater than 99% (365nm–1014nm, at the focal point of the e-line), such as... Figure 3 As shown;

[0033] 6. Maximum focus shift: less than ±0.00035% (365nm–1014nm); the focus position variation curve with wavelength is shown below. Figure 6 As shown;

[0034] 7. Radius of the dot plot: RMS radius 0.3μm (on the axis);

[0035] 8. Material internal transmittance within 10mm: greater than 95%;

[0036] The advantages of the simple and compact four-element wide-band achromatic, spherical, and coma-correcting refracting telescope optical system of this invention include:

[0037] (1) High correction of spherical aberration, axial chromatic aberration, transverse chromatic aberration, coma and higher-order aberrations in a wide band from the i-line of 365nm wavelength in the ultraviolet to the t-line of 1014nm wavelength in the near infrared.

[0038] (2) At the foci of the 546nm e-line, the Stryer ratio is greater than 99% in the range of 365nm–1014nm.

[0039] (3) It not only completely covers the light-sensitive band of the human eye, but also fully covers the light-sensitive band of modern astronomical COMS / CCD sensors.

[0040] (4) No infrared / ultraviolet cutoff filter is required. It can image the UBVRI band of modern astronomical photometry and obtain information on the ultraviolet and near-infrared bands of celestial bodies.

[0041] (5) The carefully selected glass material has high transmittance in the range of 365nm–1014nm (transmittance within 10mm is greater than 95%).

[0042] (6) The number of lenses is small, the spacing is small, the structure is simple, the cost is low, the weight is light, and the size is compact.

[0043] In summary, the four-element wide-band achromatic, spherical, and coma-correcting refracting telescope optical system of this invention consists of a spherical biconvex lens A, a spherical biconvex lens B, a spherical biconcave lens C, and an aspherical biconvex lens D. It features a small number of lenses, small spacing, simple structure, low cost, light weight, and compact size. By using four lenses made of high-transmittance glass material and employing a secondary aspherical element in the system, it achieves high-level correction of spherical aberration, axial chromatic aberration, transverse chromatic aberration, coma, and higher-order aberrations across a wide wavelength range from the i-line (365 nm ultraviolet) to the t-line (1014 nm near-infrared). It not only completely covers the human eye's light-sensitive range (380 nm–780 nm) but also fully covers the light-sensitive range of modern astronomical CCD / CMOS sensors. At the focal position of the e-line (546 nm wavelength), where the human eye is most sensitive, the on-axis Strehl ratio is greater than 99% within the 365 nm–1014 nm wavelength range. The image quality of the optical system of this invention is demonstrated as follows. Figure 4-5 As shown, off-axis image point ellipses, coma, and higher-order aberrations are well eliminated. This invention is suitable for imaging and visual observation.

[0044] The above description is merely an embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A four-element broadband achromatic, spherical aberration-correcting, and coma-correcting refracting telescope optical system, characterized in that: The optical system comprises three spherical lenses and one aspherical lens. Along the optical path, a spherical biconvex lens A, a spherical biconvex lens B, a spherical biconcave lens C, and an aspherical biconvex lens D are arranged sequentially. This optical system provides high-level correction for spherical aberration, axial chromatic aberration, transverse chromatic aberration, coma, and higher-order aberrations over a wide wavelength range from the i-line (365 nm ultraviolet) to the t-line (1014 nm near-infrared). The maximum focal offset of the optical system is less than ±0.00035%. At the focal position of the e-line (546 nm wavelength), where the human eye is most sensitive, the Steller ratio is greater than 99% within the 365 nm – 1014 nm wavelength range. The optical glass used for the four lenses has an internal transmittance of greater than 95% within 10 mm within the 365 nm – 1014 nm wavelength range. The spherical biconvex lens A has a front surface vertex radius of curvature of 769.440 mm and a rear surface vertex radius of curvature of -1024.450 mm. The spherical biconvex lens B has a front surface vertex radius of curvature of 5448.830 mm and a rear surface vertex radius of curvature of -2264.190 mm; the spherical biconcave lens C has a front surface vertex radius of curvature of -1173.420 mm and a rear surface vertex radius of curvature of 539.960 mm; and the aspherical biconvex lens D has a front surface vertex radius of curvature of 403.760 mm and a rear surface vertex radius of curvature of -1829.030 mm.

2. The four-element broadband achromatic, spherical aberration-correcting, and coma-correcting refracting telescope optical system as described in claim 1, characterized in that: The spherical biconvex lens A is made of HOYA FCD100, the spherical biconvex lens B is made of SCHOTT F5, the spherical biconcave lens C is made of OHARA S-LAH97, and the aspherical biconvex lens D is made of HOYA M-FCD1.

3. The four-element broadband achromatic, spherical aberration-correcting, and coma-correcting refracting telescope optical system as described in claim 1, characterized in that: The aspherical biconvex lens D has a front surface that is a quadratic aspherical surface with a conic coefficient k = -0.650, and a rear surface that is spherical.

4. The four-element broadband achromatic, spherical, and coma-correcting refracting telescope optical system as described in claim 1, characterized in that: The air gap between the spherical biconvex lens A and the spherical biconvex lens B is 0.35 mm, the air gap between the spherical biconvex lens B and the spherical biconcave lens C is 1.30 mm, and the air gap between the spherical biconcave lens C and the aspherical biconvex lens D is 1.40 mm.

5. The four-element broadband achromatic, spherical aberration-correcting, and coma-correcting refracting telescope optical system as described in claim 1, characterized in that: The thickness of the spherical biconvex lens A is 14.50 mm; the thickness of the spherical biconvex lens B is 7.20 mm; the thickness of the spherical biconcave lens C is 5.00 mm; and the thickness of the aspherical biconvex lens D is 16.80 mm.

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