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Astronomical Telescopes
Published in Daniel Malacara-Hernández, Zacarías Malacara-Hernández, Handbook of OPTICAL DESIGN, 2017
Daniel Malacara-Hernández, Zacarías Malacara-Hernández
A two-mirror telescope or camera is formed by a large concave mirror, called the primary mirror, and a small concave or convex mirror, called the secondary mirror, in front of it, to reflect back the light toward the primary mirror. The image is formed behind the primary mirror, with the light passing through a hole in its center. If the secondary mirror is convex, as in Figure 14.2, we have a Cassegrain telescope, but if the secondary mirror is concave, we have a Gregory (or Gregorian) telescope, as in Section 14.4.5. The Cassegrain telescope was invented in 1672 by Guillaume Cassegrain in France. The effective focal length F is positive for the Cassegrain and negative for the Gregory telescope. These telescopes have been studied in great detail and described by Bouwers (1946), Yoder et al. (1953a, 1953b), Jones (1954), Baker (1963), DeVany (1963), Malacara (1965), Schulte (1966a, 1966b), Bowen (1967), Wynne (1968), Meinel (1969), Wetherell and Rimmer (1972), Cornejo and Malacara (1973, 1975), Gascoigne (1973), Shafer (1977), Schroeder (1978, 1987), and Toyoda (2011).
Telescopes
Published in Daniel Malacara-Hernández, Brian J. Thompson, Fundamentals and Basic Optical Instruments, 2017
Marija Strojnik, Maureen S. Kirk
Strictly speaking, the simplest on-axis two-mirror telescope is a Newtonian, using just a beam-turning mirror to bring the focal plane and associated instruments out of the incoming beam. The two basic refractive telescopes may likewise be implemented as two-mirror systems. Figure 11.20b illustrates the case when the secondary mirror is divergent, resulting in an appreciably shorter instrument length and a smaller central obscuration, generally adopted for astronomical telescopes. This layout is known as a Cassegrain telescope when the primary mirror is a paraboloid and the secondary mirror is a hyperboloid. This configuration is necessary for the coincidence of the focal lengths behind the secondary mirror. The image formed by the primary mirror alone is smaller than the final image formed by the Cassegrain telescope because the secondary mirror actually magnifies it. When the secondary mirror is concave, there is a common focal point between the mirrors and the system is somewhat longer than the sum of the focal lengths. This layout is exhibited in Figure 11.20c, featuring the advantage that the final image just outside of the primary mirror is erect (head-up). This layout may be used for terrestrial applications. The configuration known as a Gregorian telescope incorporates an on-axis section of a paraboloid for the primary mirror, and an on-axis ellipsoid for the secondary mirror. In accordance with the established terminology, we will use shorter terminology and leave out on-axis, when not explicitly referring to an off-axis configuration, and section though this term is always implied.
Optics and optical instruments
Published in Andrew Norton, Dynamic Fields and Waves, 2019
A converging objective mirror and a converging eyepiece lens can be used to construct a reflecting telescope. The Newtonian and Cassegrainian telescope designs use a secondary mirror to enable the image to be directed to the eye or other light-sensitive recording device. Parabolic mirrors or Schmidt correcting plates are used to overcome the problems of spherical aberration.
Self-interference polarisation pantographer method to fabricate Pancharatnam-Berry phase optical elements
Published in Liquid Crystals, 2023
Zhiqing Liang, Xiaoxian He, Dongmei Gu, Fucai Liu, Xiangru Wang, Tibin Zeng, Yingjie Zhou, Fan Fan, Wei Hu
On the step of UV exposure, a DPSS UV laser (Newopto-375–50) with a wavelength of 375 nm was used. The laser intensity was 1.068 mW/cm2, tested at the sample position. To meet the ∼0.5J/cm2 full dosage of SD1 material, the exposure time was set as 10 minutes. The optical setup was constructed according to Figure 1, a standard Cassegrainian system consisting of a parabolic primary mirror and a hyperbolic secondary mirror. The main parameters of the system include focal length f = 200 mm and the central obscuration ratio of 0.3. The radii of curvature of the vertices of the primary mirror and the secondary mirror are R1 = 200.6 and R2 = 40.07, and the distance between them is d = 70.2 mm.
A high-precision apparatus for dimensional characterization of highly stable materials in space applications
Published in Mechanics of Advanced Materials and Structures, 2022
Baolong Sun, Hansi Zhang, Chuang Xue, Weihui Shang
The demand for lightweight design continues to increase in aeronautical and space structures, where the components are made up of composites instead of metals. Advanced carbon-fiber reinforced plastic (CFRP) materials are well suited for stable space structures due to their light weight, high stiffness and low coefficient of thermal expansion (CTE). In space telescope structures, all optical components and scientific instruments are installed on a truss structure. The deformation of each component directly affects the relative position between the primary mirror and secondary mirror. Therefore, it is very important to ensure the stability of the telescope truss structure to obtain the desired quality of the optical images.
Optical design of a null test for off-axis three-mirror system based on refractive-diffractive zoom hybrid compensator
Published in Journal of Modern Optics, 2022
Lai Xiaoxiao, Chang Jun, Li Yiting, Ji Zhongye, Cao Jiajing, Li Dongmei
The results of tolerance analysis are shown in Figure 7. As can be seen, the probability of the residual wave aberration reaching 0.07 RMS at a wavelength of 632.8 nm is 50% for the primary mirror test system, 40% for the secondary mirror test system, and 80% for the tertiary mirror test system. If the test wavelength is above 1770 nm, the residual wave aberration of primary mirror, secondary mirror and tertiary mirror test system will reduce to 0.025 RMS, and the probabilities are 50%, 40%, 80% respectively. These results prove the feasibility of the proposed test method.