Abstract

We describe here an off-axis design for a 4.0-m astronomical telescope. We show that the geometric optical performance of this configuration can equal that of an on-axis conventional configuration while the diffractive performance fundamentally surpasses conventional telescopes because of the absence of pupil obstruction. The specific optical design described here uses a single off-axis primary mirror to obtain three distinct final focus ports: an f/10 port (with corrector) for wide-field imaging and spectroscopy with a field of view (FOV) of 15 arc min; a small-field, 2-reflection f/10 port suitable for polarimetry and coronagraphy; and a slower, f/16 (3-reflection) port with a 7 arc min FOV. For general astronomical observations requiring high optical throughput and low scattered light, this design is superior to conventional Ritchey–Chretien optical configurations.

© 1998 Optical Society of America

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References

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  1. J. H. Burge, “Applications of computer generated holograms for interferometric measurement of large aspheric optics,” in International Conference on Optical Fabrication and Testing, T. Kasai, ed., Proc. SPIE2576, 258–269 (1995).
    [CrossRef]
  2. G. Cecil, J. R. Kuhn, G. Moretto, J. Baldwin, H. Dottori, “SOAR scientific & technical requirements,” SOAR Project Internal Report (National Optical Astronomy Observatories, Tucson, Ariz., 1997).
  3. J. R. Kuhn, “SOAR-MSU astronomers report on scattered light,” MI-48823 (Michigan State University, East Lansing, Mich., 1997).
  4. G. Moretto, G. R. Lemaı̂tre, T. Bactivelane, M. Wang, M. Ferrari, S. Mazzanti, B. Di Biagio, E. F. Borra, “Zernike polynomials for correcting off-axis aberrations of fixed primary mirrors. 2. Optical testing and performance evaluation,” Astron. Astrophys. Suppl. Ser. 114, 379–386 (1995).
  5. G. Moretto, E. F. Borra, “Corrector design with active vase mirrors that allows a fixed telescope to access a large region of the sky,” Appl. Opt. 36, 2114–2122 (1997).
    [CrossRef] [PubMed]
  6. M. Wang, G. Moretto, E. F. Borra, G. R. Lemaı̂tre, “A simple active corrector for liquid mirror telescope at large zenith angles,” Astron. Astrophys. 284, 344–353 (1994).

1997

1995

G. Moretto, G. R. Lemaı̂tre, T. Bactivelane, M. Wang, M. Ferrari, S. Mazzanti, B. Di Biagio, E. F. Borra, “Zernike polynomials for correcting off-axis aberrations of fixed primary mirrors. 2. Optical testing and performance evaluation,” Astron. Astrophys. Suppl. Ser. 114, 379–386 (1995).

1994

M. Wang, G. Moretto, E. F. Borra, G. R. Lemaı̂tre, “A simple active corrector for liquid mirror telescope at large zenith angles,” Astron. Astrophys. 284, 344–353 (1994).

Bactivelane, T.

G. Moretto, G. R. Lemaı̂tre, T. Bactivelane, M. Wang, M. Ferrari, S. Mazzanti, B. Di Biagio, E. F. Borra, “Zernike polynomials for correcting off-axis aberrations of fixed primary mirrors. 2. Optical testing and performance evaluation,” Astron. Astrophys. Suppl. Ser. 114, 379–386 (1995).

Baldwin, J.

G. Cecil, J. R. Kuhn, G. Moretto, J. Baldwin, H. Dottori, “SOAR scientific & technical requirements,” SOAR Project Internal Report (National Optical Astronomy Observatories, Tucson, Ariz., 1997).

Borra, E. F.

G. Moretto, E. F. Borra, “Corrector design with active vase mirrors that allows a fixed telescope to access a large region of the sky,” Appl. Opt. 36, 2114–2122 (1997).
[CrossRef] [PubMed]

G. Moretto, G. R. Lemaı̂tre, T. Bactivelane, M. Wang, M. Ferrari, S. Mazzanti, B. Di Biagio, E. F. Borra, “Zernike polynomials for correcting off-axis aberrations of fixed primary mirrors. 2. Optical testing and performance evaluation,” Astron. Astrophys. Suppl. Ser. 114, 379–386 (1995).

M. Wang, G. Moretto, E. F. Borra, G. R. Lemaı̂tre, “A simple active corrector for liquid mirror telescope at large zenith angles,” Astron. Astrophys. 284, 344–353 (1994).

Burge, J. H.

J. H. Burge, “Applications of computer generated holograms for interferometric measurement of large aspheric optics,” in International Conference on Optical Fabrication and Testing, T. Kasai, ed., Proc. SPIE2576, 258–269 (1995).
[CrossRef]

Cecil, G.

G. Cecil, J. R. Kuhn, G. Moretto, J. Baldwin, H. Dottori, “SOAR scientific & technical requirements,” SOAR Project Internal Report (National Optical Astronomy Observatories, Tucson, Ariz., 1997).

Di Biagio, B.

G. Moretto, G. R. Lemaı̂tre, T. Bactivelane, M. Wang, M. Ferrari, S. Mazzanti, B. Di Biagio, E. F. Borra, “Zernike polynomials for correcting off-axis aberrations of fixed primary mirrors. 2. Optical testing and performance evaluation,” Astron. Astrophys. Suppl. Ser. 114, 379–386 (1995).

Dottori, H.

G. Cecil, J. R. Kuhn, G. Moretto, J. Baldwin, H. Dottori, “SOAR scientific & technical requirements,” SOAR Project Internal Report (National Optical Astronomy Observatories, Tucson, Ariz., 1997).

Ferrari, M.

G. Moretto, G. R. Lemaı̂tre, T. Bactivelane, M. Wang, M. Ferrari, S. Mazzanti, B. Di Biagio, E. F. Borra, “Zernike polynomials for correcting off-axis aberrations of fixed primary mirrors. 2. Optical testing and performance evaluation,” Astron. Astrophys. Suppl. Ser. 114, 379–386 (1995).

Kuhn, J. R.

J. R. Kuhn, “SOAR-MSU astronomers report on scattered light,” MI-48823 (Michigan State University, East Lansing, Mich., 1997).

G. Cecil, J. R. Kuhn, G. Moretto, J. Baldwin, H. Dottori, “SOAR scientific & technical requirements,” SOAR Project Internal Report (National Optical Astronomy Observatories, Tucson, Ariz., 1997).

Lemai^tre, G. R.

G. Moretto, G. R. Lemaı̂tre, T. Bactivelane, M. Wang, M. Ferrari, S. Mazzanti, B. Di Biagio, E. F. Borra, “Zernike polynomials for correcting off-axis aberrations of fixed primary mirrors. 2. Optical testing and performance evaluation,” Astron. Astrophys. Suppl. Ser. 114, 379–386 (1995).

M. Wang, G. Moretto, E. F. Borra, G. R. Lemaı̂tre, “A simple active corrector for liquid mirror telescope at large zenith angles,” Astron. Astrophys. 284, 344–353 (1994).

Mazzanti, S.

G. Moretto, G. R. Lemaı̂tre, T. Bactivelane, M. Wang, M. Ferrari, S. Mazzanti, B. Di Biagio, E. F. Borra, “Zernike polynomials for correcting off-axis aberrations of fixed primary mirrors. 2. Optical testing and performance evaluation,” Astron. Astrophys. Suppl. Ser. 114, 379–386 (1995).

Moretto, G.

G. Moretto, E. F. Borra, “Corrector design with active vase mirrors that allows a fixed telescope to access a large region of the sky,” Appl. Opt. 36, 2114–2122 (1997).
[CrossRef] [PubMed]

G. Moretto, G. R. Lemaı̂tre, T. Bactivelane, M. Wang, M. Ferrari, S. Mazzanti, B. Di Biagio, E. F. Borra, “Zernike polynomials for correcting off-axis aberrations of fixed primary mirrors. 2. Optical testing and performance evaluation,” Astron. Astrophys. Suppl. Ser. 114, 379–386 (1995).

M. Wang, G. Moretto, E. F. Borra, G. R. Lemaı̂tre, “A simple active corrector for liquid mirror telescope at large zenith angles,” Astron. Astrophys. 284, 344–353 (1994).

G. Cecil, J. R. Kuhn, G. Moretto, J. Baldwin, H. Dottori, “SOAR scientific & technical requirements,” SOAR Project Internal Report (National Optical Astronomy Observatories, Tucson, Ariz., 1997).

Wang, M.

G. Moretto, G. R. Lemaı̂tre, T. Bactivelane, M. Wang, M. Ferrari, S. Mazzanti, B. Di Biagio, E. F. Borra, “Zernike polynomials for correcting off-axis aberrations of fixed primary mirrors. 2. Optical testing and performance evaluation,” Astron. Astrophys. Suppl. Ser. 114, 379–386 (1995).

M. Wang, G. Moretto, E. F. Borra, G. R. Lemaı̂tre, “A simple active corrector for liquid mirror telescope at large zenith angles,” Astron. Astrophys. 284, 344–353 (1994).

Appl. Opt.

Astron. Astrophys.

M. Wang, G. Moretto, E. F. Borra, G. R. Lemaı̂tre, “A simple active corrector for liquid mirror telescope at large zenith angles,” Astron. Astrophys. 284, 344–353 (1994).

Astron. Astrophys. Suppl. Ser.

G. Moretto, G. R. Lemaı̂tre, T. Bactivelane, M. Wang, M. Ferrari, S. Mazzanti, B. Di Biagio, E. F. Borra, “Zernike polynomials for correcting off-axis aberrations of fixed primary mirrors. 2. Optical testing and performance evaluation,” Astron. Astrophys. Suppl. Ser. 114, 379–386 (1995).

Other

J. H. Burge, “Applications of computer generated holograms for interferometric measurement of large aspheric optics,” in International Conference on Optical Fabrication and Testing, T. Kasai, ed., Proc. SPIE2576, 258–269 (1995).
[CrossRef]

G. Cecil, J. R. Kuhn, G. Moretto, J. Baldwin, H. Dottori, “SOAR scientific & technical requirements,” SOAR Project Internal Report (National Optical Astronomy Observatories, Tucson, Ariz., 1997).

J. R. Kuhn, “SOAR-MSU astronomers report on scattered light,” MI-48823 (Michigan State University, East Lansing, Mich., 1997).

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Figures (10)

Fig. 1
Fig. 1

(a) RC off-axis, f/16 design. An off-axis section of the f/1 parent mirror (k = -1.001513) is used as primary mirror M 1. The secondary M 2 is also an off-axis section of a conic (k = -2.01749) mirror. The tertiary M 3 is a flat-fold mirror with aspheric terms. (b) The figure deviation from the best-fit sphere for the 0.9-m M 3 aspherical flat mirror.

Fig. 2
Fig. 2

RC off-axis, f/16 design. The EED for each field position F n (x, y), as defined in Table 1, across the 7 arc min FOV. Because of the bilateral symmetry of the system, we represent only half-FOV.

Fig. 3
Fig. 3

(a) PSF’s computed across the 7.0 arc min FOV. The solid circle represents the ideal position and the dashed circle is the real position of the centroid coordinates for each field position F n (x, y). (b) The FOV distrortion control. The layout shows the centroid (×) and the chief-ray (+) coordinates for the FOV’s nine field positions F n (x, y) and F 1F 9, defined in Table 1, on the focal plane.

Fig. 4
Fig. 4

RC off-axis, f/10 design. (a) The same off-axis primary mirror M 1 that was optimized for the f/16 design is used. The secondary M 2 is a dedicated secondary and also is an off-axis section of a conic (k = -3.49918) mirror. (b) The corrector S n specifies the surface of each lens and K = 0 + ASPH means that the lens has a spherical surface with some aspherical terms. Both figures are to scale.

Fig. 5
Fig. 5

Figure deviation from the best spheres for the f/10 corrector’s aspheric surfaces (Fig. 7). (a, Top) The second surface (S5) of the 330-mm diameter corrector’s first lens (S4 and S5). (a, Bottom) The second surface (S7) of the 290-mm diameter corrector’s second lens (S6 and S7). The surfaces (b, Top) (S8) and (b-bottom) (S9) of the 256-mm diameter corrector’s third lens (S8 and S9).

Fig. 6
Fig. 6

RC off-axis, f/10 design. The EED for each field position F n (x, y) as defined in the small figure left-top, across the 15 arc min diameter and 12 × 12 arc min FOV. Because of the bilateral symmetry of the system, we represent only half-FOV.

Fig. 7
Fig. 7

PSF’s computed across the 15.0 arc min FOV. Each field position F n (x, y) is defined in the small figure on the left. Because of the bilateral symmetry of the system, we represent only half-FOV.

Fig. 8
Fig. 8

FOV f/10 distrortion control. The layout shows the centroid (×) and the chief-ray (+) coordinates for the FOV’s nine field positions F n (x, y) as defined in Table 2.

Fig. 9
Fig. 9

RC off-axis, f/9.13 design. The same off-axis primary mirror M 1 that was optimized to the f/16 design and the same secondary M 2 optimized to the f/10 design was used to get a two-mirrors bare design over 3.0 arc min FOV.

Fig. 10
Fig. 10

PSF’s computed across the 3.0 arc min FOV. The solid circle shows the ideal position and the dashed circle shows the real position of the centroid coordinates for each field position F n (x, y) defined in Table 3.

Tables (3)

Tables Icon

Table 1 RC off-axis, f/16 designa

Tables Icon

Table 2 Radial Energy Distribution of the Geometric SD that Characterizes the Correction over the 15 arc min FOVa

Tables Icon

Table 3 Radial Energy Distribution of the Geometric SD that Characterizes the Correction over the 3 arc min FOV for a Two-Mirrors Bare Design

Equations (4)

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Astm 3   λ W 22 = sin 2   α R   ρ 2   cos 2   θ ,
Coma 3   λ W 31 = 1 R 2 cos   α   sin   α   -   2   sin   α ρ 3   cos   θ ,
Astm 5   λ W 42 = 3   sin 2   α R 3 2 + cos   α ρ 4   cos 2   θ ,
Tri-Coma 5     λ W 33 = 2   sin 3   α R 2   ρ 3   cos 3   θ ,

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