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19 November 1998 Aplanatic Wolter Type-I telescope design: is there a practical advantage?
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It is well known that normal incidence, aplanatic telescope designs performed better at low field angles than ones corrected only for spherical aberration. This is why most large astronomical telescopes fabricated in the past fifty years have been of the Ritchey-Chretien design rather than of the classical Cassegrain design. For the relatively new field of x-ray/EUV astronomy, the Wolter type-I and Wolter Type-II grazing incidence designs have been extensively utilized. Both types consist of a paraboloidal primary mirror coaxial with a confocal hyperboloidal secondary mirror.The Wolter Type-II is the grazing incidence analog of the classical Cassegrain design. 'Aplanatic' versions of both the Wolter Type-I and the Wolter Type-II grazing incidence x-ray/EUV telescopes have been discussed in detail in the literature, and are widely touted as being superior designs. And indeed they are, at small field angles where coma-like aberrations dominate astigmatism-like ones. However, scattering effects and other practical optical fabrication tolerances prevent these grazing incidence telescope designs from being near diffraction-limited at the x-ray/EUV wavelengths, even on-axis. Since the scattering effects dominate residual coma-like design errors at the small field angles, there is negligible improvement in performance and perhaps a significant disadvantage in cost and schedule of fabrication. Comparison of performance predictions for the classical versus 'aplanatic' Wolter Type-I x-ray telescopes will be presented for the special case of the solar x-ray imager. SXI is a soft x-ray, solar telescope which is expected to become a standard subsystem aboard the next generation of NOAA/GOES weather satellites.
© (1998) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Patrick L. Thompson and James E. Harvey "Aplanatic Wolter Type-I telescope design: is there a practical advantage?", Proc. SPIE 3444, X-Ray Optics, Instruments, and Missions, (19 November 1998);


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