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ASA 500 f/9 Cassegrain Reflecting OTA Telescope

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ASA 500 f/9 Cassegrain Reflecting OTA Telescope

ASA 500mm f/9 Cassegrain Telescope - Open Truss Tube

This product by ASA is a classical Cassegrain Telescope optical tube assembly (OTA), which is suitable for serious research or astrophotography. The ASA 500mm f/9 Cassegrain Telescope is a relatively fast (f/9) optical system which is classical, in that the image is formed behind the primary mirror cell, using a perforated parabolic primary mirror and focusing is accomplished by moving the hyperbolic secondary mirror along its axis by a computerized electrical drive system.

The ASA 500mm f/9 Cassegrain Telescope is constructed using a combination of high-grade aluminum components and high strength carbon fiber materials in the form of an open truss tube assembly. Both primary and secondary mirrors are fabricated from AstroSitall, an ultra-low-expansion crystalline glass-ceramic. The mirrors are figured and polished by LOMO Optics, Russia. ASA delivers this telescope with an optical test certificate and an interferogram, which verify the perfect performance of the optics set as built by LOMO. The telescope was designed by Philipp Keller, a German physicist and optical engineer. This scope is suitable for use in remote, automated observing programs, in research applications where high quality imagery is mandatory, or for the most serious astrophotographer.

The ASA 500mm f/9 Cassegrain Telescope has an aperture of 500mm (19.69") or almost 20", a focal ratio of f/9, for a focal length of 4500mm. It has a field of view of 61 arcminutes. This Cassegrain scope will need a corrector lens when it is used with a large format CCD camera. In combination with a focal reducer or a field flattener, also designed by Philipp Keller, the scope can be used with a CCD detector with a diagonal size of 150mm and still produce pin-point stellar images out to the corners. Because your ASA Cassegrain Telescope is designed and manufactured to perform at the diffraction limit, your images will only be limited by the prevailing seeing conditions at your site during image capture and your particular CCD camera equipment.


Some Specifications for the 500mm Cassegrain Telescope by ASA:


  • Aperture: 500mm (19.69")
  • Focal Length: 4500mm
  • Focal Ratio: f/9
  • Back Focus: 365mm (recommended)
  • FOV: 61arcmin
  • Primary Mirror Performance: (Parabolic) - 1/8 wave P/V wavefront accuracy focused, 632nm
  • Primary Mirror Cell Support: 9-point-floating
  • Mirror Set Materials: AstroSitall (LOMO)
  • Mirror Set Coatings: Al + SiO2 with 91% reflectivity
  • Telescope Tube: Combination - aluminum and sandwiched carbon fiber
  • Weight: 187.40lbs (85kg)

This ASA 500mm f/9 Cassegrain Telescope is a special order item and requires a 20% deposit when you place your order, and the balance will be required before the telescope leaves Austria. This deposit is fully refundable as long as you cancel your order before the telescope is imported. Please email OPT or give one of our OPT telescope experts a call at 1-800-483-6287, if you have any questions about this product.

Customer Note: The images represent generic ASA Cass telescopes for illustration purposes. Your telescope might look somewhat different.


Aperture500 mm (19.75")
Back Focus365mm
Dawes Limit3 arcseconds
Focal Length4500 mm
Focal Ratiof/9
Glass TypeAstroSitall
Hightest Magnification1000x
Light Gathering Power5102x
Limiting Magnitude17.2
Optical DesignCassegrain
Tube Weight187.4 lbs