20-inch (half-meter) Ritchey-Chretien research grade
telescope for sale


This instrument is a well cared for f/8, research grade 20-inch RCOS telescope Carbon Truss telescope that produced vitually all of the images seen on Cosmotograpy.com. Exposures collected with this instrument have been used in over 14 peer-reviewed scientific papers published in the Astrophysical Journal, Monthly Notices of the Royal Astronomical Society (MNRAS) and Astronomy & Astrophysics.

Images produced with this telescope have graced the covers of numerous books, featured in television programs and been included in dozens of magazines, books and calendars all over the world. Over 25 APOD's were also cited for images obtained with this instrument. So, the optical and mechanical qualities are superb.

Telescope Description

Basic Telescope Characteristics:
  • Diameter of Objective Mirror = 508 mm
  • Focal length = 4115 mm
  • F-ratio = f/8.1
  • Light Collecting Power (LMP) = 4032 x
  • Resolving Power (RP) = 0.28 arc second
  • Intrinsic Visual Limiting Magnitude = 14.5 mag
  • Magnification Power : min = 63x, max = 627x
  • Manufacturer: RC Optical Systems

20RC Carbon Truss Telescope Specifications:
  • 20-inch F/8.1 Ritchey-Chrétien Optics certified to 1/25 wave RMS or better.
  • Fringe analysis and interferometric data supplied with optics.
  • Enhanced Aluminum (SiO2/TiO2) overcoat - 96.9% reflectivity.
  • Low Expansion, light weight Carbon Fiber Truss tubes for superior performance and stability.
  • Carbon / Nomex Honeycomb Light Shroud with End Ring.
  • Honeycomb CNC Machined 6061 Aluminum Back Plate.
  • Precision Secondary Mirror Focuser.
  • 2-Stage Primary mirror baffle with internal knife-edge light stops.
  • Secondary light baffle.
  • 6061 Aluminum Mounting Rings - CNC Machined.
  • 6061 Aluminum Secondary Support Ring - CNC Machined.
  • Active Cooling.
  • RCOS "Focus and Forget" Technology.
  • CNC Machined "light weight" dovetail plates - top and bottom.

Specifications of 20” Ritchey-Chrétien Optics:
  • Primary Diameter 508 mm
  • Primary Focal Length 1524 mm
  • Primary-Secondary Spacing 1016 mm
  • Effective Focal Length 4114.8 mm

Other Specifications:
  • Carbon Tube O.D. 629.92 mm
  • Overall Length 1479.55mm
  • Secondary Focus Travel 25.4 mm
  • Secondary Position Resolution 0.00635mm
  • Back-plate Focus Distance 254 mm
  • Weight < 63.50 kg
  • Back-Plate Payload Capacity: 13.61 kg
  • Temperature: -6.67 to 37.78 100 degrees C ambient
  • Insulation: Carbon Tube / Truss to minimize thermal gradients.
  • Coatings: Enhanced aluminum - 96.9% reflectivity.
Engineering drawing of 20RC Carbon Truss

Optical characteristics:

  • Fringe analysis and interferometric measurements furninshed by the the manufactuer indicates a P-V RMS of .043 and a strehl ratio of .929 (greater than 1/20 wave)
  • The primary is oversized and measures almost 21 inches in diameter. A 1/2 inch machined mirror mask reduces the diameter to slightly over 20 inches.
  • Additional stray light prevention mods eliminate internal reflections
  • The optical acuity of the telescope is exceptional.

  • Telescope primary mirror interferogram
    Telescope primary mirror optical information

    Sale inclusions:

  • Half-meter (20-inch) RCOS Carbon-truss OTA with a carbon truss and Astro-Sitall zero-expansion mirrors,
  • 2 X Telescope Command Center 2 (primary and spare) ,
  • RCOS light-weight dovetail plates,
  • 70mm Precision Instrument Rotator (PIR),
  • Monster MOAG
  • numerous RCOS back focus adapters and spacers for your camera and a monster MOOG.

  • Price:

  • USD $35,000, CONUS delivery included
  • Telescope is offered as-is
  • Mechanical condition is excellent and like new
  • Optical condition is very good
  • Acceptable forms of payment: personal or cashier's check, money order, bank-to-bank money transfer, cash (your payment transaction must first clear the bank before the sale is considered final)

    Frequently Asked Questions:

  • Where can I get support for this telescope?
    • The original manufacturer of this telescope, RC Optical Systems, has been sold to Deep Sky Instruments. The new owners are providing mechanical support for all RCOS telescopes in the field. Support for the electronics is provided by Right Ascension Limited.
  • Is it possible to upgrade this telescope?
    • Yes. The telescope can be upgraded by Deep Sky Instruments. This includes adding a 100mm Precision Instrument Rotator and field flatener. You may also upgrade the Telescope Command Center (TCC) to the latest version, now called the Telescope Interface Module (TIM), through Right Ascension Limited.
  • Will you ship the telescope to an overseas buyer?
    • Yes. I will have the telescope professionally packed so arrives at its overseas destination in perfect condition.

    Please contact R. Jay GaBany at rj2010@cosmotography.com to arrange your purchase or ask for more information.

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