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20 inch Ritchey-Chrétien Optical Tube Assembly

SKU 200125Q

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The PlaneWave Instruments PW20-RC is a 20 inch (0.51 m) f/6.8  Ritchey-Chrétien (RC) Astrograph telescope. The PW20-RC has a dual carbon-fiber truss design, with 3 cooling fans ejecting air from the back of the telescope.  The instrument weight is 140 lbs (64 kg) and comes standard with a back plate retaining ring ready to accept the focuser of your choice. PlaneWave's CDK astrographs have become the telescopes of choice for universities, industry, and astrophotographers around the world, and now PlaneWave offers the PW-RC series to meet the custom needs of the scientific community.

The PW20-RC in its native format (no field flattening lenses) uses only a primary and secondary mirror with reflective coatings. This can be useful when making observations primarily on-axis and wide field imaging is not a concern.

Also available with the CDK (Corrected Dall-Kirkham) optical design


Optical System

Optical Design Ritchey-Chrétien (RC)
Aperture 20 inch (508 mm)
Focal Length 3454 mm (135.98 inch)
Focal ratio F/6.8
Central Obstruction 39% of the Primary Mirror Diameter
Back Focus from Racked in Focuser 5.8 inch (147 mm)
Weight 140 lbs (63.5 kg)
OTA Length 47 inch (1,194 mm)
Upper Cage Carbon Fiber Truss
Lower Cage Carbon Fiber Truss with Carbon Fiber Light Shroud

Secondary Mirror

Diameter 7.5 inch (191mm)
Material Precision Annealed Borosilicate
Shape Hyperbolic
Coating Broadband AR Coatings (less than .5% reflected from 400 to 700nm)

Primary Mirror

Optical Diameter 20 inch (508 mm)
Outer Diameter 20.5 inch (521 mm)
Shape Hyperbolic
Material Precision Annealed Borosilicate or Fused Silica
Coating Enhanced Aluminum – 96%


Crated Shipping Weight 291 lbs   (132.0 kg)
Crate Width 32 inch   (813 mm)
Crate Height 36 inch   (914 mm)
Crate Length 59 inch   (1,499 mm)

Included Accessories

Primary Mirror Cover The Primary Mirror Cover protects the primary mirror.
Printed Instructions For Collimation and Spacing
12VDC Power Supply (18778) Provides power for the fans (Not included for European Orders)
Wrench Set (5812A35 ) English Hex Wrenches (European Orders Only)
Recommended Accessories

Mounting Bracket for Finderscopes (125360)

Finderscope and Mounting Bracket (200985)

Visual Adapter – CDK20 (200399)

Delta T Heater Part (240901)

Hendrick Focuser (200340)

IRF90 – Integrated Rotating Focuser (600180)

EFA kit Electronic Focuser (EFA)

Light Shroud CDK20 (200970)

Dovetail Clamp CDK20 (200919)

Piggyback Dovetail Bars (200990)

L-500 Direct Drive Mount (600550)