The PlaneWave Instruments PW20-RC is a 20 inch (0.51 m) f/6.8 Ritchey-Chrétien (RC) Astrograph 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. More about the Optical Design.
The RC20 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.
The PlaneWave RC20 is available in various types of mirror material. Standard mirror material is borosilicate. The telescope is also available in fused silica optics.
Fused Silicia is a synthetic amorphous silica glass of the highest purity and one of the most transparent glasses made. The optical and thermal properties of fused silica are superior to other types of glass due to its purity. Its transmission and homogeneity exceed those of crystalline quartz without the problems of temperature instability inherent in the crystalline form. Fused Silica has a coefficient of thermal expansion six times lower than Borosilicate (Pyrex) glass, which means that as fused silica cools down, it preserves its shape to a high degree of accuracy. This translates into consistent optical performance and unchanging focus over temperature changes. With its high melting temperature ()~ 1.600 degree Celsius), a very low coefficient of thermal expansion and resistance to thermal shock, fused silica is the material of choice for professional observatories as well as various scientific applications.
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) UpperCage Carbon Fiber Truss Lower Cage Carbon Fiber Truss with Carbon Fiber Light Shroud
Diameter 7.5 inch (191mm) Material Precision Annealed Borosilicate Shape Hyperbolic Coating Broadband AR Coatings (less than .5% reflected from 400 to 700nm)
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%
Carbon Fiber Tube Design Minimizes thermal expansion which causes focus shift with changes in temperature Dovetail expansion joint Allows for the difference in thermal expansion between carbon fiber and aluminum. The expansion joint allows the aluminum dovetail expand and contract without stressing the carbon fiber lower truss Cooling Fans Three cooling fans blow air inside the back of the telescope. This helps the telescope to reach thermal equilibrium quickly. The fans are controlled by a computer if the optional Electronic Focus Accessory (EFA Kit) is purchased.
|Optical Design||Ritchey-Chrétien (RC)|
|Back Focus Distance||5.8" (147 mm) from Racked in Focuser|
|Aperture (mm)||20" (508 mm)|
|Focal Length||3.454 mm (135.98 inch)|
|Central Obstruction||39% of the Primary Mirror Diameter|
|Optical tube length||47 inch (1.194 mm)|
|Optical Tube Weight Copy||140 lbs (64 kg)|