Ritchey Chretien 250

300mm f/6 MDDK Astrograph
600mm - 1000mm mm f/5.6 ECDKs

Ritchey-Chretien telescopes are popular for astrophotography and professional observatories due to their relatively large corrected field and absence of coma. The tube assembly is semi-ruggedised and is of fail-safe construction. The mirror supports in instruments under 600 mm are high precision floatation cells with full edge supports, larger mirrors are supported with kinematic face and edge supports. The focuser is included as standard, this is achieved by moving the secondary mirror

Price (Excl.VAT)


Aperture (mm)250
Recommended mount typeGEM
Tube tubeClosed
Focal length (mm)1500
Tube length (operating)625
OTA Weight (kg)12
Back focus175
Focal ratio F/6
Cooling fansPrimary mirror
Mirror coatingsEnhanced Aluminium + SiO2 protective layer
FocuserIntegrated JTW Rhino
Clear aperture (mm)50
Tube constructionCarbon fiber
Optical surface quality (Strehl, PTV)0.97, 1/10
Primary mirror substrateSchott Supremax 33
Primary mirror cell9 point floatation cell
Primary baffleSolid with micro-baffling
Secondary mirror substrateSchott Supremax 33
Secondary mirror cell3 point floatation cell
Secondary baffleSolid with micro-baffling
BoltingA4 Stainless steel
Metal protectionDual
Surface treatmentAluminium – 20 micron hard-coat anodising
PaintExterior grade powdercoat (environmentally friendly)
Anti dew systemOptional