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Schmidt-Cassegrain (SCT)

The Schmidt-Cassegrain is the most versatile telescope design for an observer who wants aperture without a long tube. An 8-inch SCT gives 2032 mm of focal length in a tube about 43 cm long, shows fine detail on Jupiter and Saturn, resolves globular clusters into stars and can be adapted for imaging with a reducer or a HyperStar lens. Celestron has refined this design for more than fifty years, and we carry the full range from the NexStar 5SE to the 14-inch EdgeHD on a CGX-L.

You can buy an SCT as a complete computerized telescope, as a kit on an equatorial mount, or as an optical tube with a CGE-style dovetail for a mount you already own. The choice depends on whether you plan to observe, image the planets, or do long-exposure deep-sky work.

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Celestron EdgeHD 8" OTA - CGE Dovetail

203.2mm (8") EdgeHD Aplanatic Optics 2032mm Focal Length (f/10) 42mm Corrected Image Circle StarBright XLT Optical Coatings Fastar Compatible for ...

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Celestron Nexstar 8SE Computerized Telescope

8" (203.2mm) Schmidt-Cassegrain Optical Tube f/10 Focal Ratio with 2032mm Focal Length StarBright XLT Optical Coatings Computerized Single Fork Ar...

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Celestron NexStar 6SE Computerized Telescope

150mm (5.91") Schmidt-Cassegrain Optical Tube 1500mm Focal Length at f/10 StarBright XLT Optical Coatings Computerized GoTo Mount with 40,000 Obje...

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Celestron NexStar Evolution 8 Telescope

8-inch (203.2mm) Schmidt-Cassegrain OTA f/10 Focal Ratio with StarBright XLT Coatings Integrated WiFi for Full Smartphone or Tablet Control Intern...

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Celestron StarSense Explorer™ DX 5" Smartphone App-Enabled SCT

125mm (5") Schmidt-Cassegrain Optical Tube StarBright XLT Optical Coatings StarSense Explorer App-Enabled Navigation Resolves Detail Down to 0.93 ...

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Celestron Nexstar Evolution 8 EdgeHD with StarSense

8-inch (203.2mm) EdgeHD Aplanatic Optics 2032mm Focal Length (f/10) StarSense AutoAlign Technology Integrated WiFi and 9.6V LiFePO4 Battery Single...

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Celestron Nexstar 5SE Computerized Telescope

125mm (4.92") Schmidt-Cassegrain Telescope 1250mm Focal Length at f/10 Computerized GoTo Single Fork Arm Alt-Azimuth Mount NexStar+ Hand Control w...

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Celestron EdgeHD 9.25" OTA - CGE Dovetail

234.95mm (9.25") EdgeHD Aplanatic Optics 2350mm Focal Length, f/10 Focal Ratio Astrograph-Quality 42mm Corrected Image Circle StarBright XLT Optic...

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Celestron EdgeHD 11" OTA - CGE Dovetail

279.4mm (11") EdgeHD Aplanatic Optics 2800mm Focal Length (f/10) 42mm Flat-Field Image Circle StarBright XLT Optical Coatings 28 lb Optical Tube W...

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Celestron CGEM II 800 EdgeHD Telescope

8-inch (203.2mm) EdgeHD Aplanatic, Flat-Field Optics 2032mm Focal Length at f/10 42mm Image Circle, Optimized for the Central 28mm (APS-C) CGEM II...

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Celestron C9.25 OTA - CGE Dovetail

235mm (9.25") Schmidt-Cassegrain Optical Tube 2350mm Focal Length (f/10) StarBright XLT Optical Coatings 0.49 Arc Second Dawes Resolution Fastar-C...

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Celestron Nexstar Evolution 9.25 Telescope

235mm (9.25") Schmidt-Cassegrain Optical Tube Computerized GoTo Mount with Integrated WiFi Built-in Lithium-Iron Phosphate (LiFePO4) Battery, up t...

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Celestron Nexstar Evolution 6 Telescope

150mm (6") Schmidt-Cassegrain Optical Tube 1500mm Focal Length at f/10 StarBright XLT Optical Coatings Integrated WiFi for Smartphone and Tablet C...

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Celestron CPC Deluxe 925 HD Computerized Telescope

235mm (9.25") EdgeHD Aplanatic Schmidt-Cassegrain Optics 2350mm Focal Length at f/10 Optimized 42mm Image Circle for Full-Frame Sensors StarBright...

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Celestron CPC Deluxe 800 HD Computerized Telescope

8" (203.2mm) EdgeHD Optical Design 2032mm Focal Length (f/10) 42mm Corrected Image Circle Computerized Dual Fork Arm GoTo Mount 40,000+ Object Nex...

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Celestron CGEM II 1100 SCT

11-inch (279.4mm) Schmidt-Cassegrain Optical Tube 40 lb (18 kg) Instrument Payload Capacity CGEM II Computerized Equatorial Mount StarBright XLT O...

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Celestron Advanced VX 8" SCT

8" (203.2mm) Schmidt-Cassegrain Optical Tube 2032mm Focal Length at f/10 Advanced VX Computerized German Equatorial Mount 30 lb (13.6 kg) Instrume...

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Celestron EdgeHD 14" OTA - CGE Dovetail

14" (356mm) EdgeHD Aplanatic Schmidt-Cassegrain Optics 3910mm Focal Length at f/11 42mm Flat-Field Image Circle 0.33 Arc Second Dawes Resolution L...

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Celestron CPC Deluxe 1100 HD Computerized Telescope

11" (279.4mm) EdgeHD Aplanatic Optical Design 2800mm Focal Length at f/10 42mm Image Circle for Full-Frame Sensors Computerized Dual Fork Arm Alt-...

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Celestron CPC 925 GPS (XLT) Computerized Telescope

235mm (9.25") Schmidt-Cassegrain Optical Tube Fully Computerized Dual Fork Arm Alt-Azimuth Mount Internal 16-Channel GPS for Automatic Alignment D...

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Celestron CPC 800 GPS (XLT) Computerized Telescope

8-inch (203.2mm) Schmidt-Cassegrain Optical Tube Assembly 2032mm Focal Length at f/10 Computerized Dual Fork Arm Alt-Azimuth Mount Internal 16-Cha...

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Celestron CPC 1100 GPS (XLT) Computerized Telescope

11" (279.4mm) Schmidt-Cassegrain Optical Tube Assembly 1593x the light gathering power of the human eye 0.42 Arc Second Dawes Limit Resolution Com...

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Celestron CGX-L Equatorial 925 SCT

235mm (9.25") Schmidt-Cassegrain Optical Tube 75 lb (34 kg) instrument load capacity on the CGX-L mount, not including counterweights 2350mm focal...

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Celestron CGX-L Equatorial 925 HD Telescope

9.25" (234.95mm) EdgeHD Aplanatic Schmidt-Cassegrain Optics 2350mm Focal Length at f/10 42mm Optimized Image Circle for Full-Frame Sensors CGX-L C...

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Standard SCT or EdgeHD?

  • Standard SCT (XLT coatings): Superb for visual observing and planetary imaging. The field is slightly curved, which only shows in deep-sky imaging with larger sensors.
  • EdgeHD: Adds corrector lenses in the baffle tube to produce a flat, coma-free field. The best choice for deep-sky imaging and for wide-field eyepieces at the edge of the view.
  • Reducers: Standard SCTs use the f/6.3 reducer-corrector. EdgeHD tubes use their own 0.7x reducer, which brings them to about f/7 with a flat field. See field flatteners and reducers.
  • HyperStar: On compatible tubes, a Starizona HyperStar replaces the secondary mirror to give roughly f/2 for very fast imaging.

Which Mount?

  • NexStar SE and Evolution: Single and dual-arm alt-az GoTo mounts for 5 to 9.25-inch tubes. Excellent for visual and planetary work.
  • CPC: Heavy fork mount with GPS for 8 to 11-inch tubes. Very steady for visual observing.
  • Advanced VX, CGEM II, CGX, CGX-L: Equatorial mounts for imaging. We size them for imaging payload, not visual payload.

Getting the Best from an SCT

  • Cool-down: An 11-inch SCT can need an hour to settle in winter. Planetary detail appears only once the tube air and mirror reach outside temperature.
  • Collimation: A quick star test at high power tells you if the secondary needs a touch. Bob's Knobs make it a tool-free job.
  • Dew control: The front corrector is a dew magnet. A dew shield is the minimum, and a heater strip with a controller is best on humid Canadian summer nights.
  • Mirror shift: SCTs focus by moving the primary mirror. For imaging, a rear electronic focuser and mirror locks on EdgeHD tubes keep focus stable.

Schmidt-Cassegrain Telescopes: Frequently Asked Questions

What size SCT should I buy?

The 8-inch is the classic balance of aperture, weight and price. The 9.25-inch has a reputation for slightly sharper planetary views. The 11 and 14-inch reward observers with a permanent setup.

Is an SCT good for deep-sky imaging?

Yes with the right setup: EdgeHD optics, a reducer, a solid equatorial mount and off-axis guiding. Long focal length makes it demanding, so many imagers start with a refractor and add an SCT later.

Can I use an SCT for planetary imaging?

It is one of the best tools for it. Add a planetary camera, and a Barlow if your pixels are small, and capture video on nights of steady seeing.

Choosing a Schmidt-Cassegrain?

Tell us whether you plan to observe, image planets or image deep-sky. We will match the tube, mount and accessories.