203.2mm / 8.0" Schmidt-Cassegrain, Focal Length: 2032mm, f/10

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The CGEM 800 HD Computerised Telescope from Celestron features a Schmidt-Cassegrain optical system. This compound, or catadioptric, light-path employs a combination of mirrors and lenses that offer a large high-resolution aperture, a shorter tube length, and enhanced portability. This telescope has an 8.0" aperture, a focal length of 2032mm, and a focal ratio of f/10.

EdgeHD optics are designed to produce aberration-free images across a wide visual and photographic field of view. With a significant reduction in off-axis star coma and a flat astrograph quality image plane to the edges of the field of view, the EdgeHD system is capable of imaging diffraction limited stars of 1 arcsec at the edges of a full-frame sensor.

The optical path consists of a zero power corrector plate, a spherical primary mirror, and a secondary mirror along with a set of field flattening lenses integrated into the baffle tube. The resulting imaging plane is 3 times flatter than the field produced by a standard SCT telescope. EdgeHD telescopes feature StarBright XLT multi-layer coatings on the primary and secondary mirrors for increased reflectivity. The corrector is also fully coated to ensure enhanced anti-reflection characteristics.

EdgeHD optics optimise an image circle with a 42mm diameter around the centre of the field of view. This circle completely covers the diagonal of a full-frame DSLR camera or a standard 35mm film frame. As such, it extends significantly beyond the diagonal of APS-C sensors and the smaller chips used in specialised astrophotography CCD cameras. Further refinement of the system's imaging capabilities is managed via mirror tension clutches that help support the primary mirror and minimise its lateral movement. This enhancement is particularly important to astrophotographers as it significantly improves the system's stability and imaging clarity.

The OTA comes with a very useful 9x50 finderscope fitted to its exterior. Due to its wider field of view, this ancillary optic can offer assistance in locating objects to view with the main scope.

Normal image orientation for the EdgeHD design is upside-down and reversed. The 1.25" diagonal inverts this image so it is right-side-up, but reversed. This diagonal directly accepts 1.25" eyepieces, and this kit comes packaged with Celestron's Omni 40mm 1.25" Plossl eyepiece.

The CGEM Mount is fully computerised with a database of over 40,000 celestial objects, and it offers numerous design advantages. While not quite as robust or refined at the CGE PRO, the CGEM is a sturdy and reliable mount with an excellent feature set that fills the niche between the advanced and pro series mounts. The software-assisted all-star polar alignment feature allows the viewer to choose any bright star for alignment of the mount's polar axis, even if the North Star isn't visible. Large hand-knobs offer easy altitude and azimuth adjustments. With just a standard hand-control alignment, the CGE PRO is capable of centring a star to within 5 arc minutes. The NexStar programme's advanced pointing feature further improves the pointing accuracy to as low as 1 arc minute. Additionally, the CGEM's fast slew speeds and precision tracking system deliver outstanding tracking and viewing performance

Key Features

Optical Performance

  • Aperture: 8.0"
  • EFL: 2032 mm, f/10
  • Schmidt-Cassegrain system for aberration-free imaging
  • Premium StarBright XLT coatings for enhanced light transmission
  • EdgeHD optics deliver crisp aberration-free images. They are designed to produce an extremely flat focal plane to match the strict tolerances of the largest commercial CCD detectors. They are capable of imaging a diffraction limited star of 1 arcsec at the very edge of a full frame camera chip.

Construction Details

  • Aluminium tube
  • Mirror support knobs reduce image shift
  • Filtered tube vents release hot air from behind the primary mirror
  • Dovetail rail: included in package - compatible with Celestron's CGE mount
  • Fastar compatible: equipped with a removable secondary mirror for CCD imaging

9x50 finderscope

  • Angle of view: 5.8°
  • Assists in locating objects
  • All mounting hardware is included in kit

Omni 40 mm Eyepiece

  • AFOV: 43°
  • 4-element Plossl
  • Eye Relief: 31 mm
  • Magnification: 51x with 8.0" EdgeHD
  • Accepts Celestron's 1.25" thread-in filters

90° Diagonal

  • Accepts 1.25" eyepieces
  • Image orientation: right-side-up, laterally reversed
  • StarBright XLT multi-layer coatings enhance light transmission
  • Improved brass clamping ring provides a secure no-mar connection

CGEM Computerised Equatorial Mount

  • One 17 lb counterweight
  • Stainless steel tripod: 2.0" legs, accessory tray
  • NexStar technology: 40,000 object database, expanded information on 200+ objects, 100+ user-definable objects. Custom database lists famous deep-sky objects by name and catalog number.
  • All-star" polar alignment uses any bright star for a quick and accurate Polar alignment, even if the North Star is not visible.
  • Software features: mount calibration, database filter limits, hibernate, five alignment procedures.
  • Flash upgradeable hand control software and motor control units for downloading product updates over the Internet.
  • Programmable periodic error correction (PEC)corrects tracking errors.
  • Low cog DC servo motors with integrated optical encoders offer smooth and quiet operation and long-term reliability. The motor armatures are skewed to minimise cogging which is required for low speed tracking.
  • Designated six-pin RJ-12 modular jack, ST-4 compatible guide port, Autoguide port, and auxiliary ports located on the electronic plate for long exposure astrophotography.
  • Double line, LED backlit 16-character LCD hand control simplifies 'Go-To' operation. NexRemote software for computerised telescope control via RS-232 port. Designated six-pin RJ-12 modular jack, ST-4 compatible guide port, Autoguide port, and auxiliary ports located on the electronic plate for long exposure astrophotography. Flash upgradeable hand control, software, and motor control units. Product updates available over the Internet. Internal cable wiring for trouble-free setup and transportation.
  • Precision machined 40 mm diameter steel Polar shafts supported by multiple tapered roller bearings and ball bearings


Optical Design
8.0" / 203.2 mm
Focal Length
2032 mm / 80.0"
Focal Ratio
Resolving Power
Rayleigh: 0.69 arc/sec
Dawes: 0.57 arc/sec
Theoretical Minimum and Maximum Magnification
Min: 29x
Max: 480x
Dovetail Plate
Visual Back
Eyepiece Barrel Diameter
Optical Tube Dimensions
Length: 17.0" / 43.2 cm
OTA: 21.0 lb / 9.53 kg
With tripod/mount: 88 lb / 39.9 kg
Celestron CGEM 800 HD Computerized Telescope
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