The Cassegrain telescope — once considered nearly extinct — is making a strong comeback thanks to the Taiwanese manufacturer GSO. We hope this revival will be permanent, as the design offers many unique advantages and is definitely worth renewed attention.
 
• it cools down faster than Schmidt-Cassegrain and Maksutov-Cassegrain telescopes (similar to RC Newtonians)
• it has no chromatic aberration whatsoever, as it is a fully reflective optical system with no refractive elements (just like RC and Newtonian telescopes)
• it offers a longer focal length than a typical RC or Newtonian, making it parametrically similar to a Maksutov telescope
• it features a very compact construction (similar to RC and Mak telescopes)
• the absence of a lens group allows the Cassegrain to be used for infrared photography
• its long focal length makes collimation easier — a known challenge in RC telescopes, especially when used as travel instruments

 
In general, a Cassegrain system consists of a primary mirror figured as a rotational paraboloid and a secondary mirror shaped as a segment of a rotational hyperboloid. A commonly cited drawback is the difficulty of manufacturing such surfaces — but this is precisely the specialty of GSO. Other limitations include the long focal length and thus a relatively small field of view; however, this often becomes an advantage, as it suppresses edge-of-field aberrations while offering a high imaging scale, beneficial for both photography and visual observation.
 
Recommended applications: visual observations, planetary astrophotography, deep-sky imaging of compact objects using high-sensitivity cameras, infrared photography.

Technical specifications

• optical design: classical Cassegrain telescope
• aperture: 8" / 200 mm
• focal length: 2400 mm
• focal ratio: f/12
• resolving power: 0.59"
• visual limiting magnitude: 13.6 mag
• mirror material: quartz primary and secondary mirrors
• reflectivity: 99% for each mirror
• secondary mirror size: 73.5 mm
• focuser: 2" with 1.25" reducer, 10:1 microfocuser, EAF-compatible
• includes four M90 extension tubes (optical length 25 mm each)
• back focus: 300 mm
• new tube baffling system
• tube diameter: 230 mm
• finder shoe: yes, Vixen standard
• dovetail: yes, Vixen + Losmandy standard
• length: approx. 620 mm
• weight: 7.5 kg

Warranty

24 months

 
Below: sample images taken with our test setup — GSO Cassegrain 8", ZWO ASI 178 MM camera, Baader Solar Continuum filter (sic!); mount: EQ6-R (click to view in full resolution). Author: Przemysław Majewski
/ session from January 2021 /
 

 
 
 
Below: Saturn and Jupiter images submitted by a customer from Italy
setup: ZWO ASI224MC + Celestron Luminos Barlow 2.5x; late summer 2021
author: Alessandro Vinci (published with permission)