Portable, Light Weight, and Economical
The GSO 200mm (approx. 8″) f/4 imaging Newtonian offers a fast focal ratio that’s ideal for capturing wide-field images of hundreds of celestial objects. The 800mm focal length keeps the tube length to a compact 27.75″, making it easier to guide during extended exposures. With a total weight of only 20lbs-6oz (16lbs-8oz with OTA and focuser only) this scope is ideal for use with compact and precision equatorial mounts such as the Celestron CGEM, Skywatcher EQ-6, or Orion Atlas. And with a price that’s far less than a small ED refractor or Ritchey-Chretien scope, this OTA offers an economical alternative for beginning and advanced imagers.
Fast and Precision Optics
The precisely figured 8″ f/4 primary mirror is made from BK7 optical glass for enhanced thermal stability. BK7 is far superior in thermal characteristics to soda lime float glass – the glass used in consumer products like cookware – that’s used in many reflectors in this price range. The mirror is coated with enhanced aluminum to at least 92% reflectivity and coated with a protective layer of SiO2 (quartz) for durability. The primary mirror is mounted in a cell with six external push-pull collimation knobs on the back of the tube, and the center-marked primary makes collimation with a laser a snap.
With a cropped-sensor DSLR camera or an astronomy camera such as the ZWO ASI071MC-Pro with an APS-C sensor, this scope gives a field of view across the diagonal of nearly 2 degrees, more than enough to frame the brightest regions of extended deep-sky objects like the Andromeda and Triangulum galaxies, the Orion Nebula, and the Horsehead Nebula.
Focuser and Accessories
The solid dual-speed 2″ Crayford-style linear bearing focuser handles DSLR cameras, webcams, astronomy video cams, and large sensor CCD and CMOS cameras for astrophotography. It also has a tension knob to allow you to secure heavier loads. The ridged focus knobs give you a good feel and grip, even with gloved hands in cold weather, and the 10:1 fine focus knob lets you snap your image into perfect focus. The drawtube of the focuser is engineered to have minimal wear and very little flexure with most cameras. It offers 2″ of focus travel and includes a focusing scale on the top of the drawtube to make it easy to return to the correct focus position during each observing session.
This OTA comes with a 1.25″ eyepiece adapter with compression ring so you can use cameras with 1.25″ nose pieces, and it includes a 2″ extension tube with 35mm (1.38″) extension to give you flexibility in back-focus adjustment for visual use. This instrument can also be used with 1.25″ or 2″ eyepieces for visual observations of solar system or deep sky objects. It includes a big 8×50 straight-through achromatic finder with non-illuminated crosshair.
Tube and Mounting Rings
The tube of this imaging Newtonian is made from rolled steel for good thermal stability and it’s capped with end rings of die-cut aluminum for protection and rigidity. It includes a dust cap. The scope also comes with two split-hinged die-cast aluminum mounting rings with felt lining to protect the finish of the tube. These rings make it easy to rotate the tube to bring the focuser and finder to the most comfortable viewing position. The bottoms of the rings have threaded mounting holes for a Vixen-style mounting plate (which is included) or an optional Losmandy-style plate. The tops of the two rings each have two threaded M6x25mm holes that are 7.5″ apart so you can install a separate dovetail to mount other accessories such as a guide scope.
The tube has an attractive outside gloss white finish and a matte black interior finish to reduce stray reflection and increase image contrast. The tube is 9.15″ in diameter (9.3″ at the end rings), 27.75″ long, and it extends beyond the focuser to act as a shield to prevent stray light from entering the tube and reducing image contrast. The primary mirror cell also includes a low noise, long-lifetime cooling fan powered by 8 AA batteries (batteries not included).
- Optical design: Newtonian reflector
- Aperture: 200mm (7.9″)
- Focal ratio: f/4
- Focal length: 800mm
- Primary mirror: Parabolic primary mirror; minimum 92% reflectivity; protective quartz layer
- Secondary mirror: 70mm minor axis diameter; minimum 92% reflectivity; protective quartz layer
- Secondary mirror holder: 4-vane all metal spider
- Secondary obstruction size: 35.0% by diameter; 12.3% by area
- Tube outside diameter: End rings = 9.3″; tube = 9.15″
- Tube length = 27.75″
- Tube weight (with included accessories): 20lbs-6oz
- Shipped size / weight = 34″x16.5″x14″ / 28lbs-2oz
- 200mm f/4 Newtonian optical tube assembly
- 2″ Crayford-style linear bearing focuser with 1.25″ eyepiece adapter
- 8x50mm straight-through finder with bracket and base
- Tube rings
- 13″ Vixen-style dovetail rail
- 2″ extension tube with 35mm extension
- Front dust cover