Portable, Light Weight, and Economical
The GSO 150mm (approx. 6″) f/5 Newtonian offers a fast focal ratio that’s ideal for observing wide-field views of deep sky objects. The short 750mm focal length keeps the tube length to a compact and easy-to-handle 26.5″. With a total weight of only 13lbs (with all included accessories) this scope is ideal for use with compact and precision equatorial mounts such as the Celestron AVX, Skywatcher HEQ-5, or Orion Sirius. And with a price that’s far less than a small ED refractor or Ritchey-Chretien scope, this OTA offers an economical alternative for imagers and visual observers on a budget who want a larger aperture.
While this scope has a smaller field of view than a faster f/4 Newtonian, it exhibits less coma and field curvature, especially when used for visual observing with long focal-length eyepieces or small cameras. However, serious imagers with larger DSLR or astronomy cameras may wish to consider a GSO f/4 Imaging Newtonian or the GS500-LRN upgraded version of this item since these telescopes have a more robust dual-speed linear-bearing Crayford focuser.
Fast and Precision Optics
The precisely figured 6″ f/5 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.
Focuser and Accessories
The solid single-speed 2″ Crayford-style focuser handles nearly any eyepiece or lightweight camera. 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. The drawtube of the focuser is engineered to have minimal wear and very little flexure. It offers 40mm 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 a compression ring to match 1.25″ eyepieces and accessories, and it includes a 35mm-long 2″ extension tube to let you achieve focus with a 1.25″ or 2″ eyepiece when using the telescope for visual use.
Tube and Mounting Rings
The tube of this 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 to protect the finish of the tube. The bottoms of the rings have threaded mounting holes for a Vixen-style mounting plate (which is included).
The tube also has an attractive outside gloss white finish and a matte black interior finish to reduce stray reflection and increase image contrast. The tube is 7″ in diameter (7.2″ at the end rings), 26.5″ long, and it extends beyond the focuser to act as a shield to prevent stray light from entering the tube and reducing image contrast.
Please note: The tube rings included with GSO’s 6″ scopes are a bit smaller than they ideally should be. Hence, do not attempt to rotate the tube within loosened rings unless you completely open them or you will scratch the tube finish. Some customers resort to removing the felt lining and replacing it with a thinner alternative to allow the tube to rotate within the rings.
- Optical design: Newtonian reflector
- Aperture: 150mm (5.9″)
- Focal ratio: f/5
- Focal length: 750mm
- Primary mirror: Parabolic primary mirror; minimum 92% reflectivity; protective quartz layer
- Secondary mirror: 50mm minor axis; minimum 92% reflectivity; protective quartz layer
- Secondary mirror holder: 4-vane all metal spider
- Secondary obstruction size: 33.3% by diameter; 11.1% by area
- Tube outside diameter: End rings = 7.1″; tube = 6.75″
- Tube length = 26.5″
- Tube weight (with all included accessories): 13lbs
- Shipped size / weight = 30″x12″x11″ / 16lbs-6oz
What’s in the Box
- 150mm f/5 Newtonian optical tube assembly
- 2″ single speed Crayford-style focuser with 1.25″ eyepiece adapter
- Vixen-style finder dovetail base (bracket/finder not included)
- Tube rings
- 13″ Vixen-style dovetail rail
- 2″ extension tube with 35mm extension
- Front dust cover
- 6x30mm straight-through finder with bracket