GSO 12" f/5 Newtonian Reflector Telescope - Steel OTA (White) # GS930

1. Portable, Light Weight, and Economical

The GSO 300mm (approx. 12") f/5 Newtonian offers a fast focal ratio that's ideal for observing wide-field views of deep sky objects. The 1500mm focal length makes for a tube length of about 56.6". With a total weight of only 50lbs 6oz (with all included accessories) this scope is ideal for use with a heavy-duty equatorial mount. And with a price that's far less than many small ED refractors or Ritchey-Chretien scopes, 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 GS930-LRN upgraded version of this item since these telescopes have a more robust dual-speed linear-bearing Crayford focuser.

2. Full Optical and Mechanical Testing and Quality Control - An Agena Exclusive!

GSO telescopes are available from several suppliers, but Agena does much more than simply move the telescope boxes from GSO to you. Each GSO imaging Newtonian telescope at Agena undergoes a thorough physical, mechanical, and optical evaluation at our shop upon arrival - all at no extra cost to you.

Every GSO telescope is inspected to ensure good cosmetics, collimation, smooth focuser operation, and to make sure all parts are included by the manufacturer. Most importantly, we also check each telescope using a rigorous three-point on-site optical evaluation consisting of the following optical bench tests to ensure that your telescope delivers excellent optical performance:

• Foucault Test: This knife-edge test is performed at the center of curvature of the primary mirror to evaluate the quality of the mirror's conic shape.
• Ronchi Test: We then perform a Ronchi grating test at the center of curvature at inside focus, at focus, and outside focus. This is a qualitative method to evaluate primary mirror smoothness and figure.
• Star test: Finally, we collimate the complete telescope and perform an autocollimation test with an artificial star to examine the overall system's image performance at the focus point.

This testing is performed and certified by a master optician to make sure each GSO instrument sold by Agena has excellent optical performance before it ships. Each telescope should be ready to go out of the box when you receive it.

3. Fast and Precision Optics

The precisely figured 12" 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.

4. Focuser and Accessories

The solid dual-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. It includes a 8x50mm straight-through achromatic finder with non-illuminated crosshair.

5. 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. 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). 

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 13.6" in diameter (14.25" at the end rings), 56.6" long, and it extends beyond the focuser to act as a shield to prevent stray light from entering the tube and reducing image contrast.

6. What's in the Box

• 300mm f/5 Newtonian optical tube assembly
• 2" dual-speed Crayford-style focuser with 1.25" eyepiece adapter
• 8x50mm straight-through finder with bracket and base
• Tube rings
• 15.5" Losmandy-style black dovetail Plate
• 2" extension tube with 35mm extension
• Front dust cover
• No instruction manual is included

7. Specifications

• Optical design: Newtonian reflector
• Aperture: 300mm (11.8")
• Focal ratio: f/5
• Focal length: 1500mm
• Primary mirror: Parabolic primary mirror; minimum 92% reflectivity; protective quartz layer
• Secondary mirror: 88mm minor axis diameter; minimum 92% reflectivity; protective quartz layer
• Secondary mirror holder: 4-vane all metal spider
• Secondary obstruction size: 23.3% by diameter; 5.4% by area
• Tube outside diameter: End rings = 14.25"; tube = 13.6"
• Tube length = 56.6"
• Tube weight (with all included accessories): 50lbs 6oz
• Shipped size / weight = 61"x20"x20" / 68lbs-4oz
• Inspected for collimation and focuser operation at Agena AstroProducts
• Warranty: 2 years