GSO 6" f/4 Imaging Newtonian Reflector Telescope with LB Focuser - Steel OTA (White) # GS550-LRN

1. Portable, Light Weight, and Economical

The GSO 150mm (approx. 6") f/4 imaging Newtonian offers a fast focal ratio that's ideal for capturing wide-field images of hundreds of celestial objects. The short 600mm focal length keeps the tube length to a compact and easy-to-handle 21.75", making it straightforward to guide during extended exposures. With a total weight of only 13lbs-7oz (9lbs-12oz with OTA and focuser only) 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 beginning and advanced imagers. 

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 6" 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 2.6 degrees, more than enough to frame the brightest regions of extended deep-sky objects like the Andromeda Galaxy, Orion Nebula, and the Horsehead Nebula.

4. Focuser and Accessories

The solid 10:1 dual-speed 2" Crayford-style dual-speed focuser handles small to mid-sized astronomy cameras and webcams. It also has a tension knob and a locking knob to allow you to secure the cameras and accessories. 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 8x50 straight-through achromatic finder with non-illuminated crosshair.

5. 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. 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 7" in diameter (7.2" at the end rings), 21.75" long, and it extends beyond the focuser to act as a shield to prevent stray light from entering the tube and reducing image contrast.

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.

6. What's in the Box

• 150mm 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
• 8.7" Vixen-style dovetail rail
• 2" extension tube with 35mm extension
• Front dust cover
• No instruction manual is included

7. Specifications

• Optical design: Newtonian reflector
• Aperture: 150mm (5.9")
• Focal ratio: f/4
• Focal length: 600mm
• Primary mirror: Parabolic primary mirror; minimum 92% reflectivity; protective quartz layer
• Secondary mirror: 62.5mm minor axis; minimum 92% reflectivity; protective quartz layer
• Secondary mirror holder: 4-vane all metal spider
• Secondary obstruction size: 41.7% by diameter; 17.4% by area
• Tube outside diameter: End rings = 7.2"; tube = 7"
• Tube length = 21.75"
• Tube weight (with included accessories): 13lbs-7oz
• Shipped size / weight = 26"x16"x10.5" / 16lbs-13oz
• Inspected for collimation and focuser operation at Agena AstroProducts
• Warranty: 2 years