Portable, Light Weight, and Economical

The GSO 250mm (approx. 10") f/4 imaging Newtonian offers a fast focal ratio that's ideal for capturing wide-field images of hundreds of celestial objects. The 1,000mm focal length keeps the tube length to a farily compact 32.6", making it easier to guide during extended exposures. It has a total weight of 36lbs (34lbs-6oz with OTA and focuser only). And with a price that's less than many ED refractors or Ritchey-Chretien scopes, this OTA offers an economical alternative for beginning and advanced imagers.

Fast and Precision Optics

The precisely figured 10" 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 wide field of view, 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 3.25" Crayford-style linear bearing focuser with 2" eyepiece holder 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 8x50 straight-through achromatic finder with non-illuminated crosshair.

Tube and Mounting Rings

This imaging Newtonian uses a truss tube made from carbon-fiber struts and CNC-machined stainless steel and aluminum hardware for good thermal stability. The tube includes two Losmandy-style plates for mounting on a solid equatorial mount and for accessories such as guides scopes. The tube is 15.25" in diameter and 36.2" long. The primary mirror cell also includes three long-lifetime cooling fans powered by 8 AA batteries (not included). Both the primary and diagonal mirrors include built-in light shields to block stray light and improve image contrast. The scope includes a cap for the primary mirror.

What's in the Box

• 250mm f/4 Newtonian optical tube assembly
• 3.25" Crayford-style linear bearing focuser with 2" eyepiece holder and 1.25" eyepiece adapter
• 8x50mm straight-through finder with bracket and base
• Carbon-fiber truss trube
• Two Losmandy-style dovetail rails
• 2" extension tube with 35mm extension
• Primary mirror cap

Specifications

• Optical design: Newtonian reflector
• Aperture: 250mm (9.8")
• Focal ratio: f/4
• Focal length: 1,000mm
• Primary mirror: Parabolic primary mirror; minimum 92% reflectivity; protective quartz layer
• Secondary mirror: Minimum 92% reflectivity; protective quartz layer
• Secondary mirror holder: 4-vane all metal spider
• Tube outside diameter: 15.25"
• Tube length = 32.6"
• Tube weight (with included accessories): 36lbs
• Shipped size / weight = 38"x22"x21" / 49lbs-4oz
• Warranty: 2 years