กล้องดูดาว GSO 12" f/8 Ritchey-Chretien Telescope OTA with 3.25" Dual-speed Linear-Bearing Crayford Focuser RC12T, Carbon Fiber Truss

• กล้อง Ritchey-Chrétien เป็นกล้องระดับ Advanced เหมาะกับผู้ที่ต้องการถ่ายภาพอย่างจริงจัง และสามารถใช้ดูดาวด้วยตา (visual) ได้ด้วย โดยให้ภาพที่คมชัด
• หน้ากล้อง 12" f/8 เก็บแสงมากพอสำหรับการถ่ายภาพดวงจันทร์ ดาวเคราะห์, Deep Sky Objects (DSO) เช่น กาแลกซี่ nebula กลุ่มดาว (star clusters) ได้อย่างสว่างชัด
• เหมาะใช้งานกับ DSLRs หรือ dedicated CMOS หรือ CCD astronomy cameras
• การออกแบบ Ritchey-Chrétien แท้ โดยใช้กระจก hyperbolic (ซึ่งต่างจากกล้องทั่วไปที่ใช้กระจก sperical หรือ parabolic) ช่วยให้ได้ขอบภาพที่คมชัด ปราศจากความโค้งหรือผิดเพี้ยน (curved field) หรือดาวมีหาง (coma) หรือสีผิดเพี้ยน (false color)
• กระจกสะท้อนแสงไม่ต่ำกว่า 95% แบบ diffraction limited เคลือบ Quartz ที่ขยายต่ำเมื่ออุณภูมิเปลี่ยนแปลง มีความทนทานนับสิบปี
• การออกแบบ Carbon-fiber truss tube ลดการขยายตัวของชิ้นส่วนต่างๆ ไม่ทำให่จุดฟอกัสเปลี่ยนไปขณะถ่ายภาพ และยังเบากว่ากระบอกโลหะ
• มีครีบกันแสงสะท้อนภายในกระบอกแสง (baffle) ที่ออกแบบโดยระบบคอมพิวเตอร์ ทั้งในส่วนของกระบอกของกระจกหลักและกระจกรอง จึงให้ภาพคมชัดสูง (high contrast) โดยไม่ถูกแสงภายนอกรบกวน
• พร้อมฟอกัสเซอร์แบบ Linear-bearing Crayford 3.25" แบบหมุนได้ (rotatable) ลูกบิดล๊อกเพื่อกันอุปกรณ์ที่หนักขยับขณะถ่ายภาพ พร้อมระยะการฟอกัส (focus travel) 50มม
• Dual Speed focuser สามารถปรับฟอกัสที่ความละเอียดเพิ่มขึ้นในอัตราส่วน 10:1 เพื่อให้ได้ภาพที่ฟอกัสชัดที่สุดเท่าที่เป็นไปได้
• รวม Losmandy mounting plates และ mounting bracket สำหรับยึด optional finder scope หรือ guide scope เพิ่มเติม
• รองรับอุปกรณ์ทั้งขนาด 2" และ 1.25" มาตรฐานเช่น eyepiece, ฟิลเตอร์, barlow lens, อุปกรณ์ถ่ายภาพดาราศาสตร์แบบต่างๆ และอื่นๆอีกมากมาย
• GSO เป็นผลิตภัณฑ์คุณภาพสูง งานกลึงละเอียด ควบคุมด้วยระบบคอมฯ (CAM) ผลิตในไต้หวัน; ประกัน 2 ปี

Widely used in professional telescopes around the world, the Ritchey-Chretien (RC) design offers many advantages for serious astronomical imagers. RC scopes use primary and secondary mirrors ground to precise hyperbolic figures, which means they suffer little of the aberration and coma that plague Newtonian telescopes. They have flat fields that provide pinpoint star images right to the edge of the field of view. They do not require a corrector lens, so they have no chromatic aberration like refractors or Schmidt-Cassegrain telescopes. And they have open optical tubes, which can make it easier to come to thermal equilibrium with their surroundings.

The difficulty of figuring the optics of an RC meant that these telescopes have, in the past, been prohibitively expensive for amateur astronomers. But modern materials, design, and manufacturing techniques have enabled the production of high-quality RC scopes that are remarkably affordable.

The RC Ritchey-Chretien assemblies produced by Guan Sheng Optical (GSO) offer superb value to intermediate and advanced astronomical imagers who are looking for a longer focal length scope to use with cropped sensor and full-frame DSLR cameras, as well as nearly all dedicated astronomy cameras, including video cameras for electronically-assisted astronomy (EAA). These scopes come with precisely figured optics, baffled tubes for superior image contrast, and rugged and precise dual-speed focusers to securely hold your camera and accessories.

(NOTE: This telescope is equipped to accept 1.25” and 2” eyepieces for visual use, and it does produce acceptable visual images. However, it is primarily intended for imaging applications. Observers looking for a compact and longer focal-length OTA for visual observing should consider a Schmidt-Cassegrain or Newtonian telescope.)

Optics and Tube

This RC OTA comes with a 300mm (11.81”) mirror with a 2400mm focal length, giving it a relatively fast focal ratio of f/8 in a compact steel tube that’s only 34” long.  

The precisely figured hyperbolic primary mirror is made from quartz for enhanced thermal stability. Quartz is superior in thermal characteristics to BK7 glass or soda lime float glass - the glasses used in consumer products like cookware - that's used in many reflectors in this price range. The mirror is coated with enhanced aluminum to a nominal reflectivity of 95% and coated with a protective layer of SiO₂ (quartz) for durability.

The primary mirror is mounted in a fixed cell that’s heavily baffled to prevent stray light from reducing contrast. While Schmidt-Cassegrain telescopes come to focus by moving the position of the primary mirror, RCs scopes have a fixed primary mirror and an external focuser. This avoids image shift while focusing, a big benefit for astrophotgraphers. The rear mirror cell includes three built-in cooling fans to help equalize the temperature of the primary to ambient as quickly as possible (requires 8xAA batteries, not included).

The secondary mirror is held in a baffled cell that’s fixed to the outer tube with a 4-vane spider. The secondary cell has adjustable screws to aid in collimating the optics. The secondary mirror includes a center dot to aid in collimation.

The Serrurier truss tube components are made of a strong, light-weight carbon fiber composite material that exhibits extremely low thermal expansion to prevent changes in tube length during temperature changes. The tube design is based on two sets of opposing trusses to resist flexure as the tube orientation changes, even as it passes through the meridian. As a result, the optical elements remain in their optimum position to help achieve the sharpest possible images.

Focuser and Accessories

The solid 10:1 rotatable dual-speed 3.25” 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 and a locking 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 50mm 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.

The telescope includes two 1” and one 2” extension rings for situations when you need further backfocus, or when you want to reduce the extension of the focuser’s drawtube to minimize its deflection under heavier loads. It also comes with a 1.25"-2” adapter with compression ring so you can use cameras with 1.25" nose pieces.

To enable you to solidly and securely mount the telescope, a 14” long Losmandy D-plate is included. There’s also a "U" style base for mounting a mini guide scopes or red-dot or magnifying finders. A primary mirror dust cover and a secondary mirror dust cover are included with the telescope.

With all accessories, the total weight of the tube is 52lbs-12oz. For astronomical imaging applications, this RC scope should be paired with an equatorial mount that has sufficient capacity for this weight, along with cameras and other accessories.

What’s in the Box

• Ritchey-Chretien truss-tube optical assembly with 300mm f/8 primary mirror
• Dual speed rotatable 3.25” Crayford-style linear bearing focuser with 2" eyepiece holder and 1.25" eyepiece adapter
• Losmandy D-plates for mounting (2x)
• 1x2" and 2x1” extension rings
• "U" type finder base (finder not included)
• Front dust cover

Specifications

• Optical design: Ritchey-Chretien reflector
• Aperture: 300mm (11.81”)
• Focal ratio: f/8
• Focal length: 2400mm
• Primary mirror: Hyperbolic primary mirror with enhanced Al coating to 95% reflectivity, with protective quartz layer
• Secondary mirror: Hyperbolic with enhanced Al coating to 95% reflectivity; protective quartz layer; O.D. of secondary cell is 5.9”; center-dot for collimation
• Secondary mirror holder: 4-vane all metal spider
• Tube outside diameter = 17.3” (at middle of truss)
• Tube length = 34”
• Tube weight (with included accessories): 52lbs-12oz
• Shipped size / weight = 44”x24”x25” / 73lbs-6oz
• Warranty: 2 years

Support Documents

Manual: GSO Ritchey-Chretien Telescope Manual (by iOptron)

Note:
- User Manual is made by iOptron for their Phtron series RC telescopes. Other than cdifferent color and logo, almost all aspects of the telescope OTA and accessories are the same. 

GSO is a leader in optical telescopes and accessories and their products have been sold for years by the "Big Three" (Meade, Celestron and Orion) under their own brand names. GSO telescopes and accessories are also sold under different names world-wide; Zhumell (USA), Apertura (USA), TPO (USA), Teleskop Service (Germany), Sky Optic (France), Antares (Canada), Astronz (New Zealand), and more than a dozen more brands too many to name. GSO is known for their high consistency in quality control, low defect rate, and their Taiwanese-based manufacturing scores closer to Japan in quality than other telescope manufacturers which mostly manfacture thier scopes in Mainland China. Give these telescopes a try - you will not be disappointed!