Astrograph telescope GSO Ritchey-Chrétien for observation and astrophotography.
Astrograph Tube TS GSO Ritchey-Chrétien PRO RC 8 Carbon
Telescope Ritchey-Chrétien with a diameter of 203mm and focal length of 1624mm, with focal ratio f/8.
Telescopes Ritchey-Chrétien (RC) are known for their fantastic optical performance, especially when focusing on photographic applications. But at the same time, telescopes Ritchey-Chrétien have also been notorious for their really high prices. In an attempt to change this dynamic, the popular manufacturer GSO (Guan Sheng Optical), widely known for its excellent Newton tubes, began manufacturing telescopes Ritchey-Chrétien.
The result of this decision has been the production of an instrument that is superior in many respects to conventional Schmidt-Cassegrain instruments and at a price that can still be considered affordable.
The Astrographer GSO Ritchey-Chrétien 8" f/8 was designed to provide an illuminated field on the 35mm format (24x36mm). For cameras with a smaller sensor, which are basically most CCD cameras, it is not even necessary to use a field flattener. For cameras with larger CCD's the use of a field flattener is recommended.
Since the Ritchey-Chrétien optical system does not require corrective lenses or plates, a clean image without false colors or chromatic aberrations is obtained. The use of IR CUT (Infrared blocking) filters is also unnecessary, thus helping to increase the amount of light captured by the instrument.
How to bring a DSLR camera to the point of focus?
The telescope GSO Ritchey-Chrétien has a generous backfocus, allowing the attachment of multiple accessories such as off-axis radial guides, filter-holder wheels, etc. If you want to take pictures with a DSLR camera working at prime focus or without intermediate accessories and without the focuser being in a very extreme position, it will be necessary to attach some spacer accessories:
- GSRCV50: 50mm spacer to be placed between the focuser and the telescope.
- TSFA240: T-adapter with 40mm extension.
General characteristics:
Optical DesignRitchey-Chrétien: Genuine Ritchey-Chrétien with hyperbolic primary and hyperbolic secondary mirror. No corrective plates or lenses in the optical train.
Optical characteristicsDiameter of 8" (203mm), focal length of 1624mm and focal ratio f/8.
Primary mirrorSurface of Quartz and with a quality of 1/12 wavelength or better. The primary has a high-reflectivity dielectric optical treatment that provides a 99% reflection coefficient.
Secondary Mirror: Quartz. The secondary mirror has a high-reflectivity dielectric optical treatment that offers a reflection coefficient of 99%. Integrated in a robust collimatable cell. The obstruction is 42.5%.
Tube: tube of carbon fiber with metallic cells to support the primary and secondary. Complete weight of 6.1 Kg.
Computer-optimized baffle systemThe inside of the tube has a series of PC-designed Baffles (partial barriers or corrugations) designed to optimize the suppression of internal reflections or residual light.
Focuser: Focuser Crayford 1:10 for extremely smooth focusing. The system of double speed 1:10 (dual speed focuser) is basic for good performance in astrophotography. It will not produce image movements (shift that is usually caused by the primary mirror) and it has a load capacity up to 5Kg!! The focuser accepts 2" and 1.25" accessories.
DovetailThe tube is fitted with a milate tail on the lower part of the tube Vixen (narrow for GP type saddles). Therefore it can go with any mount that has a head type Vixen GP.
The 2" Monorail focuser is much more than a simple Crayford
The Monorail focuser combines the ease of movement of a Crayford focuser with the rigidity of a rack and pinion focuser. Thus, astrophotography becomes a success.
♦ Solid stainless steel platen instead of small ball bearings for greater rigidity.
♦ There is no more tilt when locking the draw tube.
♦ 360° rotation for optimal object alignment.
♦ Female thread M69x1 for threaded adaptations
♦ 2" and 1.25" compression rings for push-on adaptations
♦ Dual speed 1:10 for precise focusing
♦ Motor focus can be easily adapted after the fact
♦ Lined scale for quick focus recovery.
♦ Easy handling
What is delivered with the telescope?
♦ 8" f/8" RC Astrograph
2" double speed MONORAIL focuser
♦ 2x dovetail
♦ M90 extension tubes for easy reach of the spotlight
Collimation manual
OPTICAL ADVANTAGES OF RITCHEY-CHRÉTIEN ASTROGRAPHS FROM GSO
Optical design: Ritchey-Chrétien True (True RC)
The astrographers GSO Ritchey-Chrétien are true, pure reflecting telescopes. Unlike the Maksutov or Schmidt-Cassegrain systems that have spherical mirrors and therefore need correctors, or the pure newtons that always need a coma corrector, the Ritchey-Chrétien systems are very well corrected by themselves without the use of corrector lenses and that makes them an ideal instrument for astrophotography.
RCs have a concave hyperbolic primary mirror and a convex hyperbolic secondary mirror.
The resulting image is fully corrected over the entire field while achieving an image sharpness on the optical axis far superior to that achieved with a traditional Schmidt-Cassegrain or Newton.
It is for this reason that Ritchey-Chrétien telescopes are very popular for astrophotography. The Ritchey-Chrétien configuration is the most frequently used design for professional telescopes such as the 10-meter Keck telescope in Hawaii or the VLT in Chile. Therefore, GSO puts a Ritchey-Chrétien optical design at the service of amateurs but without needing NASA's budget!!!!
Highly reflective 99% Dielectric Coating
The telescope primary mirror GSO Ritchey-Chrétien 8" is made of Quartz, which, like Zerodur, has virtually zero thermal expansion coefficient, allowing it to offer excellent optical performance as the temperature drops as the night progresses. Both the primary and secondary mirrors have a 99% reflection coefficient and are treated to protect the mirror from scratching and aging. Compared to similar instruments, more effective light collection is achieved.
Each optical kit is verified by the manufacturer
To maintain the optical quality level, each optical kit is checked and corrected by hand after leaving the automated production process. The optical equipment is then verified with a Zygo interferometer.
Summary of main technical characteristics:
The Ritchey-Chrétien 8" is the ideal telescope for astrophotography - more stable focus thanks to the carbon tube.
♦ Aperture 8" / 203 mm - focal length 1624 mm - focal ratio f/8
♦ Hyperbolic primary and secondary mirror for very high sharpness on the optical axis and a large well-corrected field for astrophotography
♦ Fused silica mirrors for stable focusing position
♦ 99% high reflectivity dielectric coating on the main and secondary mirror for an even brighter image
♦ Carbon tube: increased rigidity and better focusing stability for astrophotography
♦ Faster cooling due to open construction
♦ Level dovetail bar Losmandy at the bottom, level dovetail bar Vixen at the top
♦ High quality 2" dual speed MONORAIL focuser with 2" / 1.25" reduction adapter - Motorized focuser available as option
♦ Spacer sleeves are included for optimum focusing position behind the focuser.
RC correctors for larger sensors from APS-C upwards are optionally available.
♦ Optional: CCD47 - 0.67x focal length reduction for photography our recommendation for shorter exposure times.
Note: Some photos show the tube with black front ring. The telescope is delivered with red front ring.
Technical Specifications:
Astrograph Tube TS GSO Ritchey-Chrétien PRO RC 8 Carbon
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