Home > Astronomical Telescopes > Altair Astro > Ritchey Chrétien Astrograph Series
Model: AA8RC-CFBrand: Altair
No stock, delayed despatch
Check carefully when buying a similar looking RC telescope at a cheaper price. Always check the following accessories are included, because if they aren't, you will need to buy them separately at higher cost.2x Losmandy plates top and bottom (without which the front and rear mirror cells are not consistently supported causing uneven tilt). In our opinion and as we have discovered, the OEM extruded Vixen format bar is inadequate to support a telescope of this weight without flexure and rocking from side to side. The larger Losmandy format plate, and the radius blocks on which they are mounted are considered essential for serious imaging.3x extension tubes (2x 25mm and 1x 50mm). Without these, you will struggle to achieve focus for most CCD or DSLR imaging systems, and your telescope probably won't work without them.
Altair Astro include these items with each scope at a slightly higher price, but at an overall saving compared to buying them separately. We've had numerous requests from customers who bought these scopes without these accessories, but at this time, we're unable to provide these items separately because they're included in the box with each scope.
This is a deluxe, "fully loaded" version of the tried and tested 8" F8 Carbon Fibre Ritchey-Chrétien with the following features:
A 2" Dual Speed Linear Bearing Focuser included as standard. It will handle a DSLR or CCD camera, and a light weight filter wheel perfectly well, and is adequate in most imaging situations. Note this focuser has the Linear Bearing upgrade, and will outperform most Taiwanese dual speed focusers, both in rigidity and pulling power. It is perfectly adequate for a DSLR/CCD camera and light weight filter wheel.Or choose an Optional Genuine 2" Starlight Feather Touch dual speed focuser, in the dropdown menu below (shown in the pictures) which outperforms both the standard focuser with zero backlash, greater rigidity and more lifting power. This is intended for customers with heavier large format CCD cameras, filter wheels and off-axis guiders around 4kg.Low weight low expansion Carbon Fibre OTA, weight 7.8kg with Losmandy plates top and bottom (the all-Vixen-format plate version is 7.5kg) This is a 2kg reduction in weight compared to the metal tube version, which permits your mount to track more accurately and frees up extra carrying capacity for other accessories. The use of a carbon fibre weave composite reduces the weight of the optical tube with no loss of strength or rigidity compared to a metal tube.Losmandy format dovetail plates with radius blocks are included as standard. This increases the stability of the telescope front and back ends relative to each other for better long exposures and is in our opinion the best upgrade for this scope - now offered as standard.3x Heavy Duty Extension tubes included (2x 25mm & 1x 50mm) fitting between the focuser and the telescope. CNC Machined out of solid billet aluminium, zero flex. Once again you will need these to use the telescope. We get approached by customers who bought the scope from other retailers without these accessories all the time. Unfortunately we cannot offer them separately right now because they are included with each Altair scope as standard.Low expansion fuzed quartz optics with enhanced 96% reflective coatings and silicon dioxide (Quartz) protective overcoat *Multiple internal light baffles line the optical tube.Fast efficient cool down time compared to a normal SCT due to the open-tube design. This is the most popular upgrade scope for SCT owners who want a dedicated imaging scope without the problems associated with SCTs.This telescope is designed with a lot of backfocus to use an off axis guider, AO unit and filter wheel. Therefore, to create the most rigid imaging train possible, instead of placing extension tubes after the focuser it's best to place them between the focuser and the rear mirror cell. The 1x 50mm and 2x 25mm large diameter extension rings are included for this purpose. They are placed between the focuser and telescope and are needed to achieve focus.Dimensions: OTA length 455mm Outside diameter 230mm. Carbon fibre tube weight is 7.8kg including 2x Losmandy Plates (top and bottom) and 7.5kg with Vixen-format bars top and bottom. The central obstruction diameter is 95mm.
Advantages of RC Astrographs: This true Ritchey Chretien astrograph is completely optimised for imaging. Consider these points when choosing a dedicated imaging telescope.Aperture, long focal length, price and weight. A pure two-mirror optical system means zero colour aberration and a large aperture with high resolution compared to refractors costing many times more and weighing many times more, to gain the same resolution, whilst using a reasonably priced mount. A refractor with this focal length would cost 20x the price if not more (and more to mount it), but would offer the same angular resolution. (However it would have the advantage if being a better visual scope, and you may gain one of two field stops in focal ratio).No mirror shift. Because it has a fixed focuser and mirrors which are fixed relative to each other, primary mirror flop and the resultant image shift issues associated with SCT telescopes with moving mirrors are avoided. The spacing of the mirrors relative to each other are constant so the optical design doesn't change depending on your camera setup. There is no need for mirror locks like on an SCT, and you avoid the additional alignment and tilt problems these can create when the mirror locking mechanism is tightened down.Repeatable focusing. Because the mirrors don't have to move relative to each other to focus the telescope, everything remains in place, and the focal point doesn't change outside the tube, making it easier for you to achieve repeatable, accurate focusing time and time again with an external focuser. It is possible to automate the external focuser. These factors improve imaging considerably.Easier to mount and guide. The optical tube is very light yet very rigid and strong, minimising flex. With a weight 7.8kg of including two Losmandy Plates, this telescope is one of the lightest in it's aperture range. It can be carried by a reasonably priced EQ mount like the iOptron iEQ45 45lb capacity mount, along with a guide scope and wide field refractor. Using an EQ6 or CGEM is also possible as long as a light weight guide scope is used.Fastest cool-down time in it's class. Don't spend the whole night waiting for your scope to cool down. Closed tube telescopes with corrector plates such as Maksutovs and SCTs can take so long to cool down that they never reach ambient temperature during the whole night. The RC optical tube is an open design, minimising cool down time compared to SCTs with closed tubes, bringing the primary mirror down to ambient temperature as quickly as possible.Contrast and controlling stray light. The internal knife edge baffles and matte black interior ensure high contrast and minimize the intrusion of stray light, reducing background glare on long exposure images. You will never have to to line the interior of this instrument with "flocking paper" to improve contrast - common practise with other imaging reflectors. Because there is no large corrector plate pointing at the sky, it's very rare for condensation or dew to form on the optics and it almost never occurs. However for unusual and extremely dewy conditions, Kendrick dew control system heaters will fit the secondary mirror.Optical performance: The surfaces of the Ritchey-Chrétien primary and secondary mirrors are hyperbolic, and are carefully optimised to reduce coma, an optical aberration which results in flared stars at the edges of the photographic field in other Cassegrain designs. The Ritchey-Chrétien design was previously only available in large scale observatory optics, however, as mirror polishing techniques have advanced, they are finally available to the amateur astro photographer at a reasonable price. Further aberrations like field curvature are removed by the field corrector/flattener, available separately, and useful for large CCD sensors, or DSLR users, and is similar to those offered by other manufacturers charging up to four times the price.Price and performance for this aperture at an F8 focal length. For the aperture, resolution, and performance, this scope is simply the best value we have been able to source. We do not know of any other large aperture imaging OTA which can deliver results at this focal length which even comes close. Closed tube SCT telescopes with an F10 focal ratio usually cost about 25-30% more. Not only are you paying less money for a genuine RC telescope designed for imaging from the ground up, but you are getting a faster optical system which places less demand on mount, tracking and CCD camera due to shorter exposure times. At the same time, the long "galaxy-hunting" focal length is maintained.
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