![]() Similar designs using convex secondary mirrors have been found in the Bonaventura Cavalieri's 1632 writings describing burning mirrors and Marin Mersenne's 1636 writings describing telescope designs. The Cassegrain reflector is named after a published reflecting telescope design that appeared in the ApJournal des sçavans which has been attributed to Laurent Cassegrain. Modern variants may have a hyperbolic primary for increased performance (for example, the Ritchey–Chrétien design) and either or both mirrors may be spherical or elliptical for ease of manufacturing. The classic Cassegrain configuration uses a parabolic reflector as the primary while the secondary mirror is hyperbolic. In an asymmetrical Cassegrain, the mirror(s) may be tilted to avoid obscuration of the primary or to avoid the need for a hole in the primary mirror (or both). Alternatively, as in many radio telescopes, the final focus may be in front of the primary. In a symmetrical Cassegrain both mirrors are aligned about the optical axis, and the primary mirror usually contains a hole in the center, thus permitting the light to reach an eyepiece, a camera, or an image sensor. This design puts the focal point at a convenient location behind the primary mirror and the convex secondary adds a telephoto effect creating a much longer focal length in a mechanically short system. The Cassegrain reflector is a combination of a primary concave mirror and a secondary convex mirror, often used in optical telescopes and radio antennas, the main characteristic being that the optical path folds back onto itself, relative to the optical system's primary mirror entrance aperture. Weighs 33 lbs., 12 oz.Combination of concave and convex mirrors Light path in a Cassegrain reflecting telescope Backfocus distance is 92.4mm from the 2" drawtube collar. ![]() As with any fast Newtonian, a coma corrector (sold separately) is recommended to achieve flat-field imaging performance. ![]() A 2" extension adapter (35mm length) is included for visual observation.Īdditional standard accessories include two cast aluminum tube rings, an 8x50 crosshair finder scope, and dust cap. The focuser's 2" collar accepts 2" accessories and comes with a 1.25" eyepiece adapter, both with non-marring compression ring clamps. A steel reinforcing plate directly under the focuser eliminates flexure between it and the tube. The machined 3" dual-speed (10:1) Crayford focuser boasts a linear bearing design, which adds rigidity to the drawtube to support heavier imaging loads. The mirror is center marked to aid in precise collimation, and a quick-collimation cap is included. The rear cell features large collimation knobs and a built-in fan to speed cooling of the mirror (requires 8 AA batteries, not included). The 88mm minor axis secondary mirror provides excellent full-field illumination with modern cameras, with minimal light drop-off at the edge of APS-C sized sensors. The 1000mm focal length is ideal for framing a wide variety of celestial targets! The enhanced aluminum mirror finish has 92% to 95% reflectivity and is coated with a protective layer of SiO2 (quartz). ![]() The 10" f/4 Newtonian Reflector Astrograph's 250mm (9.8") parabolic primary mirror is made of low-thermal-expansion BK7 glass, which is superior to standard soda-lime glass. Relative to premium refractors of even half its aperture, this 10" scope's affordable price makes it a terrific value. This imaging powerhouse reveals dim objects as astonishingly bright with just minimal exposure times of your DSLR or astronomical camera. For the serious astrophotographer seeking a fast astrograph with immense light-gathering prowess, the Orion 10" Newtonian Reflector Astrograph is an all-around excellent choice.
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