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Refractors—the Ultimate Imaging Instruments In a given aperture size, refractors will always exhibit sharper images than other optical designs because the refractor concentrates more light into the central airy-disk and first diffraction rings. There is no diffraction pattern interference caused by a diagonal mirror, or secondary mirror being suspended in the optical path (central obstruction) as is the case with reflector optical designs. Sky-Watcher ED-APO’s—the Ultimate Refractors Sky-Watcher ED-APO refractors provide the finest images obtainable—bar none—in their design class. If you are on a quest for the ultimate in pristine, near textbook-perfect astronomical imaging, look no further! Sky-Watcher ED apochromatic refractors deliver dramatic coal-back skies and faithful, contrast-rich views of planetary and deep-space phenomenon that are second to none. Sky-Watcher ED-APO refractors are the logical choice as an investment in advanced instrumentation for exceptional viewing or photography. Virtually Eliminates Residual Chromatic Aberration The Sky-Watcher ED-APO design assures virtual elimination of secondary, residual “false color” normally present in 2-element achromatic lens designs using Crown and Flint glass. Sky-Watcher APO refractors utilize a second lens element made from the mineral fluorite instead of Flint glass. Fluorite, CaF2, is a halide with unique properties and a hardness of only four. It is an exotic and difficult material to fabricate into a lens. Hence the cost of manufacturing a fluorite lens is quite high compared to a Flint lens element, for instance. Why fluorite? Fluorite’s molecular properties have several distinct advantages. First, it has superior dispersion characteristics compared to pure silica-based glass. It functions as a high-index lens with very low dispersion. We use the term ED to signify “Extra-low Dispersion”. Fluorite also corrects well for spherical aberration. Sky-Watcher utilizes only the very finest available fluorite lens, FPL-53. Schott Glass Used in Selected Models for Crown Element Select models of ED-APO refractors will benefit from the inclusion of Schott glass being used for the positive front Crown element in the objective. Schott is the recognized world leader in glass utilized for precision optical lens systems, including medical instrumentation, and famous-brand camera lenses. While Schott glass is only used in selected models, all other models utilize top-quality, Grade-A glass from perhaps less famous but, nonetheless, highly respected, high-quality glass manufacturers. Pride and Perfection in Optical Manufacturing Every lens element is individually inspected for purity and absence of striae and other image-degrading imperfections. Every lens is pitched polished to exacting standards of optical fabrication and performance by highly skilled opticians utilizing state-of-the-art methodology and rigidly controlled optical testing procedures. The result is high-quality, diffraction-limited optics performing to the theoretical limits of their respective aperture sizes. All lenses are uniformly air-spaced in their cell housings. Metallic High-Transmission Lens Coatings Each air-to-glass lens surface has exotic anti-reflection metallic coatings applied to ensure optimum light through-put. The proprietary Sky-Watcher “Metallic High-Transmission Coatings” (MHC) are the finest photon anti-rejection coatings in their class. Light-Baffled Optical Systems The objective lens cell is light-baffled to reject stray, unfocused light. The draw tube is likewise baffled to insure optimum contrast. The tube interior is flat blackened to help prevent unfocused internal light reflections from reaching the focal plane. Precision 2” Crayford-style Focuser is Standard Optical focus is achieved by means of a mechanically ultra-smooth, backlash-free, precision 2” Crayford-style rack & pinion focuser-assembly. The focuser offers 2 speeds for fine and ultra-fine focusing adjustments. Tube Materials The optical tube material is aluminum, powder-coated reflective gloss black with gold fleck accent. The front and back cells are cast-aluminum painted white, or black. Telescope Tube Attachment Hardware: The Sky-Watcher APO optical tubes come with attachment hardware that allows them to be securely fastened to the SW EQ5P mount, or in the case of Equinox a photo tripod or similar threaded mounting system. The quick-release tube rings provided with SW ED-APO models 80ED 100ED and 120ED are cast-aluminum, painted white. Included Components for Selected Models All SW ED-APO and Equinox ED models are supplied with 2-speed backlash-free 2” Crayford-style focusers and quality foam-lined metal carrying cases as standard equipment. SW PRO ED-APO models are also supplied with RA 8x50mm viewfinder with bracket; 2” dielectric diagonal; two 1.25” LE (Long Eye Relief) eyepieces (LE20mm and LE5mm); 1.25” focuser adaptor; and tube ring attachment hardware for mounting to the Sky-Watcher EQ5PRO Mount, or other compatible mounts. Equinox models are provided as astrographics without optical accessories, but include a foam lined carry case. The Equinox models can be used optically with optional accessories. |
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