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Optics:The Questar optics are manufactured to an industrial degree of excellence; the lens and mirror raw materials are specified to be of very high standard. These are precisely ground, polished and then hand figured over time to assure that each surface has a very fine smoothness and meets its prescribed curvature. The final hand aspherizing of each matched optics set assures the Questar produces textbook diffraction patterns. The work is done in small numbers, by highly experienced professionals at the family owned firm that is the source of Questars optics since it's inception.
The corrector lens is manufactured from BK-7, a Borosilicate crown glass of high purity. The BK-7 is transparent between the near infrared to the ultraviolet portions of the spectrum, thus the telescopes are apochromatic. For increased response and extended sensitivity in the ultraviolet spectrum then we do offer an optional high grade Fused Silica in place of the BK-7. The primary mirror is available manufactured from either Pyrex or Zerodur. The optional Zerodur mirror substrate is a glass ceramic combining rigidity with thermal stability, and unlike Pyrex and other super-cooled fluids, Zerodur has a crystalline matrix with boundaries smaller than the wavelength of visible light. It will be found that Zerodur will outperform Pyrex where thermal variations are pronounced, particularly when a telescope stored in a warm evironment is taken to low temperature environments Zerodur will stabilize its image faster than Pyrex.
The Questar Solar Filters are made of precisely ground and polished optical flats, which are specially selected for thier uniform transmission and freedom from anomalies that might reduce resoltion of fine Solar surface details (faculae, sun spots, etc.). The triple metal alloy coating assures that a safe and pleasing orange-red view of the Suns disk contrasted against a stark black background is provided. These filters are mounted into machined vented cells. The Questar astronomical telescope Control Box include an integral solar filter that can easily be engaged for the finder!
Coatings:Two coating options are normally offered: either "Magnesium Fluoride" or "Broad-Band". The durable magnesium fluoride anti-reflection coatings which are applied on both surfaces of the corrector lens and aluminum reflective coatings on both mirror surfaces, overcoated with silicon monoxide for protection against the elements.
The broad-band coating option includes multi-layer dielectric coatings on both corrector lens surfaces, and Silver Very High Reflectivity Coatings on both mirror surfaces, these each with protective multi-coatings. The broad-band coatings increase light transmission in the optical system by about 20%.
Other optional coatings may be applied to extend response in certain areas of the spectrum.
Mechanics:The Questar mechanical components are of precisely made almost entirely of corrosion resistant aluminum, stainless steel; no plated metals are used. The precisely machined barrel components (tolerances better than 1/2000th inch!) help to insure the telescope optics are well protected and function as close as is pracical to their theoretical limits. Where surfaces bear upon one another, materials such as phosphor bronze may be found. The phospohor bronze bushing for the precisely ground and honed stainless steel focus control rod will survive tens of thousands of rotations! Indeed we have seen numerous instances of Questars come in for service after exposure to neglect and the elements, and while the exteriors may show the wear and tear - generally we find the controls on the telescope remain crisp and function precisely; the focus of a Questar 30 years old (or more) may respond to one brushing a finger across its handle feel just as easily and smooth as that of a new instrument.
The baffling design and placement assure that Questars do not need a lens shade to protect the system from off axis lighting which might otherwise result in ghost images or flare! The "lens shade" furnished with a Questar is merely shield to protect the corrector lens against dew.
Finish:All exposed metal surfaces are lacquered, anodized or highly polished aluminum or stainless steel. Questar employs no plated metals. The base and forks of the equatorial mount are finely machined and polished to a gloss finish. Some industrial products are offered in painted finishes.
Selections:Available optional mechanical and optical design features and functions include:
Substitutions:As each instrument is essentially (and should be) made to order, there are several options available which will enhance the value and enjoyment of your telescope; we suggest that you consider these at the time of purchase as it may not be cost effective to upgrade after assembly.
A Full Aperture 89mm diameter Solar Filter may be substituted for the included 30mm diameter Off-axis Solar Filter on the Standard and Duplex models. Full Aperture 180mm diameter and 90mm diameter Off-axis Solar Filters are available for the Questar 7 telescopes.
A hand-sewn leather Deluxe Carrying Case incorporating combination locks may be substituted for the standard Vinyl Case with key locks provided with the Standard and Duplex models.
The internal 9 Volt battery powered "Powerguide II" drive and control system may be substituted for the AC synchronous clock drive in the Standard or Duplex fork mount drive base at the time of purchase or as a factory retrofit. The retrofit is also available for the or Questar 7 fork mount (which was last sold in 1994). This option is described in detail in our article of advice to those interested in selecting a Questar telescope.
Questar telescopes are American engineered, made, and assembled to provide a lifetime of service.
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