A Buyer's and User's Guide to Astronomical Telescopes & by James Mullaney

By James Mullaney

This is often a very good publication for me. i'm studying approximately astronomy/stargazing, and in addition searching for suggestion in terms of buying my first telescope. The ebook is drastically supporting me to higher decide upon my first telescope. The publication additionally contains information regarding components for telescopes and binoculars, it additionally comprises rather a lot of knowledge on astronomy. i'm completely satisfied that i bought this booklet.

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Read Online or Download A Buyer's and User's Guide to Astronomical Telescopes & Binoculars (Patrick Moore's Practical Astronomy Series) PDF

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Additional resources for A Buyer's and User's Guide to Astronomical Telescopes & Binoculars (Patrick Moore's Practical Astronomy Series)

Sample text

E. black), which preserves the eye’s dark adaptation just as reading star charts with a red light does. ) Ritchey–Chrétien In an effort to improve the imaging quality of the classical Cassegrain reflector for photographic work, George Ritchey and Henri Chrétien jointly developed a marvelous new system in the early 1900s known as the Ritchey–Chrétien. Typically operating at effective focal ratios of f/8 or f/9, its hyperbolic primary and secondary mirrors give it both a larger and a flatter field than that of an ordinary Cassegrain, with total freedom from coma.

Another source is DGM, which offers models ranging from 4- to 9-inch in aperture, with focal ratios averaging around f/10. Their optical arrangement is similar to Orion’s, but with the secondary mirror mounted off-axis right under the focuser itself rather than across the tube from it. Prices here range from below $1,000 to over $3,000. Off-axis, unobstructed telescopes offer observers refractorlike performance with the color fidelity of a reflector – but at a significantly higher cost than for a basic Newtonian of similar aperture.

Initial versions used a single objective lens to collect and focus the image and a simple eyepiece to magnify it. Single lenses by their very nature have a number of optical shortcomings, chief among these being chromatic (or color) aberration. This results in light of different colors coming to focus at different points, producing imagedegrading prismatic haloes appearing around the Moon, planets, and brighter stars. Another serious problem is that of spherical aberration – the inability of a single lens to bring all light rays to the same focus.

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