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Posted by / 30-Aug-2017 23:50

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My second choice for an instrument intended for visual observation of the Moon would be a refractor of at least 5 inches (127mm) aperture…The Newtonian reflector is a popular choice.

Money wise, they are cost effective, and most importantly, you can obtain a large aperture telescope for a reasonable sum of money…..

If does not grudge the extra attention to keep a reflector in perfect adjustment, its performance in revealing planetary detail will equal that of a refractor of the same aperture, particularly if it is mounted with an open, lattice work tube, when a further improvement may be derived from the employment of an electric fan to keep the column of air above the mirror well mixed. A 106mm Takahashi flat field quadruplet refractor can be had, without mount, for only a little more than I paid for a high-end 12.5″ dobsonian Newtonian with state-of-the-art optics. If you buy your scopes for visual use, the Tak isn’t just over-expensive, it’s ridiculous.

Moreover it has practically negligible chromatic aberration, whereas colour estimates made with a refractor are exceedingly unreliable. If astro-imaging is your forte, the Tak will be the better choice. If you buy your scopes for photography, though, that Tak is an incredible choice.) apertures.

‘In medio stat virtus’, or, as this Latin rendition of Aristotle’s maxim has been translated into English, “All things in moderation.’The trend towards larger and larger reflectors is indeed exciting, and I can understand the need to keep them short focus( typically f/4 to f/5).

But why are so many small ones made with these focal ratios?

Pardon my bias, but shallow dish reflectors are my favorite type of telescope.

They have been amng the favorite instruments of serious planetary observers for many decades.

Those with focal ratios less than f/6 have very deeply curved mirrors, and so are referred to here as ‘deep dish’ Newtonians.

Reflectors with focal ratios of f/6 and greater will be called ‘shallow dish’ telescopes.

Such telescopes bring out the worst in the Newtonian design.

The 6 inch f/8s and 8 inch f/7s common many years ago, were much better and more versatile reflectors than many commercially available today.

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As ever, an aperture of 100 to 200mm and a focal ratio of f/4 to f/6 is most appropriate.