Telescope wish-list – 8″

Beyond the starter sizes of astronomical telescopes, keen amateur astronomers usually yearn for something bigger.
The ‘something bigger’ often takes the form of the popular 200mm (8″) size.
At this size there is some shake-out of the options available, as the refractors are long and heavy, and price themselves out of the running except for enthusiasts with deep pockets.

On the other end of the scale, you can get a Newtonian 200mm, on a Dubsonian mount, for under £300, cheap enough to tempt the unwary beginner. The Dobsonian mount was designed to be cheap, light and portable, for mounting large Newtonians and taking them out to astromeets and dark-sky sites, and designed to be easy to make as a DIY project. It is not really intended for starter-scopes. No single-axis tracking, no slow motions, no powered drives and no Goto.

For a Newtonian mounted on a solid equatorial mounting with electric drives and Goto, you can triple the above price.
The advantages of a Newtonian are cheapness and (usually) a short focal ratio good for astro-photography. That’s it.
Disadvantages: needs frequent collimation checks, awkward eyepiece position, requires eyepieces designed for short-focus telescopes.

Further up the scale are the catadioptric telescopes, usually a SCT (Schmidt-Cassegrain Telescope) in this size range. These have a folded optical train and a corrector plate at the front, giving a compact tube and a convenient eyepiece position, with a long focal ratio. They do not require frequent checking or adjustment. With a Goto mounting, they cost from around £1300. Good for astro-photography and general viewing (except wide-field). If you want the very best, you can spend £10,000 on a superb and fully equipped catadioptric 8″ telescope and mounting. Not that many people do, other than university astronomers.

A Goto mount will allow you to rapidly find objects by their RA and declination, something that setting circles are supposed to do but actually don’t, except at an observatory. Also they can be hooked up to a laptop for sundry purposes including accessing observing lists from the Internet.
Norton’s Star Atlas and Goto firmware databases contain small lists, but download a full list of what double stars your telescope should be able to resolve, and you’ll be gobsmacked.