This site describes the features of the Newtonian, one of the simplest and cheapest instruments made for astronomy.

I admit I'm partial to this inexpensive and capable design. Given its capabilities versus its price, it provides the best overall seeing for the dollar.

My 6 inch f/5, reviewed here is overall my favorite telescope. It's a good general purpose work horse. Portable, great for wide star views, and capable of delivering decent planetary images.

The Newtonian Reflector Design

After the refractor, the next telescope design that came along was the Newtonian, named after, you guessed it, Isaac Newton. This design uses a parabolic curved mirror (left side of picture) for the objective instead of a lens.

Shown: A Discovery 6 inch Equatorial

Since all wavelengths of light reflect off of a surface in the same way, the reflecting telescope is not plagued with the color problems of the refractor. The only trouble with the old reflectors was that the mirrors of the day were made of speculum metal. It provided a smooth reflecting surface, but one whose reflectivity deteriorated rapidly. So a given diameter reflector would provide much dimmer images than the same sized refractor.

That's not nearly as true today. Most mirrors of today are made of glass with a thin aluminum coating. Aluminum is very reflective, above 90%. So today's reflectors are good performers. The parabolic curve is necessary, especially in focal ratios less than f/10, in order to cause light striking the entire mirror surface to be focused to the same point.

The features that compromise the design are less to do with observing and more to do with maintenance. Newtonians expose all optical components to the elements when used. So delicate first-surface mirrors occasionally must be cleaned, and this takes care. To be cleaned, they must be removed from the telescope. This means a complete realignment of the optics will have to be performed when all elements are reassembled. In fact, alignment tweaking needs to be done routinely for best performance. Once learned, this is not a difficult procedure, but a number of observers would rather avoid this issue.

If you don't mind learning how to carefully clean your optics and realign them, a Newtonian is a good choice. I've been using Newtonians since I was about 16, so it's not a big deal. I've owned a number of them, and find them my personal favorite for an overall telescope.

I've owned a number of Newtonians over the years, some in the Dobsonian configuration. My first was a Gilbert 2.5" Newtonian -- anyone else ever have one of those? Then I obtained a 6" f/12 in sort of a kit, I had to assemble it. It was great, but so long I had to use a small step ladder to look through it much of the time.

Then I decided to make one of my own -- from scratch. Allyn J. Thompson's book Making Your Own Telescope gave me the inspiration, and the guidance of what to build. I was first thinking an 8", but Allyn stated that the perfect match to a 6" f/12 was a 6" Richest Field Telescope (RFT). That was it, I went for a 6" f/4.5. It turns out that short focus telescopes aren't the easiest to build, but I managed it. So for a time there, I had a great combination. Then I got aperture fever, going to an 8", then a 10" behemoth. In the fray I sold my 6 inchers.