Small Refractors, Beginners, and Messier Hunting

1997 Dec 12

A recent break between storms let me finish a Messier survey in my yard in Palo Alto, California. I try the Messiers with all the telescopes and binoculars that come my way; this time -- my eighteenth -- was with an 80 mm f/11.4 Celestron refractor, made in Japan, by Vixen. It has enough oomph to chase down Messier objects from my none too dark suburban bedroom community -- I have seen M74, M76, and M33 at 32x from my yard, to mention a few considered difficult.

What remained were the galactic clusters east and southeast of Orion, brighter in principle, but often lost in the light dome of Silicon Valley and San Jose, to the south. But on this evening, rain-washed sky sparkled clear and transparent, and M41, 46, 47, 48, 50, and 93, were easy to find and easily resolved, using a 28 mm orthoscopic eyepiece for 32x. M41 was the best, to my aesthetic judgement -- its relatively small number of stars, all relatively bright, makes it particularly fine for small apertures.

There are arguments about whether small refractors make good beginner instruments. I recommend a six- or eight-inch Dobson-mounted Newtonian to newcomers past binoculars, but a good small refractor has much virtue. It will come to thermal equilibrium quickly, with little trouble from tube currents. On an altazimuth mount, it is quick to set up, too -- I dangle a pouch of eyepieces on the focuser, tuck a star atlas under an arm, and pick up the whole telescope and tripod all at once, to carry outside.

A 6- or 8-inch reflector will gather more light, and unless the seeing is really ratty, will show more detail in every kind of object. Yet an 80 mm refractor is certainly versatile. I have used this one for Messier objects, for Lunar and planetary work, and for double stars. Even though the reflector offers more performance, there is still plenty to do with a telescope such as this one.

Good small refractors are costly -- an altazimuth Vixen 80 mm runs nearly $600 from Telescope and Binocular Center (including shipping), a fair bit more than the Dobsonians I mentioned earler. Yet other 80 mm refractors sell at much lower prices. Some are made in China: I hear mixed reviews of them, but historically, China has as good a reputation for quality products as Japan, so that may change.

An 80 mm with less focal length would be nice -- more compact and less jiggly, and better for finding things and for deep-sky work. At f/8, a 32 mm Plossl in a 1.25 inch focuser would give a reasonably large exit pupil (4 mm) and a field not so narrow to be tunnel-like. Vixen makes a 102 mm f/9.8 refractor whose conventional-doublet objective shows acceptably little color; such a design should work well at 80 mm f/8. Celestron and Orion import an 80 mm f/5, but it's too fast for a general-purpose conventional doublet -- the ones I have seen have too much chromatic aberration for high-magnification work.

Jay Reynolds Freeman; 1997 Dec 12