LENS OR MIRROR?
The choice of serious but budget-minded skywatchers is usually a Newtonian reflector, a design relatively unchanged since Isaac Newton invented it in 1668. As a rule, reflectors provide much greater aperture for the money than refractors do, and an economical 4 or 4.5 inch (100 or 110mm) Newtonian can serve as a good starter scope. Several manufacturers now offer very affordable 6 inch (150 mm) reflectors on simple Dobsonian mounts.
These provide views of planets and deep-sky targets so superior to those in smaller telescopes that it is worth making the jump up. The main drawback of a Newtonian reflector is that it requires some maintenance— the exposed and delicate mirrors need occasional cleaning and collimation.
Small refractors—in 2.4 inch (60 mm), 3.1 inch (80 mm), and 3.5 inch (90 mm) sizes— are also popular starter scopes.
These rugged, maintenance-free instruments offer crisp images and are easy to aim.
They can double for daytime activities, such as birding.
In larger sizes, retractors are premium instruments—a
4 inch (100 mm) refractor can cost five times as much as a
4 inch reflector. They often feature apochromatic (color-free) lenses, and are popular with optical connoisseurs and avid astrophotographers who prize their ultra-sharp images.