Summary
Highlights
There are three primary types of telescopes: refractors, which use lenses; reflectors, which use mirrors; and catadioptric or compound scopes, which combine both. While specific terms like 'Dobsonian' or 'Schmidt-Cassegrain' exist, they are often variants of these basic types.
Refracting telescopes use lenses to focus light and are typically long and thin. They are generally smaller and more portable. A key consideration for refractors is chromatic aberration or 'color fringing' at high magnifications, especially in doublet refractors, though triplet refractors are designed to mitigate this. They are known for being sturdy and low-maintenance.
Reflecting telescopes use mirrors to focus light, often resulting in shorter optical tubes. They are generally more affordable for larger apertures compared to refractors and are not susceptible to color fringing. Dobsonians, a type of reflector, offer great value with larger apertures and easy-to-use mounts. A downside is that the image appears upside down, requiring a finder scope, and they need occasional collimation to align the mirrors.
Catadioptric or compound telescopes combine both lenses and mirrors, making them very compact and portable, even for large apertures. This design is achieved through corrector plates and curved secondary mirrors that fold and magnify the light path internally. Like reflectors, they require collimation, but far less frequently. Their small size and portability make them a convenient option for both beginners and experienced astronomers.
When choosing a telescope, consider the largest scope you can reasonably afford and carry. For observing the moon and planets on a budget, a small refractor is a good choice. For deep-sky observing of galaxies and nebulae, a large reflector is recommended. For maximum flexibility in viewing, a Schmidt-Cassegrain or other compound telescope offers many options. Weighing benefits, considerations, and budget will help you select the best scope for your needs.