Refractor telescopes are what the average person identifies with the word “telescope.” These consist of a long, narrow tube in which light passes in a straight line between the front, objective, lens and a rear-mounted eyepiece. Some examples of famous refractor telescopes are the 36-inch refractor at Lick Observatory on Mount Hamilton and the 40-inch refractor at Yerkes. These two telescopes are the worlds largest refractors.
- Simplicity of design contributes to ease of use and reliability;
- Require little or no maintenance;
- Excellent for lunar, planetary and binary star observing, especially in larger apertures;
- Good for distant terrestrial viewing;
- Offer high-contrast images with no secondary mirror or diagonal obstruction;
- Render good color in achromatic designs and excellent in apochromatic, fluorite and ED designs;
- Sealed optical tube reduces image-degrading air currents and protects optics,
- Have permanently mounted and aligned objective lenses.
- More expensive per inch of aperture than reflector or catadioptrics designs;
- Heavier, longer and bulkier than equivalent-aperture reflectors and catadioptrics;
- Cost and bulk factors limit the maximum practical aperture size,
- Less suited to viewing small and faint deep-sky objects because of practical aperture limitations.