The Refractor, also known as the dioptrics, is a telescope that uses lenses to refract, (bend), the light that it collects. This refraction causes parallel light rays that converge at a focal point at the opposite end, where they can be magnified by an eyepiece. The large lens at the front is called the objective lens. The objective lens usually comprises of two or more individual lenses that are bonded and or arranged together to make up what is called the objective lens cell. The glass material used can also vary which will help in the overall performance of the objective lens.



Advantages

Little or no maintenance and is easy to use.
Reliable due to the simplicity of design.
Excellent for lunar, planetary or binary star viewing.
Good for terrestrial viewing.
High contrast images due to its clear aperture (no central obstruction).
Good colour correction in achromatic designs and excellent in apochromatic, fluorite and ED designs.
Sealed optical tube reduces image degrading air currents and protects the optics.
Objective lens is usually permanently mounted and aligned.

Disadvantages

Usually more expensive per inch of aperture than Newtonians or Catadioptrics.
Heavier, longer and bulkier than equivalent aperture Newtonians or Catadioptrics.
The cost and bulk factors usually limit the maximum size to smaller apertures.
Less suited for observation of deep sky objects such as distant galaxies and nebulae because of practical aperture limitations.
Some colour aberration in achromatic designs (doublet).
Poor reputation due to low quality imported toy telescopes; a reputation unjustified when dealing with a quality refractor from a reputable manufacturer.