Refractors (also known as dioptrics) are what the average person identifies with the word "telescope", a long, thin tube where light passes in a straight line from the front objective lens directly to the eyepiece at the opposite end of the tube.

For observing the Moon and major planets and separating out binary stars—a small, quality achromatic refractor of 60mm to 80mm aperture will make a fine starter scope. They are portable, maintenance free, and inexpensive ($100 - $400). Moving up to a 90mm or 100mm aperture will snare more objects and provide better performance, for a higher price. Renowned for their crisp, sharp, contrasty images—refractors are the priciest per inch of aperture of all the scopes. Their cost and bulk factors limit the practical useful maximum size to smaller apertures.

A refractor is the scope of choice if you will be doing most of your observing from the city or suburbs, where the night skies are moderately light-polluted. Here, more aperture doesn't gain you much, since viewing is restricted to the Moon and planets. A big scope would only amplify the skyglow, yielding poor washed out images.

Advantages:

• Easy to use and reliable due to the simplicity of design.
• Little or no maintenance.
• Excellent for lunar, planetary and binary star observing especially in larger apertures.
• Good for distant terrestrial viewing.
• High contrast images with no secondary mirror or diagonal obstruction.
• Color correction is good in achromatic designs and excellent in apochromatic, fluorite, and ED designs.
• Sealed optical tube reduces image degrading air currents and protects optics.
• Objective lens is permanently mounted and aligned.

Disadvantages:

• More expensive per inch of aperture than Newtonians or Catadioptrics.
• Heavier, longer and bulkier than equivalent aperture Newtonians and catadioptrics.
• The cost and bulk factors limit the practical useful maximum size objective to small apertures
• Less suited for viewing small and faint deep sky objects such as distant galaxies and nebulae because of practical aperture limitations.
• Focal ratios are usually long (f/11 or slower) making photography of deep sky objects more difficult.
• Some color 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.

REFRACTOR REPORT CARDS
(used in excellent seeing conditions and with no light pollution; adapted from Astronomy Magazine):

E = excellent; VG = very good; G = good; F = fair; P = poor.

Small aperture (2" to 3") "toy store/bargain" refractors:
Price range: $100-$200
Portability: E
Ease of setup: E
Ease of use: F
Performance on the Moon: F
Performance on comets: P
Performance on double stars: P
Performance on galaxies and nebulas: P
Performance on planets: P

Small aperture (3" to 4") achromatic refractors:
Price range: $200-$800
Portability: E
Ease of setup: G
Ease of use: G
Performance on the Moon: E
Performance on comets: F
Performance on double stars: VG
Performance on galaxies and nebulas: F
Performance on planets: VG

Medium aperture (4" to 5") apochromatic refractors:
Price range: $700-$10,000
Portability: VG
Ease of setup: E
Ease of use: VG
Performance on the Moon: E
Performance on comets: VG
Performance on double stars: VG
Performance on galaxies and nebulas: G
Performance on planets: VG

Large aperture (5" to 8") achromatic refractors:
Price range: $800-$3200
Portability: F to VG
Ease of setup: G+
Ease of use: VG
Performance on the Moon: E
Performance on comets: VG
Performance on double stars: E
Performance on galaxies and nebulas: G
Performance on planets: E

Large aperture (6" to 8") apochromatic refractors:
Price range: $5000-$27,000 and up
Portability: F
Ease of setup: F
Ease of use: VG
Performance on the Moon: E
Performance on comets: VG
Performance on double stars: E
Performance on galaxies and nebulas: G
Performance on planets: E