Refractor telescopes are what the average person identifies with the word “telescope”. They consist of a long tube using lenses at the top of the scope directing light to the eyepiece at the bottom. This is the same basic design as a pair of binoculars. Because of the simplicity of the design makes them easy to use, maintenace free, and reliable. There are some 100 yr old refractors still in professional use today.
The refractor telescope is well suited for lunar, planetary and binary star observing, as well as distant terrestrial viewing. Refractors also have the highest percentage of the light gathered by the scope (light transmission) that actually reaches your eye. Refractors can transmit 90% or more of the light they collect, compared with the 80% transmission of reflectors and 70% of catadioptrics. That being said, refractors are more expensive per inch of aperture than reflector or catadioptrics designs. A refractors the practical apeture size is limited by cost and bulk factors. The refractor telescope needs to be heavier, longer, bulkier that similar size reflector and catadioptrics. As a result a premium 4″ apochromatic refractor typically costs and weighs four to eight times as much as a 4.5″ reflector or 3.5″ catadioptric.
With the exception of very expensive apochromatic designs, all refractor telescopes suffer from chromatic aberration (or “spurious color”). This is an optical defect that produces a faint, and normally unobjectionable, pale violet halo around bright stars, the limb of the Moon, and the planets. Chromatic aberration becomes more visible as the aperture increases and the focal ratio decreases, although modern optical systems minimize the problem in two-element achromatic refractors – and virtually eliminate it in three to four lens apochromatic systems.
While the smaller sizes are generally light and relatively cheap, refractors become more expensive and heavier than reflectors or catadioptric scopes as apertures hit 4″ (102mm) and above. A premium 4″ apochromatic refractor typically costs and weighs four to eight times as much as a 4.5″ reflector or 3.5″ Maksutov-Cassegrain. These drawbacks aside, the clarity, contrast, and sheer image quality of a good refractor is well worth your consideration.
The following chart was borrowed from an article called Why buy a reflector? at Astronomics.com. An excellent place to research and Buy a Telescope. Refractor Telescope report card ratings are based on telescope being used in excellent seeing conditions and with no light pollution. The data was a adapted from Astronomy Magazine.
E = excellent; VG = very good; G = good; F = fair; P = poor.
Advantages:
- 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
Disadvantages:
- 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.
- Suffer from chromatic aberration (or “spurious color”) in lower end scopes
Below is a breakdown of advantages, disadvantages, and performance ratings of refractor telescopes to help in your decision making. The information is borrowed from an article called Why buy a refractor? at Astronomics.com. An excellent place to go and do research and Buy a Telescope. Refractor report card ratings are based on a telescope being used in excellent viewing conditions and with no light pollution. The data was a 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:
- Performance on comets: P
- Performance on double stars: P
- Performance on galaxies and nebulas: P
- Performance on planets: P
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 (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
Refractor Telescope Recommendations
