Refractor Telescopes

An In-Depth Guide

Refractor telescopes, also known simply as refractors, are among the most iconic and historically significant instruments in astronomy. Their elegant design and ease of use have made them a favorite for both amateur and professional astronomers. This article explores the workings of refractor telescopes, their history, notable examples, and options available for consumers today.

How Refractor Telescopes Work

Refractor telescopes use lenses to gather and focus light. The primary components of a refractor telescope include:

1. Objective Lens: The large lens at the front of the telescope that collects light and bends (refracts) it to a focal point.
2. Eyepiece: The lens through which the observer views the magnified image. The eyepiece can be changed to provide different levels of magnification.
3. Tube: The body of the telescope that holds the objective lens and eyepiece in alignment.

Light enters the telescope through the objective lens, which bends the light rays to converge at a focal point. The eyepiece then magnifies this image, making distant objects appear closer and clearer. The quality of the image depends on the quality and size of the objective lens and the design of the eyepiece.

History of Refractor Telescopes

The refractor telescope was invented in the early 17th century. Key milestones in its development include:

1. Hans Lippershey: A Dutch spectacle maker, credited with creating the first practical refracting telescope in 1608.
2. Galileo Galilei: Improved upon Lippershey's design and became the first to use a telescope for astronomical observations in 1609. He discovered the moons of Jupiter, the phases of Venus, and the rough surface of the Moon.
3. Johannes Kepler: Proposed an improved design using a convex lens for the eyepiece, which allowed for a wider field of view and higher magnification.

Refractor telescopes dominated astronomical observations until the 18th century when larger reflecting telescopes began to emerge.

Examples of Historic Refractor Telescopes

1. Yerkes Observatory: Located in Wisconsin, USA, this observatory houses the largest refracting telescope ever built, with a 40-inch (1.02-meter) objective lens.
2. Lick Observatory: Situated in California, USA, it features a 36-inch (0.91-meter) refractor, which was the largest in the world when it was completed in 1888.
3. Paris Observatory: Home to the 32-inch (0.81-meter) Grand Refractor, one of the most significant refracting telescopes in Europe.

Refractor vs. Reflector Telescopes

While refractor telescopes use lenses, reflector telescopes use mirrors to collect and focus light. Reflectors, invented by Isaac Newton in the late 17th century, address some of the limitations of refractors, such as chromatic aberration (color distortion caused by lenses) and the practical difficulties of constructing very large lenses. Reflectors are generally more cost-effective for larger apertures, making them popular for both amateur and professional astronomers seeking to observe faint and distant objects.

Consumer Available Refractor Telescopes

Refractor telescopes are widely available for amateur astronomers and come in various sizes and price ranges. Some popular models include:

1. Celestron AstroMaster 70AZ: A beginner-friendly telescope with a 70mm aperture, suitable for observing the Moon, planets, and bright deep-sky objects.
2. Orion ED80T CF Triplet Apochromatic Refractor: Known for its excellent optics and color correction, this 80mm aperture telescope is ideal for astrophotography and high-quality visual observations.
3. Sky-Watcher ProED 100mm Doublet: Offers a 100mm aperture with high-quality optics and minimal chromatic aberration, making it a great choice for serious amateur astronomers.

Sky Watcher EvoStar 100 APO Doublet Refractor

• Aperture: 100mm (4")
• Focal Length: 900mm
• Focal Ratio: f/9
• Optical Design: Apochromatic Doublet
• Weight: 6.8 kg (15 lbs)
• Mount: None included (OTA only)
• Features: High-quality Schott glass, dual-speed Crayford-style focuser, comes with a carrying case.

Explore Scientific ED102 Essential Series

• Aperture: 102mm (4")
• Focal Length: 714mm
• Focal Ratio: f/7
• Optical Design: Apochromatic Triplet
• Weight: 4.6 kg (10.2 lbs)
• Mount: None included (OTA only)
• Features: Fully multi-coated optics, precision Crayford focuser, compatible with 2" accessories.

Celestron NexStar 102 SLT

• Aperture: 102mm (4")
• Focal Length: 660mm
• Focal Ratio: f/6.5
• Optical Design: Achromatic Doublet
• Weight: 6.2 kg (13.7 lbs)
• Mount: Alt-Azimuth GoTo Mount
• Features: GoTo technology with 4,000+ celestial objects, SkyAlign technology for easy alignment, fully computerized hand control.

Meade Series 6000 115mm ED Triplet APO

• Aperture: 115mm (4.5")
• Focal Length: 805mm
• Focal Ratio: f/7
• Optical Design: Apochromatic Triplet
• Weight: 7.7 kg (17 lbs)
• Mount: None included (OTA only)
• Features: FPL-53 glass, 2.5" dual-speed Rack & Pinion focuser, sliding dew shield, perfect for visual observation and astrophotography.

Stellarvue SVX152T APO Triplet

• Aperture: 152mm (6")
• Focal Length: 1216mm
• Focal Ratio: f/8
• Optical Design: Apochromatic Triplet
• Weight: 18.6 kg (41 lbs)
• Mount: None included (OTA only)
• Features: Precision-crafted lenses, heavy-duty construction, excellent color correction, designed for both visual and imaging use.

Conclusion

Refractor telescopes have a rich history and continue to be a popular choice for astronomers of all levels. Their simple, reliable design, combined with advancements in lens technology, ensures they remain a valuable tool for exploring the night sky. Whether you're a novice stargazer or an experienced observer, a refractor telescope can provide stunning views of celestial wonders.