![]() Here’s another real-world example – notice how the telescope’s optical tube is open vs. Telescope shown: Orion SpaceProbe 130ST ( See it on ) It’s towards the top of the telescope, because that’s the location of the secondary mirror. This one also sits on a German equatorial mount. Here’s a real-world example of a reflector telescope – this is the same one sketched in the image above. But the one thing they all have in common is that they utilize a large primary mirror as the aperture of the telescope (its main light-collecting component). These include the classic Newtonian telescope (named after Isaac Newton), Dobsonian telescopes, compound or catadioptric telescopes (like the Schmidt-Cassegrain telescope which is a popular compound reflector), and more. Reflector telescopes have many sub-types which differ from each other in the number of mirrors, shape of mirrors, and other details. This makes it possible to build telescopes that can collect a lot more light without the dramatic increase in cost. As you move towards larger aperture sizes, mirrors are much less expensive to manufacture than high-quality glass lenses. This has some key advantages and disadvantages which we’ll discuss throughout this article – but there is one advantage worth pointing out right up front. This primary mirror (whose diameter is the size of the telescope’s aperture) plays the role of bouncing light rays back towards one or more additional mirrors, until the light eventually exits the telescope through the eyepiece. Unlike refracting telescopes, reflectors do not utilize a glass objective lens – instead, a large curved mirror is situated at the base of the telescope. Reflecting telescopes introduced a new concept – using mirrors as the primary way to gather light and redirect it to a focal point. Telescope shown: Orion Observer II 70mm ( See it on ) Reflector Telescopes Came Along Later, Introducing Newton’s Innovative Mirror-Based Design Image Credit: Orion (Used with Permission) Both have a 90-degree diagonal, which redirects the light upwards to the eyepiece. This one sits on an alt-azimuth mount, while the sketch above shows a German equatorial mount. Here’s a real-world example of a refractor telescope – this is similar to the one sketched in the image above. Refractors come in many varieties – and they can be optimized for a variety of usage scenarios including astrophotography, research, and visual astronomy. (A shorter focal length provides a wider field of view, measured in degrees.) The focal length also determines the field of view. (This is also referred to as the telescope’s “aperture”.) The focal length of the telescope, divided by the focal length of the eyepiece, determines the amount of magnification. The size of the lens (known as the telescope’s “objective”) determines the amount of light the telescope can collect. The glass lens “refracts” (or bends) the light so that it reaches a focal point. It’s simple, elegant, and easy to understand. The light enters the telescope through this lens, then exits the telescope through the eyepiece for viewing. Its design is really pretty straightforward: A refractor is made of a long optical tube with a convex glass lens at the main opening. The refracting telescope was most likely invented in the mid-1500’s by Leonard Digges (although Galileo Galilei is often credited as the inventor of the telescope). Think about George Washington, at the height of the American Revolution, looking through his spyglass telescope to monitor the movements of British troops – this is a classic example of a refracting telescope. Why? Because it’s by far the most classic-looking type of telescope. ![]() If you ask the average person to describe a telescope, they will probably be thinking of a refractor telescope. What exactly are the key features that differentiate reflectors from refractors? Refractor Telescopes – The “Classic” Telescope Design refracting telescopes … let’s start with the basics. ![]() Refracting Telescopesīefore we dig into the pros and cons of reflecting vs.
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