Four Infamous Telescope Myths

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tfwthom

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Four Infamous Telescope Myths<br /><br />Stop me if you've heard this one before! Here are some plausible-sounding ideas that turn out to be less than true.<br /><br />By Gary Seronik<br />Gary Seronik is an associate editor of Sky & Telescope magazine and an accomplished telescope builder<br /><br />Amateur astronomers are a gregarious lot. Whether at club meetings or in Internet newsgroups, they share ideas, observations, and experiences, usually with generosity and good humor. Many a newcomer to our hobby has benefitted from this casual exchange of ideas. The flip side of the coin is that the same forums provide fertile breeding grounds for myths that are perpetuated and redistributed, often without challenge. Here is my selection of notoriously long-lived telescope myths. Each contains a grain of truth. Yet they are demonstrably incorrect and may have caused many a telescope owner unnecessary effort, expense, or angst. <br /> <br />"Pyrex telescope mirrors are better than those made from plate glass." <br /><br />The primary mirror at the heart of a reflecting telescope is typically made from either Pyrex or ordinary plate glass. Both materials can be fashioned into excellent mirrors. So why is it so commonly held that Pyrex mirrors are inherently superior? There are two main reasons. <br /><br />First, because plate glass is less expensive, it is presumed inferior — you get what you pay for, right? However, in truth the cost of the substrate material has little to do with the price of the finished mirror. Most of the expense lies in turning that piece of glass into a working optical component. <br /><br />Second and more to the point, unlike plate glass, Pyrex is a low-expansion material. This means that a mirror made from Pyrex is less prone to warping when it is at a different temperature than the air surrounding it. The ultraprecise curve on the surface of a Pyrex mirror isn't as severely deformed when the telescope is moved from a warm house into the cool night air. <div class="Discussion_UserSignature"> <font size="1" color="#3366ff">www.siriuslookers.org</font> </div>
 
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