Monday, September 24, 2012

Advice for First Time Telescope Buyers...Contd (4)

Number 4: Telescope Quality

As far as beginner telescopes are concerned, there are many telescopes on the market that are best avoided. Fortunately there are more great choices today than ever before (and at very reasonable prices). Ideally you will spend $500 to get started with an excellent package, however I know that this is out of reach for many. Fortunately there are some nice choices in the $100 range (stick with the ones I recommend however, do not buy any old $100 scope you find)! Many beginner telescopes make performance claims that are preposterous, and are of very poor mechanical and optical quality. You are better off buying a simple (but well made) telescope. In other words, buy a telescope where the money has gone into basic functionality (good optics and a good mount). Telescopes to be avoided are easily identified, since they come standard with numerous (but often useless) accessories (more on this below)!

Of paramount importance in any telescope is optical quality. While a beginner telescope cannot offer custom hand made and certified state of the art optics, ones from reputable manufacturers are generally very good. I strongly recommend avoiding so called "department store" (Wal Mart, Toys R Us, etc) telescopes. Some scopes available from such vendors have a satisfactory main optic, but most of the time the eyepieces (discussed below) are of marginal quality. The very worst telescopes have plastic lenses... needless to say, these units will have extremely poor performance.

The second most important part of a telescope is its mount. There are numerous types of mounts (beyond the scope of this article). They key is to make sure the one that comes with the scope you're considering is smooth, stable, and solid. Few things are more frustrating to the beginning astronomer than fighting with a shaky telescope mount that won't stay put on an object! Poor mountings will make using high magnification especially annoying and frustrating. Purchase a telescope with a simple (but quality) mount.

Another of the important items that come with a telescope are the eyepieces. The eyepiece is where you "look" through the telescope. Eyepieces come in a variety of types and sizes; using different ones allows you to change the magnification of the telescope. Many low end telescopes provide 2 or 3 poor quality eyepieces (many of which result in a magnification well beyond the useful capability of the scope). For small beginner telescopes, it is much better to have one or two quality eyepieces (as opposed to a battery of marginal eyepieces). What is best for a beginner? Look for one eyepiece that produces low magnification (about 30x - 50x) and a second one for higher magnification (about 100x to 120x). Eyepieces are marked with letters and numbers; these characters denote focal length (and often the optical design) of the eyepiece. Beware of telescopes that have eyepieces with any or all of the following markings: H25, H20, H12.5, and SR4. If the scope has one or more of these eyepieces, it is likely that the images will be marginal to poor. The "H" stands for "Huygens", one of the poorest performing optical designs available (they are inexpensive to manufacture however). "SR" stands for Symmetric Ramsden. Trust me on this: no small telescope will benefit from an SR4 eyepiece. The manufacturer simply includes this so that the high end magnification of the telescope sounds very impressive (it is a marketing ploy). Most people will find using an SR4mm eyepiece extremely frustrating. The SR4mm eyepiece has what is known as very poor eye relief. If you wear glasses, the SR4mm eyepiece will be impossible to look through. Eyepieces with poor eye relief require that your eye be very close to them, often uncomfortably close even for those who do not wear eyeglasses. The bottom line: Any telescope will have sharper and brighter images when LOW magnification is used. And, finding objects will be MUCH easier!

Credit and Source:
Joe Roberts

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