What kind of Telescope to Buy? So Many Options…

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We’re gonna take a break this time, in part to allow the celestial “show” up there to change a bit. First,things that you were just gazing at last night will be setting about twenty minutes earlier in two weeks, as new things are rising the same amount of time earlier. Second, we need to explore the vast array of telescopes ready for your careful perusal (you’ve learned at least the “mainstay” constellations by now, right?). Never has there been such a plethora of instruments for the amateur astronomer, nor has the cost been so affordable (for most gear, anyway).

Telescopes basically come in two types: refractors, which use a lens at the top as the light-gathering element, and reflectors, which employ a mirror at the bottom. Which one is right for you?

Think of the occasional movie scene in which a telescope was clearly visible in the background, and it most likely was a refractor. They tend to be beginner scopes, because they are typically small, easy to use, and inexpensive (large refractors are another story-very expensive, and cumbersome; virtually impossible to transport). Not that this author is in any way biased, but two of my three instruments are refractors. A lens seldom needs adjustment. Just a light cleaning once in a while. It’s unobstructed aperture, and yields greater contrast than a reflector’s mirror. They are decent scopes for planets, the moon, and a few clusters and small nebulae. Drawbacks? They do not gather as much light as a garden-variety mirror, hence not as much detail or brightness. A refractor telescope typically sports a lens around three or four inches in diameter, versus a reflector mirror of six to eight inches or greater.

So why buy a reflector? Because you simply cannot get as much aperture for the money. An eight-inch mirror costs $250-$300…a refractor lens of that diameter, depending on whether a classic two-element (called an achromat) or three/four element (apochromat) ranges from $2400 to…well, pardon the pun, but an astronomical amount. No, that last isn’t a typo that slipped past me. Lens grinding involves at least four surfaces to be shaped to a critical tolerance, versus one surface for a mirror. Drawbacks of a reflector? Periodic mirror alignment, for one thing. It’s called collimation, and is critical to maximizing your reflector’s performance. While not difficult to learn, it can be frustrating for a novice stargazer. Contrast an ink-black sky behind the stellar image a refractor yields with the dark-grey background a reflector shows-although not a stark difference, it’s a compelling one. Stars seen through a quality refractor telescope resemble diamonds against black velvet.

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The above scope, in silhouette against the pre-dawn sky, is my Celestron 150mm refractor telescope. This not only represents what an average person can afford in a lens-type scope, but also about as large a refractor as you can realistically haul around. It’s cumbersome, but has just enough aperture for some serious stargazing. It’s a “workhorse” of versatility: this telescope shows stunning planetary images, yet is a pretty decent instrument for Deep Sky Objects (y’know, all those galaxies, clusters, and nebulae). The picture below shows off my current “arsenal”:

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The smaller refractor is what’s known as a “richfield” telescope: think of it as a sawed-off shotgun! Because the tube is shorter, relative to its 120mm aperture, it has a wider “scatter range” (field of view!). Objects aren’t quite as detailed or bright, but the field of neighboring stars around them is greater. With the bigger refractor, I can see one or two words of the phrase…with the smaller one, I can see pretty much all of it. I use the smaller “shotgun” when scanning those star-rich dust lanes in Sagittarius! For Jupiter or Saturn, the big refractor excels.

Lurking in the background of the above photo is my lonely reflector. It has a ten-inch mirror, at the bottom of a hollow tube. The incoming light is bounced off the parabolic curve of the primary mirror, bounced again off the flat secondary mirror, and then sent out to the eyepiece mounted on the side of the instrument. This particular type of reflector scope is called a Newtonian, named after its inventor, Sir Issac.

So again, which one would be right for you? I’ve just whetted the appetite, right? There’s a wealth of information online, far beyond the scope (pardon another pun) of this diatribe. Check them out…and enjoy the learning curve.

Remember, there are two prices of admission to this hobby: learning the constellations (and that’s virtually free of charge), and obtaining an instrument with which to observe (possibly those binoculars I alluded to in an earlier post, although if this “bug” bites hard, you’ll be wanting to graduate to a telescope soon enough!).

Eye Candy for Astronomers (2)

The above is my idea of astronomy “eye candy”…

Happy Star Trails!

Jesse

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