After talking about checking out Saturn, etc., several folks have asked about telescopes. This will no doubt start a several post discussion on the subject, but let’s start talking about selection.
First, you have to ask yourself a question. Am I going to be doing this night after night, or just every once in a while. If your answer is night after night, buy yourself a top of the line “big” scope. If not, buy something smaller.
That said, I’m assuming you’re in the occasional department. If you’re in the night after night group, you certainly don’t need this guide.
That means maybe once a week or month, you pull it out, and peer at the Moon or one of the planets. On occasion, you might get a little more ambitious and try to run down a comet or nebula.
First, there are several kinds of telescopes to choose from. They tend to fall into two groups, refractor, or reflector telescope. The difference is this. A refractor uses lenses to gather light. A reflector has a curved mirror to gather light. Both are measured in inches or millimeters across. We call this the “light gathering surface.”
OK, a word about shopping. First, don’t be influenced by photographs in the advertisement UNLESS it says they’re actually been taken through this telescope. I’ve seen more than a few unscrupulous types who have used photographs from the big observatories or even the Hubble in their advertising. While they might not make a claim to you’ll be able to “see” this, the implication is, even if unintentional, that you will. So, you get your telescope, point it at the Orion Nebula and you become disenchanted because you don’t see it like it looks in the picture. Almost never will what you see through the eyepiece look like what you see in the sky. The human eye is at once better and worse than a camera. Cameras can take hours to soak up light. Your eyes won’t.
Another thing to be careful of claims on performance. It’s not uncommon to go to say WalMart and buy a telescope. On the box, they’ll list the magnifications. There’s no way you’re going to get that kind of performance out of small telescope. Let’s say, the box lists the “objective lens or mirror” as 60mm. Sound like a lot, but running that through my handy dandy metric to English converter and that 60 mm comes out about 2.36 inches. Not bad for an occasional use or beginner telescope.
Now, here’s where people get in trouble. They fully expect to be able to get that kind of performance out of a small telescope. According to Sir Patrick Moore in his book, The Amateur Astronomer, what you should expect is about 60x per inch. So out of that telescope, I’d get a max of 150x. Experimentation has borne out his statement. Anything over that 60x per inch then you start trying to magnify something that just isn’t there. The images will become dim and hard to focus on.
What the seller of the scope has done is to give you eyepieces, etc., that will get you up to 150x, and then they’ve tossed in something called a Barlow lens or eyepiece. This increases the magnification of the image by from 2 to 3 times. Problem is, while this works well with big scopes, for a small scopes, it doesn’t. I’ve never bothered to use a Barlow.
Expecting that kind of performance would be like expecting Formula One race car performance from a Go-Kart. as Granny used to say, “It ain’t gonna happen.”
Another thing to look for an occasional use telescope is how portable is it. I own a 6 inch reflector with an equatorial mount. Sounds fancy and it is. Here’s the problem. You have to be in good shape to move it around. Something that size almost demands a permanent setup. Anything bigger and I’d have to have an outdoor observatory for it.
The other is, it’s a little antiquated for the modern amateur. Why? If I want to hunt down an object, I first need to make sure my setting circles are correct, as will be my polar alignment (it will track with the stars). If you bought the cheap telescope at Walmart, chance are you’ll have what we call an Alt-Azimuth which is simple, and stable, but makes tracking object down even more difficult.
Today, there’s technology to the rescue. The wonderful world of computers has come to small telescopes. Many telescopes today can be run from your phone or PC, and can find remote objects with just a few keystrokes. The good news is the technology won’t break you.
A good site to check out is www.telescope.com. This is Orion Telescopes webfront, and they sell their products through the site. Especially, check out the “How to choose a Telescope” link. it echoes some of the things I’ve pointed out here, and gives a great explanation about differences in scopes, features, and so on.
So even the small telescope can be a lot of fun and provide years of enjoyment. It got me hooked, and there’s times I still pull out the small scope and just scout around the stars with it.