Buying your first scope

Note: This is a handout for a talk/demonstration given at the Westport Library November 17, 2005. As such,it is intended as supplementary notes - not a complete article.

Six links to a good observing experience

Most telescopes do an adequate job with several of these “links.” But one weak link can ruin the whole observing experience and leave the user frustrated, and ready to quit trying.

1. Finder – Helps you point the telescope at your target. “Red dot” types are good for bright stars, major planets, and the moon. Optical ones help with finding both bright objects and ones too faint to see with the naked eye.

2. Objective lens or mirror – This is the heart of your telescope. It should be at least 60mm in diameter (about 2.25 inches), but larger is better because larger ones gather more light, and what you are trying to see is frequently very dim.
3. Eyepieces should be 1.25-inch (a standard) in diameter. Two are fine to start with and good sizes are typically about 10mm and 25mm. Don’t be fooled by promises of high power. We rarely use more than 200X, and anything much above 100X is frequently useless on a small scope.

4. Focuser –You want a smooth, jiggle-free motion. Even though you are looking at objects that are at infinity, you will find you frequently make very small changes in the focus, and a smooth focusing action helps.

5. Mount – You’ll see three basic mount designs – Dobsonian, alt-azimuth, and equatorial. The Dobsonian is simplest, the alt-azimuth next in simplicity, and the equatorial adds functionality, but also complexity. In any mount what you are looking for is ease of use, portability, and above all, steadiness. When you point the telescope at something and look in the eyepiece, you want the image to be steady – not vibrating as the scope slowly settles down from having been moved. Your best guideline here is common sense – flimsy looks flimsy – though, of course, if you are able to test the mounting for yourself that is even better.

6. Tripod – Once again, the key is sturdiness. Test the tripod by extending it to its highest point. Make sure the joints in the tripod legs lock securely. All tripods will hold a scope – not all will hold them steady, especially if there is any wind. (Dobsonians almost never use tripods.They simply sit on the ground.)

Computer controlled "go to" scopes – These can be very useful. I own two. But I don’t recommend them for newcomers. First, it’s hard to make a really good one that is also inexpensive. Second, the advertising makes them sound easier to use than they are. Third, in my humble opinion they are a poor way to learn and appreciate the night sky. As your second or third scope, a good one can be quite useful. But starting out with one is like being handed a calculator when you have no idea how to add, subtract, multiply, or divide. Besides, it takes the satisfaction out of discovery.