Monolith149 Daily

Another place to see what KG is doing...

Buying a Telescope - Part 1

Day 22

Back in the planetarium days I was frequently asked about buying a telescope, especially around Christmas. Over the decades since then people still ask me from time to time and still ask more often around Christmas. I had a pretty well-formulated answer eventually and I’ve written it up a number of times. (I’m not sure if I know where any of those old write ups are).

We’ll start with the basics, what’s important when it comes to telescopes: aperture, mounting and portability.

Note that magnification, computers and electronics, and accessories aren’t on the list.


When it comes to telescopes, aperture is more important than anything else. Like a bucket in rain, a telescope’s most important job is capturing light raining down from stars, galaxies, planets, etc. Light carries information and the more light that’s gathered the more you can see. This is why the next big observatory is always about how large the aperture of the next telescope is going to be. In my early years, the 200-inch Hale Telescope on Mount Palomar was the largest. These days we call it the five-meter telescope. Now we have the E-ELT European Extremely Large Telescope in the queue at 39 meters.

The aperture is simply the diameter of the main lens (on the front) or the main mirror (in the back) of the telescope.

In the past, most amateur astronomers might have a six- or massive eight-inch telescope. A 12- or 16-inch was truly gigantic. Now, it’s not uncommon for an amateur to have a 24- or 30-inch telescope. The 10- and 12-inch apertures are not uncommon.

Basically you should get the largest aperture you can afford, that has a sturdy, stable mounting and is portable enough to use. That last part is the trick.


After the aperture, the next important feature is the mounting. A good mounting should be sturdy and solid. If a telescope shakes, even a tiny, barely perceptable amount, it degrades the image.

I know of no better example of this than binoculars. It’s a great joy to take a nice pair of binoculars out and look at the sky. But put them on a camera tripod and it’s like you suddenly switched to HD. More details suddenly become visible. It’s because our hand-holding always shakes at least a tiny amount and it’s enough to make a difference.

A good mounting should also be easy to set up. Some equatorial mountings seem like they take 30 mintues to assemble. Some Dobsonian mounts take about 10 seconds.

The mounting should also make it easy to move the telescope smoothly to point it at the objects you want to observe. It should easily stay where you point it.


I can’t tell you how many times I’ve given all of this information to people, answered their questions, and hear from them that they finally got their new telescope! Then later I find out they’ve only used it one or two times and then not since. Often never.

Many, maybe even most telescopes are bought and only used once or twice and then abandoned. One implication of this is that there’s a huge supply of nearly new, “used” telescopes if one could only find them.

I’ll address another aspect of this try-and-abandon problem later, but a huge factor is portability. The basic rule is, the less a telescope weighs the more it gets used. Smaller is better in this sense, exactly the opposite of aperture. Having the nicest, big telescope doesn’t do anything for your observing hobby if you never want to take it out and set it up. On the other hand, a smaller telescope that lets you grab and go is an instrument you’ll use. That makes it more enjoyable regardless of what it’s aperture is.

For this reason, it’s a good idea to try before you buy.

I truly love my 10-inch Dobsonian telescope. It will always be my favorite. However, sometimes I find that I hesitate to take it with me. I find myself thinking I wouldn’t mind something more like a six-inch Dobsonian, purely for portability, convenience, and my back.


In Part Two I’ll make actual recommendations and in Part Three cover some details about other things I’ve alluded to.


I wrote this and the Part 2a posts while away from home using a Amazon Kindle Fire HD, the Amazon Basics Bluetooth keyboard, Draft software, and saved the files to Dropbox. I currently don’t have a set up for posting when not at home so I just wrote the entries and posted them when I returned.