A Telescope Tour


For the past few days, I’ve done a lot of talking about differences between types of telescopes and mounting systems. On occasion, I’ve mentioned some of their parts, though I haven’t focused on that.

Today, I will.

This post is meant to be a brief overview of differences between telescopes and their parts. If you want some more in-depth explanations, I’ll link back to those I’ve already written.

In the image above, you see just a few different examples of telescopes. And just in this image, they range far and wide. Most stand on tripods, but some don’t. I can see two different telescope shapes. Some have the eyepiece in different places.

There are more variations of telescopes than are shown here.

So climb on board…I’m about to take you on a telescope tour!

How to Tell a Reflector from a Refractor

It’s easy. A reflector is a straight cylinder; a refractor tapers off a bit.

Here’s a reflector:

reflector tube

And a refractor:

refractor tube

Reflectors: How to Tell a Newtonian from a Schmidt-Cassegrain

Both are reflectors, so they will both always be straight cylinders. But a Newtonian has the eyepiece on the side. A Schmidt-Cassegrain has the eyepiece on the end.

Here’s a Newtonian…

newtonian tube.png

And here’s a Schmidt-Cassegrain.

schmidt-cassegrain tube.png

A Schmidt-Cassegrain can be easily mistaken for a refractor since they both have the eyepiece on the end. But a Schmidt-Cassegrain is a reflector, so it will always be a cylinder, whereas a refractor tapers off a bit.

Mounting: How to Tell an Equatorial from an Alt-Azimuth

Here’s an equatorial mount:

equatorial mount.png

Your equatorial mount can follow objects across the sky easily because it only moves the telescope on one axis of rotation—right ascension. (That’s the orange axis.) Once you’re pointed at an object, the pink axis (declination) doesn’t need to rotate at all.

And here’s an alt-azimuth (or alt-az) mount:

cassegrain copy.png

On an alt-az mount, both axes must rotate to follow an object across the sky. The altitude axis makes the telescope do a motion a little bit like nodding your head, and the azimuth axis makes it rotate on its tripod—like screwing off a lid.

Alt-az mounts are often called fork mounts because they look like they have two “tines.” But they don’t always have two tines…


This mount is also an alt-az, meaning that it has axes of altitude and azimuth. But it’s not a fork mount.

Telescope Parts

Here are just a few basic telescope parts…


And here’s where you can find them on a telescope.

refractor accessories

As you can probably see, finder scopes come in all shapes and sizes…

Finder Scope Variations

I could spend ages on the different types—they’re almost as varied as telescopes themselves. What you’re looking at above is a simple laser finder scope.

laser finder

This little gadget has a screen inside its tube that lights up with a single little dot when turned on. If you look through it, you’ll see that dot land on the point in the sky your telescope is aimed at.

Well, unless your finder scope is misaligned…

But that’s a whole other story. Anyway, my favorite finder is the telerad, which is by far the coolest finder scopes get.


This nifty little gadget perches atop your telescope like any finder scope. It works pretty much the same way as the laser finder, but it lights up with a big red target symbol instead, like you see in the image.

The only disadvantage to a telerad is that you have to look through it at the right angle to see the target.

But it’s worth it. Notice that telerads don’t have a tube to look through. It’s much easier to see where you are in the sky when you look through one, as opposed to a laser finder or one of the more traditional finder scopes. Both of my telescopes use telerads.

Here’s a traditional finder scope, by the way.

finder scope

These traditional guys are every bit as varied as telescopes. Some are smaller or larger. Some have twice as many of those silver screws you see. Some actually magnify, just like the telescope itself. (I’m not a fan of those, but they serve their purpose.)

The purpose of a finder scope is simple, and they exist to make an astronomer’s life easier. In the day and age of advanced computer technology, we don’t need finder scopes quite as much. But they’re still good to have, in case computers fall short.

Telescopes magnify. That’s basically the whole point of them (even if it isn’t the most important of their powers). And because telescopes magnify, it can be hard as heck to search the sky for an object when looking through the eyepiece.

Why not just find the object in the sky and aim, then?

Because…I hate to tell you, but it’s really hard to find an object in the sky and aim. Telescopes just aren’t made that way. It can take upwards of a half hour just to find Jupiter and get it in the eyepiece, even if you know exactly where Jupiter is.

Why? Because, again, telescopes magnify. If you had an eyepiece that didn’t magnify and saw the sky just as your eyes do, maybe it wouldn’t be so hard…

But…wait! We do have an eyepiece like that! Except it’s called a finder scope.

See, that’s the magic of a finder scope.

And it’s good to have even if your telescope is computer-operated—there’s a high chance you didn’t align your telescope’s computer to the sky’s rotation perfectly, and you’re going to need that finder scope to help adjust your telescope’s aim.

There are also oodles and oodles of different types of eyepieces and filters…and while we’re talking about cool accessories, why not talk about camera types…

Actually, this time, I think I’ll refrain.

Here’s the bare bones: Eyepieces magnify, and the smaller ones magnify more than the larger ones. Filters screw on inside the eyepieces and help you see objects that don’t contrast well with the night sky otherwise.

And…that’s really quite enough on telescope accessories for one post, don’t you think?

I decided not to write a post on adaptive optics, since I pretty much covered it with improved telescope mirrors. But tomorrow we’ll do interferometry.

15 thoughts on “A Telescope Tour

  1. Ha ha! I know exactly what you mean with the self centred thing. It’s a fine balance though isn’t it? For me I’m with Victo, I like the personal stories backed up with ‘the science bit’ ‘cos I like to learn stuff. You would connect with more non science-y people if they had a conduit to the science such as personal stories. Part of IFLS success is how relatable it is – not saying your stuff isn’t because I’ve only read one post thus far.
    But everyone’s different why not ask your most loyal visitors what they think via a poll or some such?

    Liked by 1 person

    • Thank you for taking the time to comment! 🙂 I appreciate the input, and I like the idea of a poll. I’ve done that before, but with minimal success. No need, though—I am planning on writing that personal story post, probably sometime in the winter. Thanks for backing that idea—it’s given me more impetus to write it, since I know multiple people will probably like it!


      • Ooh that’s a good one. My dad has one of those and we call it Nomad because its tripod reminds us of something from Star Trek…those guys are good. That’s just the right size that it’s not too hard to set it up single-handed, but it’s still a powerful scope. I have a C11 (Schmidt-Cassegrain 11-inch), and it takes both my dad and me (with difficulty) to get it on the tripod.

        Liked by 1 person

      • Yeah, my dad does the same thing with his. Goes on stints of using it and keeps it set up. But it’s good for him, since it’s not too bad to set up himself. He’s jealous of M Infinity though. That’s what I named my C11.

        Yes, a C11, but I wouldn’t have it if not for a few contributions I made in astronomy outreach to the community. It was a gift from a stranger, there’s no way my family would have been able to afford it at the time. Unfortunately I don’t think I’ll be telling that story on my blog, astronomy-related as it is—not exactly a description of how things work in the field, is it?

        Liked by 1 person

      • Maybe pass it off as a story from the real world…connect astronomy to everyday life. I wonder if that would align with the purpose of the blog, to bring science to people’s doorsteps…by showing that I’m really not that different from anyone else, showing how astronomy and then telescopes became a part of my life?

        Liked by 1 person

      • Hmmm…I suppose interferometry can wait…maybe I won’t keep “accidentally” telling people my whole telescope story if it’s already on the internet for all to see…

        Okay, you’ve convinced me. I sort of may have started up a bit of a related ramble in this comment, and then was like, nope…you can do that in a post instead.

        Liked by 1 person

      • Already started writing it, actually. Heh, a story that doesn’t explain how anything works and is just about how I got my telescopes (albeit connecting astronomy to daily life). I’m not sure if my excitement to go with that is self-centered or not… 🙂

        Liked by 1 person

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