Friday, February 12, 2021

Junk Scopes: Celestron Astromaster AZ

As I mentioned in an earlier article, the market has seen the return of junk telescopes in a big way. Even the big names were not immune to the lure of selling junk to unwitting beginners, and the Celestron Astromaster AZ telescopes is a huge example of that.

These scopes are sold as astronomical telescopes, I mean, "Astromaster" and the AZ referring to Alt-Azimuth mount type for astronomy make that obvious. These are not being sold as "Sporting Optics" (though there is plenty of junk being sold as sporting optics, the bar to being useful is lower there.) These are being sold for astronomy, and they're sure to frustrate anyone who tries to use them that way.

The mounts are basically cheap camera tripods and pan-tilt heads. They are OK for pointing a snapshot camera, or a pair of binoculars. But they are completely inadequate for pointing a telescope at something in the sky. Let's look at some numbers. Binoculars and cameras have a field of view that runs from around 20 degrees of angle to over 60 degrees for a typical consumer item. Cameras have the narrower field of view, binoculars are going to be 40 degrees on up. It's not hard to get something pointed to within that range.

Telescopes have a field of view of about one degree, maybe a degree and half, at their widest (for a typical scope), and often even narrower! That means that to get your scope pointed at something, you have to grab that twisty handle on the tripod head, loosen it, move it to within 1/20th of an inch just to get something big like the Moon in the field of view! And then tighten it down without losing it! That's just over 1mm of accuracy! With your arm, while twisting a locking handle.

That's nonsense, of course!

Not only that, but the sky moves. By the time you get your scope lined up on something, it's already starting to walk out of the field of view. It takes the Moon two minutes to cross the distance of its own width. That sounds like plenty of time to get a look, but it goes fast. Most cheap telescopes don't give a good view at the edges of the field, so you want to look at things centered. And you want to look long enough to let your eye relax and soak up the details. All while messing around with a lousy mount that's about impossible to find something in.

You want to have the ability to use a slow motion control, or have a mount like a Dobson mount that allows for easy adjustments to the scope as you view. These mounts don't do that. They also don't have an ability to balance the scope, so you not only have to fight that handle to within 1/20th of an inch, you have to deal with the fact that your scope is either nose-heavy or tail-heavy and it wants to slide off the subject.

Don't get these things, for yourself or for anyone else.
If you already have one, you should consider getting something else. You are punishing yourself unnecessarily if you're trying to use it for astronomy. If you have the short tube model, it's OK for a spotting scope. The long focal length models are less useful in that role, however.
You can get wider field eyepieces. They'll make it easier to align on objects in the sky. And you can use them with a new telescope as well, so if you give up on your Astromaster AZ, the money isn't wasted.
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