View Full Version : Podcast: Choosing and Using a Telescope

2007-Apr-25, 09:45 PM
Buying your first telescope can be a nerve-wracking experience filled with buyer’s remorse. This week we discuss the basics of purchasing your first binoculars and telescope. ...

Read the full blog entry (http://www.universetoday.com/2007/04/25/podcast-choosing-and-using-a-telescope/)

2007-Apr-30, 04:12 PM
Of course, every astronomer will have some other opinion. That's a good thing, in my opinion. That's why the first step should be to look up a local astronomy club. For one thing, you may be able to try many instruments before you buy anything. I did. In fact, my rule is to never buy anything without trying something like it first. I have broken the rule, and it has bitten me on the nose.

I disagree on the 7x20 binoculars, for example. I have 8x21, 8x42 binoculars and 22x60 and 240x254 scopes at my beck and call. The 8x21 binoculars are 3.5 oz (100 grams). They fit in my pocket, so I basically always have them. The 8x42 binoculars get 4 times more light - 1.5 magnitudes. But they also weigh 22 oz (620 grams). It's much harder to hold them for any length of time. And i'm really only looking at brighter objects like the Moon and planets. At 10x or higher magnification, you need a tripod - and the portability goes down again. In fact, the 22x60 is on a tripod, and I almost never use it anymore (except for bird watching). So, for me, it's naked eye (1x7), small, durable $50 8x21 binoculars, and a ten inch Newtonian on a Dob mount. YMMV.

But the process is the 3 P's. Price. Performance. Portability.

My case (last year) went this way. Price: $1000 for everything. Scope, accessories.
Performance: I want as much aperture as I can get. Astrophotography not essential.
Portability: It has to fit in the car. Anything that won't is a non-starter.

$1000 prevented getting an 8 inch SCT (compact reflecting scope), at least new. To bad, because it might allow astrophotography later. The largest Newtonian Dob in that range was 12 inches, maybe 13. However, the 12 inch Dobs I'd seen would not fit in my car. Orion makes a 10 inch Dob with a 48 inch focal length. It fits across the back seat. It's cheap enough that I could consider getting a computer locator for it, which I did. About $900 delivered. $100 extra can be used for a moon filter (get the variable polarizing kind), and a nebula filter (Oxygen 3), and maybe a planisphere (I use Planetarium on my Palm Pilot).

The computer locator has been awesome. As a rank novice, i can see maybe two objects an hour without one. With one, i can see about 12 objects an hour. And, most of that time is spent looking at them. So, observing is more enjoyable, and i end up doing more of it. I'm also getting better very quickly. After all - i do have to find alignment stars, which requires at least a minimum of navigation.

Other people have made other choices with nearly the same constraints.

Some claim that your astrophography setup should be a tiny refractor. One guy uses an 80 mm refractor. Why? You can get more light grasp by taking longer exposures. A small scope requires only a small (and much, much cheaper) mount. Short focal length scopes have wider fields of view. So it may be cheaper and better to have two scopes. One optimized for photography, and the other optimized for visual astronomy. YMMV.

Here's an interesting comparison.
Saturn with naked eyes: It's a bright dot.
Saturn with 8x21 binoculars: It's a line. Weird!
Saturn with a 22x60 spotting scope. The rings are clearly rings. Titan is clearly a moon.
Saturn with a ten inch telescope. The rings have structure, like the Cassini division. The planet has bands on it, and the shadow of the rings is visible. Several of the moons are evident.
Saturn from the Cassini orbiter - just awesome. A totally new discovery every month. And Huygens resolved features on Titan that were about an inch across!

About that 20 inch RC dream? Totally non-portable. My club has an observatory which i can use at will. And, some of those club members help maintain it. 12.5" Cassegrain. 22" Dob. 10" SCT. Cameras, etc. These things are much more fun to use with the group.

2007-Jun-07, 02:17 AM
I want to look through the Keck scopes