Tuesday, September 2, 2008

Cut to the Chase: Larger Scopes

So a scope of 5 inches aperture or less isn't going to do it for you?

Never fear! There are a lot of good larger scopes to be had.

Now, I'm not going to recommend going out and buying that 18 inch monster as your first scope, even if you can afford it and possibly could even make use of it. Even if you end up getting one as your second scope, it better to start smaller and work your way up. After all, think of how you'd feel if you went ahead and got it, then six months later decide your true love in telescopes is a high performance large aperture refractor?

Get a good all-around scope before you start getting specialty scopes. If astronomy is really the hobby for you, your first scope won't be your last. If you end up just being a casual astronomer, having a good all-around scope that is convenient to take out a few times a year is far more valuable than having a complex monster you've never got the time and energy to get under starlight.

So I recommend a six-inch or eight-inch reflector for a first scope. In general, I recommend these more highly than the portable scopes I described earlier, but which one is for you depends on your tastes and what circumstances you expect to be observing under.

For a mount, I recommend a Dobsonian mount more highly than an equatorial mount. The Dobson mount is easier to use and set up, lighter, easier to pack in a car or carry in and out of the house or garage. With a Dobsonian there are basically only three things to move: the base, the telescope tube, and your accessories box. Setup usually only involves setting the tube in the base. Then all you have to do is take the cover off the end of your tube and the plug out of the eyepiece hole, put in an eyepiece, check your finder's alignment, and off you go.

You'll also want to learn to collimate the scope, but on a well made scope you shouldn't need to do this often. To learn this, find another amateur who teaches this, or get someone at the store you bought it from to teach you. If nobody at the store knows how well enough to teach it in a simple fashion, find another store. It's the sort of thing that is easy to teach in person, but sounds horribly awkward and complicated in print. So don't be scared, it's really not that hard. My daughter learned to collimate her own scope when she was 10. I think half the problem is the word "collimate." It sounds so technical and complex. It just means lining things up inside, and you can tell if they're lined up by looking at them, just as you can tell which way a car is turning by looking at the front wheels.

Now, which telescope to buy?

I don't have any specific recommendations, though the scopes from Orion and Meade of this type are nice and attractively priced, in my experience. There are lots of folks who own these scopes, go to the forums where they hang out and ask them their experiences (as well as for other brands you may consider.) They can usually tell you what additional accessories you should expect to buy right off (for example if you'll need a better finder, or a supplementary eyepiece to the one included) as well as any tweaks you should expect to make to the scope "out of the box."

Since the manufacturers update their designs frequently, any such statements I could make here would probably be out of date by the time you see them.

One point I should make is not to underestimate the six inch scope. A well made six inch scope with good optics will outperform a so-so eight inch scope. I know this for a fact. My daughter's six inch is a far better scope than an older eight inch commercial scope I own. Her little six inch f/9 telescope gives clearer views, better contrast, and more detail than my big fancy-looking eight inch telescope--at least as it came from the factory. Once I saw how much better my daughter's scope was, I made some modifications that have improved it to where it's about on a par on bright objects and slightly better on objects that are dim enough to be marginal in her scope. I plan on doing a major overhaul on the scope someday. It effectively won't even be the same telescope when I'm done with it. Among other changes I'll be re-grinding the mirror and putting it in a new tube. That's how major I'm talking.

In a six inch I can highly recommend an f/8 or f/9 scope. For an eight inch an f/6 or f/7 scope will be good. You can get a "faster" scope (scopes with a lower f/ratio number are called faster because the light comes to a focus in a shorter distance, thus "faster" than a scope with a higher number. An f/6 scope is "faster" than an f/8 scope.)

Check with current owners before buying, and get a chance to play around with one, too. It should move smoothly along a diagonal line. It should stay put when you stop pushing it. You should be able to point it at something far away, tap the tube sharply, and it should still be pointed at the far away object (when looking through the eyepiece at a magnified view, of course.) It should have the eyepiece at a height that you can see through it both when it's pointed straight up and when it's level with the ground without breaking your back or neck. Uncomfortable stances aren't going to help you see the sky, they're going to leave you inside with an icepack and keep you from taking the telescope out again because using it hurts!

Observing should be reasonably comfortable. You can use a step stool or an observing chair, but you shouldn't have to for this first scope. It should be usable from at least an angle pointing up only about 20 degrees (about the slope of a low roof) to straight up without you needing any help. If the telescope's tube can rotate easily in the cradle without a lot of fuss and without throwing it way off balance then this is a big plus for comfort. Some scopes come with two sets of "ears" or altitude bearings so that you can rotate the tube 90 degrees for different eyepiece angles. My preference is having the eyepiece set at an angle of about 45 degrees from the ground or even a little higher when the tube is in a flat position. This lets you see into it at low angles without destroying your neck vertebrae, and when it's pointing straight up the eyepiece is going to be horizontal no matter what angle it's at when lower.

Check stability with the scope in different positions. Make sure you can adjust the balance of the scope tube. If the tube doesn't slide in its cradle, you may need to add some sort of counterweights--see what current owners say. There are some cheap and simple ways of doing this. One of my favorites is weighted bags that grab onto Velcro strips placed on the telescope tube.

In my case, I have the luxury of building my own scopes, so I always make the tubes so they can slide back and forth with respect to the ears and rotate around their axis to bring the eyepiece to a convenient angle. Most commercial scopes don't do this, though, because it would cost more and most people look at price, not at usability features like this. If the market demands it, they will build it, but if it doesn't, they'll build for lowest price. Unfortunately all too often the market doesn't know what it's missing when it goes for lowest price.

And, as mentioned before, go to a star party and see what others are already using and talk to them about them. There's the added advantage that if you get the same scope as someone else in your area, you'll always have someone else to keep you up on good ideas for your scope, accessories, and give you an idea of what you can get out of your scope. And you can do the same for them.
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