Originally posted by: Jeff7
1.) Around $400 budget, total hopefully.
2.) Not really sure. Seeing what's out there. 🙂 Planets for sure though.
3.) Backyard is good, except for things near the horizon. Then I might have to go to the fields behind the house. Max of like 1/2 mile maybe. There is a city, Allentown, about...15-20 miles away, but there's generally not a whole lot of light pollution from it over most of the sky - just a bit in the direction of the city. I'd say that less than 30 miles away from home (other direction) is an optimal place for viewing.
4.) Storage? I've got a closet, shed, and garage at my disposal.
1) Within the $400 range, you have fairly few options. Your choices include 6" and 8" Dobsonians (
1,
2), small 60-80mm computer-controlled scopes (
1,
2,
3), and 80-100mm refractors on equatorial mounts (
1,
2).
Of those options, by far the best value and the best general purpose scopes are the Dobsonians. Its aperture and focal length are perfect for viewing all kinds of objects. No they don't track as easily as other types of scope, but they make up for this with their versatility. With regards to the computer controlled scopes, the only real negative is the fact that the aperture is very limited. Finally, the equatorially mounted refractors in that price range also offer limited aperture (though larger than that of the computer controlled scopes). The bigger problem is that low cost refractors tend to be undermounted, that is, the mounts are not quite sturdy enough for the instruments that are placed on them. The result is a jiggly mount, which makes the image quiver in a light breeze and whenever you try to focus.
2) This presents somewhat of a dilemma. On the one hand, tracking planets is a lot easier with equatorial mounts. On the other hand, the small refractors that are available to you don't take high magnification very well (remember the magnification rule of thumb...max useful mag = aperture in inches x 50, or aperture in millimetres x 2). With the planets, you need high magnification to get good views, simply because they are so tiny. Even Mars at its closest this past August was 70 times smaller in apparent diameter than the moon, and the moon is only half a degree wide (your pinkie finger at arm's length is about one degree wide). Now, it is about 95 times smaller than the moon. Saturn and Jupiter are much better than Mars simply because they are larger, but even then you need at least 125x to get a good view. That's a tough assignment for an 80mm refractor on a jiggly mount.
The Dobsonians will be a better choice in this price range. Yes you will have to track manually in both axes (whereas you only have to track along one axis with an equatorial mount), but the higher useable magnification is a huge benefit. Furthermore, the resolution of a scope increases linearly with aperture, so an 8" (200mm) Dobsonian will be able to resolve details half as large as a 100mm refractor (this is somewhat of a simplification, but it illustrates the point). For objects as tiny as the planets, resolution is critical to sharp views. There's no sense zooming up close if the planet is a featureless blob.
3) The Dobsonians are the least portable of the bunch, but that's not to say that it's bad. If you have a car with a back seat and a trunk, you're set. The long tube goes in the back seat, and the "rocker box" (the Dobsonian in a Dobsonian scope) goes into the trunk. Nevertheless, the other scopes still win on portability. There's no getting around that.
If you can view most of the sky from your backyard or driveway, that's usually good enough. For comparison purposes, my observing location on my driveway sucks...light pollution is horrible in Toronto, trees block a big portion of the eastern sky, my house blocks the lower part of the southern sky, and the western sky is obscured with the double-whammy of a huge tree
and a streetlight right behind it. Still, my line of sight is good to about 45 degrees from overhead (i.e. half-way between the horizon and overhead in each direction). That's important because you won't often look at things near the horizon, simply because you'll be looking through a thicker layer of Earth's atmosphere (which distorts images to a degree). Looking overhead, you're observing through the thinnest layer of air, which provides the clearest view. So assuming that the view from your backyard is only half as bad as mine, it's still more than enough.
4) Perfect...that's about as good as it gets. It'll be better to put it in the garage rather than the shed because the garage is bigger and thus is less prone to temperature changes. Temperature changes are bad (particularly if your area is generally humid), because as the air warms up in the morning, water will condense onto colder objects that are below the dew point. Dew is a major problem for telescope optics, leaving nasty deposits and attacking the delicate coatings. Of the various types of scopes, reflectors (of which Dobsonians are a subset) are the least prone to dew because the primary mirror sits way back inside the tube and has a long shaft of air in front of it to resist temperature change. On the other hand, refractors have their lenses at the front of the tube, directly exposed to outside air.
I'm probably exaggerating a bit here on the dangers of dew. If your car's windows don't dew up while it is in your garage overnight, then your scope is perfectly safe in there. My garage is like that, and I suspect most others are too. Garages that are part of the house are better in this regard, because heat from inside the house will leak over into the garage and keep it a bit warmer than outside air, preventing dew. In any case, telescopes should always be covered when not in use, and that goes a long way in preventing dew.
