Impressive Telescopes
Oct 20 '01
The Bottom Line Large apertures and quality optics are what really counts. Fancy electronics will not enhance your viewing experience.
If you are serious about observing, not many of the telescopes listed in epinions are going to be right for you. I've been a serious observer for about 20 years. I'm one of the founding members of an astronomy club with about 70 members. We've been around for about three years. Not long ago, we received $1,000 in grant money for a public telescope. We didn't even consider running out to the mall to purchase a telescope. We did some shopping at a nearby hobby store that low to mid priced telescopes in stock. They carry Meade and Celestron.
There is a major telescope dealer one of our members knows very well that is about a two and a half hour drive from us. They carry several brands and have a significant selection actually in stock. He borrowed two telescopes for our evaluation. One was a 12.5" f4.8 Meade Dobsonian mount reflector. This is a massive 110 lb telescope that costs about $800. The second was by a small company called Discovery Telescopes. Originally, this company was a sub-contract maker of mirrors for other well-known telescopes. A few years ago, they started making dobsonian telescopes themselves. Their largest piece is a 17.5" f/5 185 lb monster that costs about $2,500. They have telescopes as small as their 6" f/8 telescope, a fine telescope for a beginner or intermediate observer that weighs in at a manageable 41 lbs and costs $300. We settled for their 10" f/6 Premium Dobsonian which weighs 85 lbs and costs about $950.
Many observers have dobsonian mount telescopes in our club. I have found this to be similar at other observing events. The bulk of the dobsonian, dob for short, users have 6" or 8" telescopes. One has a 10" f/4.5. No one has larger. Let's briefly talk about these f/ numbers. They refer to the focal length of the telescope. If you multiply your aperture and your f/ number, you get your focal length. For example, a 6" f/8 and an 8" f/6 both have a 48" focal length. Our 10" f/6 obviously has a 60" focal length. If you divide the focal length of the telescope by the focal length of the eyepiece, you get the magnification. I have an 8" f/6 telescope. That's a 48" or roughly 1200mm focal length. If I put a 25mm eyepiece in, the magnification is 44x. If I put in a 10mm eyepiece, the magnification is 120x. The useful maximum magnification for a telescope is twice the aperture expressed in millimeters.
For example, my 8" aperture is 203mm. Anything beyond 400x magnification would have a poor image quality. In reality, a larger telescope anything beyond 400x will have poor image quality, even if you are talking about a 32" observatory class telescope that cost some university $500k. The atmosphere is to blame. This is why many observatories are on mountain tops, less atmosphere to look through. If I observe at home, my elevation is about 350'. Where my club's site is, the elevation is about 2,600'. It is somewhat darker and the air is somewhat cleaner. I live in the outer suburbs. The club is in a rural area. This has part of the reason for better viewing, but the high elevation is equally important. Fortunately, magnification is the least important issue with telescopes.
So why did we chose the 10" f/6? Another thing about short f/ numbers. If it is a reflector, you experience something called coma, even with a good telescope. The outer edges show the stars as ovals, not as points. This problem tends to be minimal once you get to f/6 or f/8. The 12.5" f/4.8 showed nice crisp images. One impressive thing was looking at Saturn and being able to pick out six moons. With my own 8" telescope, it is possible to get five under the best situation. The sixth being Enceladeous, which is very dim, only magnitude 11.7. Next to a brilliant magnitude .67 Saturn and only about four "Saturn widths (not including rings)" away Saturn tends to overpower this tiny moon. Even if I'm just looking for a magnitude 11.7 star not close to any bright object, it's tough with an 8" telescope.
The 10" f/6 was easily as crisp and contrasty, despite being a smaller telescope. This is partly due to the longer focal length, partly due to slightly better optics. We liked the lighter weight and better construction as well.
Now we have a telescope that can impress even the more advanced observer. There is a retired person who has visited us driving an RV. He's not a member, but I've met him at about three of our functions, and probably another three others. He hauls around a 20" f/5 telescope with optics the would rate around an 9 on a scale of 1-10. My own telescope I'd give a 7. Our club's telescope I'd give at least a 7.5 and maybe an 8. Pointing straight up, you need to use a ladder to view through this man's telescope, as the eyepiece is about 8' from the ground once it is assembled. This is a big telescope. I got to spend a few minutes with him and his big telescope. It set him back about $6,500 for just the telescope. He has trouble moving the pieces. The mirror box weighs 120 lbs. wants a "small" travel scope. He chose a 12.5" truss style dob from Discovery. The mirror box weighs 50 lbs and by his standard, $2,000 is not a lot of money (I wish I could say that).
If you visit an astronomy club, you will most likely meet folks with 6-10" telescopes of above average quality. The club may own, or have members or visitors with even larger/better equipment. This will expose you to some really impressive views.
Then after meeting other observers, you will have a much better idea about what you want. Reading stories and talking on the Internet is fine, but no substitute for going out and observing.
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Epinions.com ID:
cottagecrafts
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Location: NY, USA
Reviews written: 2
Trusted by: 0 members
About Me:
Professional woodworker since Spring 2000.
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