sharp at higher power

I have an Orion 10" (XT10) dob, that I like very much, except that at above 200 power, everything gets fuzzy. I am using a Televue 6mm Radian, giving 199 power, and all the stars are discs, and Jupiter just has two blurry bands, no detail at all. E and F in Orian's trapezium are not there even under the best skies. Am I expecting too much from this scope? Is it a case of you get what you pay for? Zambuto mirrors in scopes of this size run $4000 and up. Do I have to go to this price for sharp optics at higher powers?

Thomas,
How do the images look at low power? Are they clean and sharp or still a little fuzzy? When you focus with the 6mm, is the focuser racked in/out all the way with no further room to go? If so, you might have to move the main mirror forward or backward in the tube...not a fun thing to do! Also, have you checked the collimation of your mirrors. That might be the biggest issue and I would look into that before I started moving the mirror around. I had an Orion 8" reflector that had good optics, so I doubt if you have a bad optical system. I hope this helps some.
Pete

Thomas,

There are two of these scopes in our local club. Both perform very well.

Currently, the jet stream is directly over Tenessee. Under these conditions, you will have seeing difficulties and will not be able to use high power. Jupiter will appear as you have described it.

You will get better seeing when the jet stream moves out.

clear and steady skies,
dan

Hey...Pete and Dan have it right. There is probably nothing wrong with the scope. A cool link to see what the jet stream is doing:

http://www.wunderground.com/US/Region/US/2xJetStream.html

The #&*@! jet stream overhead wrecks the seeing. So does looking over houses during cold weather. Jupiter is pretty low in the sky, also, which doesn't help.

Steve

My 8" Orion gives me great views and shows me all the things you're not seeing. I think these scopes are well enough made that you should expect more. Rule out things like miscollimation, thermal currents in the tube, jet stream, seeing, etc. If still no go, talk to Orion, they're very easy to deal with in my experience.

I had the same trouble trying to get a good high- powered look at Mars with my Orion 8" (XT8) Dob. But, now I'm thinking that the combination of Mars moving away (in mid to late January), the jetstream, and a nearby apartment building might have been the culprit.

thomas Burleson said:

I have an Orion 10" (XT10) dob, that I like very much, except that at above 200 power, everything gets fuzzy. I am using a Televue 6mm Radian, giving 199 power, and all the stars are discs, and Jupiter just has two blurry bands, no detail at all. E and F in Orian's trapezium are not there even under the best skies. Am I expecting too much from this scope? Is it a case of you get what you pay for? Zambuto mirrors in scopes of this size run $4000 and up. Do I have to go to this price for sharp optics at higher powers?

You are not expecting too much of the scope, you are expecting too much of the skies, the "seeing", the stability of the atmosphere.

- Jupiter: Right now Jupiter is low on the horizon in the early morning, even with a reasonably stable atmosphere, I would not expect good views. One wants it at least 45 degrees above the horizon for best viewing but that is not going to happen for us in the US for a few years. Seeing those two bands, that is all you will see in any scope unless the air is stable enough to allow better views.

- The E and F stars in the trapezium. These are also a test of the "seeing" more than the optics. A 10 inch is plenty to see the 6 stars but if the atmosphere is not stable then no telescope can see them..

Your scope is a 10 inch, that means you are looking through a 10 inch diameter column of air that is probably about 100miles in length at Jupiter or the Trapezium. If that air is unsteady, if it turbulent, then it is like looking through a mirage, things are somewhat blurry. Twinkling stars are the result of an unsteady atmosphere, if you see stars twinkling, it's good sign the seeing is not steady.

Another way to determine the seeing is to look at the Trapezium with a scope that is cooled and collimated and see how many stars you see...

jon

Hey Tom, Your 10 inch should be showing you the items you are describing and you don't need a premium mirror to do it, any diffraction limited 10 inch should show E and F easily. It is still possible that it is not a mirror problem but it is pointing more in that direction. If there is a club close by (maybe Nashville) you might be able to get a ROnchi eyepiece or have one of the members test you mirror. You could maybe have a pinched secondary or a primary mounting problem.

Good luck Dave

If it turns out NOT to be the jet stream or collimation and before you move the mirror you might want to try an extension tube in the focuser before putting the eyepiece in. If the eyepiece is not focusing when fully racked out this may help and is a lot less hassle than moving the mirror. I had to do that with several eyepieces in my fast Dob (Meade 10" Starfinder).

My appologies if this has already been suggested.

Dave