84 replies to this topic

[scooke]

there are plenty of rough optics and bad corrections on mirrors from China.  However, there are vastly more telescopes with bad local seeing due to thermal issues from all areas at all times.  People blame it on other issues and do not realize the problems.  Collimation and thermal correction would make 90% of the people happy with their telescopes in my opinion.

[CHASLX200]

there are plenty of rough optics and bad corrections on mirrors from China.  However, there are vastly more telescopes with bad local seeing due to thermal issues from all areas at all times.  People blame it on other issues and do not realize the problems.  Collimation and thermal correction would make 90% of the people happy with their telescopes in my opinion.

The way the mirror cells are built on some of the cheaper scopes can cause seeing problems since the scope can't cool as well. I have seen scopes were the back end is blocked off that no air flow is allowed.

[infamousnation]

Your location for seeing is questionable. How long have you been observing and how many bands have you seen on Jupiter with your scope for example?

Seeing is not so hot here.  How long, more than 20 years?  I see NEB and SEB always, NPR and SPR dont stand out as well, but are usually visible.  The trop zones look whitish, nothing really shows up in them.

 

On Saturn cassini division is visible most of the time in my 4 inch.  I can usually tell there is some banding on Saturn, but it's not too distinct.

[Daniel Mounsey]

Seeing is not so hot here.  How long, more than 20 years?  I see NEB and SEB always, NPR and SPR dont stand out as well, but are usually visible.  The trop zones look whitish, nothing really shows up in them.

 

On Saturn cassini division is visible most of the time in my 4 inch.  I can usually tell there is some banding on Saturn, but it's not too distinct.

 

My apologies on the delay here. This is reasonable information. Unfortunately you have a few things going against you. You got planets on your southern horizon plus you're plagued with jet streams quite often. So, IMO, I'd settle on something like an 8" or 10" because they're portable enough that if you take it out and the seeing is bad, you have something that's still reasonable in size to haul back in. What I hate most, is setting up a 20" and going through all the necessary steps to get it up to optimal performance, only to realize the seeing just isn't going to cut it. I suppose you could hope you have a decent night once in a while, but I really don't think your platform is ideal enough to bother dealing with anything larger. 

[CHASLX200]

My apologies on the delay here. This is reasonable information. Unfortunately you have a few things going against you. You got planets on your southern horizon plus you're plagued with jet streams quite often. So, IMO, I'd settle on something like an 8" or 10" because they're portable enough that if you take it out and the seeing is bad, you have something that's still reasonable in size to haul back in. What I hate most, is setting up a 20" and going through all the necessary steps to get it up to optimal performance, only to realize the seeing just isn't going to cut it. I suppose you could hope you have a decent night once in a while, but I really don't think your platform is ideal enough to bother dealing with anything larger. 

Maybe you need a small test scope to try out first. That way if the seeing is bad you save lots of time on a big scope.

[barbie]

there are plenty of rough optics and bad corrections on mirrors from China.  However, there are vastly more telescopes with bad local seeing due to thermal issues from all areas at all times.  People blame it on other issues and do not realize the problems.  Collimation and thermal correction would make 90% of the people happy with their telescopes in my opinion.

I don't know what Chinese telescopes you've been viewing through but my Chinese 6" F8 Newtonian has excellent optics!  Very smooth and well figured with mechanicals and a mirror cell that promotes easy collimation and rapid cooling.

[Daniel Mounsey]

Less expensive to go with a lower cost mass produced dob and check the optics. If they need refiguring, that can always be done, but you already have a working telescope with all the components you’ll need. 

[Mike Lockwood]

Less expensive to go with a lower cost mass produced dob and check the optics. If they need refiguring, that can always be done, but you already have a working telescope with all the components you’ll need. 

Refiguring of some low cost optics is not productive or wise due to poor quality of glass and poor quality of anneal.

[infamousnation]

I'm thinking about 8 or 10 inch goto dob from orion or skywatcher. Prices are great and not too heavy. What would the difference in cooldown be? How much difference would adding a fan make?

[Deep13]

Honestly, there's a lot that I don't really like about Chinese Dobs and it's why I went with Discovery in 2000 when there was still a choice in entry-level scopes. In addition to being hit or miss in figuring, the steel tube is a thermal conductor, is easily dented, and does not allow air flow around the mirror--unlike a wider-than-apeture sonotube. And I have a hand-figured Terry-O Pyrex mirror with enhanced coatings, which are in good shape after 17 years.