For me it seems the temp difference is a little more in winter but not much. It often is about 3+C difference so far in the cold months and about 2-3C in summer for me.
As far as mounts go. If anyone thinks a G11 will handle a huge wind sail like that they are dreaming. No way. Anything over 5kmh will wreck the guiding. I am talking from experience with my 12.5 inch RCOS and Tak NJP. Under calm conditions it did OK even though it was really too heavy for the NJP but anything over 5kmh was no good. Sometimes I got away with putting a heavy tall tray on the roof in front of the tube to create a wind break. But that was when the wind was only about 10kmh and even then it did not work well.
It'd be OK if you had high observatory walls and the mount sitting a bit low. But these long tubes stick out past the average observatory wall and into the wind stream by about 300mm depending on your situation.
Funnily enough my TEC180 is not particularly wind affected on the same mount. But then again the tube is only 200mm in diameter versus about 400mm.
So not the best type of scope for a windy area. A truss is quite an advantage in that situation or situate your observatory in such a way that common winds are blocked somehow.
Basically a large scope on a lesser mount will mean unreliable results. Sometimes it will be OK and other times not. Balance and polar alignment would have to be perfect. PEC would be a big plus as well. But wind shielding would be a deal breaker if its missing.
Perhaps a curved piece of metal that you can attach above your roof line (assuming a flat roof) that creates a wind tunnel may be workable.
Say something about 500mm tall and 500mm in a U shaped perhaps a cone style leaning slightly backwards.
I'd be interested to know how much the aluminium tube affects focus with changing temperatures. I suspect it will but perhaps not that badly.
Greg.
Quote:
Originally Posted by Paul Haese
Thanks Greg for the tip. I would hazzard a guess and suggest that this particular issue is more extreme during the the summer months. Would that be correct? Day time temps at my observatory during winter are pretty stable as we are close to the ocean. Night time the temperature usually drops around 5 degrees at most so cooling should happen pretty quickly but I reckon cooling for an hour would be best. I gather you have dew control in place?
Allan, I don't know. This thing is pretty big. It is 860mm long and 370 mm wide. That makes for a pretty large sail in the wind. Even a slight breeze will create havoc for guiding with the G11. Added to that; 22kg combined with finder scope, camera and cables and you are nearly at the 25kg payload of the G11. It might be ok in an observatory and mounted on a G11 but it would be a punt to try it. Mind you as you say there are plenty of examples of large scopes being on top of lesser mounts.
|