Quote:
Originally Posted by Robh
It is rare that a close double (<1.5") can be easily split (or split at all) simply because the seeing conditions are not good enough. Bumping up magnification will just make the view worse. In fact, it is rare that magnification over x250 will give anything more than a jittery blob.
|
This may be the case with large aperture telescopes, but in smaller ones (like the 6-inch I'm using) 1 arcsec doubles like Xi Sco are perfectly and frequently doable, even from my backyard. The thing with seeing is that is changes quickly and all the time. Even with mediocre (on average) seeing you could still get to see a clear split for, say, 1 out of 10 seconds. You just have to be patient and observe the double for a long period of time. I've sometimes stared at a double for over ten minutes before a moment of stillness allowed me to see an elusive fainter companion.
As for the required magnifications, I know that for targets like Ascella (0.5 arcsec) for example I need well above 300x to detect elongation, looking best at 600x in my 6-inch.
Extreme magnifications require high quality optics, spot-on collimation and a solid tracking mount. I would probably find it way too hard to use 300x or above with a hand-nudged Dob.
Cheers
Steffen.