focusing 250 dob

[yoda]

Hi all the outher night I was looking at saturn at 120x (10mm EP) allthow still looks small I coud see the rings and possably three moons,so I uped the power uesing a 2x barlow and coudn't focus propley. so I got the Collimator out and that is spot on, 240x is only just over half the power of the scope. Any ideas thank's a lot all the best.

[Moonshane]

assuming the scope was cooled for about an hour I think there are two likely options:

1) the seeing was not good enough to accommodate 240x (common problem in UK). you can get around this to some extent by waiting for occasional good seeing every now and again but it's fleeting and may never happen on some nights. this is effectively what your webcam and processing does.

2) the eyepiece and barlow combo was not of adequate quality to perform well in your fast scope.

apart from the moon and occasionally double stars, the chances of more than 250x in the UK being usable on planets are remote or at least infrequent.

hope this helps a bit.

[yoda]

Thank's Shane saturn was quite low, alltho M3-NGC 5272 globular cluster was lower and that looked great.

Sorry my bad m3 was higher.

[Moonshane]

likely to see seeing I reckon, especially as when low you are looking through even more atmosphere.

[Chris H]

Can only backup what Shane has said, I have a 5mm ep for use in my 10" Dob I've probably managed to get fleeting clear views with it on two occasions in the last six months. Think of your Dob more as a light gathering scope rather than just a magnifier.

[yoda]

Great stuff thank's guys.