Quote:
Originally Posted by 209herschel
And how big in the ep of a 9mm GSO plossl. I'm just trying to get an idea of what to expect. Thanks again.
|
Current data for Saturn courtesy of Stellarium:
Apparent diameter = 18.2 arc seconds. with rings = 42.5 arc seconds.
Our Moon is typically 1800 arc seconds (1/2 degree). Have a good look at the Moon unaided, i.e. no telescope or binoculars and see what detail you can pick up.
Now your telescope is 254mm, f5 so focal length = 1270mm.
Magnification with 9mm eyepiece = 1270/9 = 141x.
Multiply 18.2 x 141 = 2,566 arc seconds. (1.4x bigger than lunar disk)
Multiply 42.5 x 141 = 5,992 arc seconds. (3.3x bigger than lunar disk)
As you can see a 9mm eyepiece in your telescope will give you an image of Saturn bigger than the Moon unaided. You should easily be able to see banding on the planet (much more subtle than Jupiter though) and of course the Cassini division should be evident as a think dark 'gap' in the ring plane about 1/3 from the outer edge. In fact your telescope should also reveal the much thinner Encke division (close to the outer edge), but only under very good seeing conditions.
As for collimation, have a look at the bottom of this web site for some diffraction ring images:
http://www.willbell.com/tm/tm5.htm
As long as everything is concentric you are collimated. Note start with a medium power eyepiece and then go higher. The higher the power you can get concentric rings, the better the overall collimation. Check both inside and outside of focus.