focus problem or just bad seeing ?

[vindictive666 (John)]

gday all

we went oustside lastnight and had a peek at saturn it wasnt that low at the horizon had a look at 155x mag no problem getting it in focus however we barlowed it 2x and it wouldnt really focus and i was wondering if that could be a problem with the scope (we Collimated it last night aswell) or just to put it down to seeing conditions? i realise it could be a number of things but any theories ?


plus it moved out of fov rather quick as well. jupiter was cool last night was impressed with the grs as well as the transit of europas moon cool sight
plus iam still getting a smidge of tails on jupiters moon. i checked the secondary for "pinching" seemed ok so i suppose it could be the primary ?

any thoughts ?


ps forgot to try jupiter

[ving (David)]

when objects are low on thehorizon you are looking thru a hell of a lot more atmosphere. in there lays you problem with saturn i am guessing considering that jupiter (much higher in the sky) was ok.

[atalas]

310x in a 12" newt ! put It down to bad seeing mate.


Louie

[mch62 (Mark)]

Forget trying to view any thing 30degs or lower from the horizon as you are looking through so much more atmosphere and heat haze.
The best time to view with high power on the planets is when they directly or close to it above you.
Another thing to realize is , with a Newtonian to keep the object centred in the field of view.

Newtonian's suffer from an aberration called coma which causes stars to flare the further away from the centre of the FOV.
The actual area of well corrected FOV on a Newtonian is only very small as in only a few millimetres and varies with the focal ratio of the primary.
The further from the center the less contrasty the image becomes and stars and small moons will grow little tails or sea gulls is another term used.

So to get the best planetary viewing keep the planet centred and best up above 30degs from the horizon.

[Starkler (Geoff)]

For me the nights are rare where I could use 300x , and certainly not with an object low on the horizon.
Why not check the mounting of the primary as well ? Its not a difficult task assuming you have the tools to recollimate. Almost always gso clamp their primaries down way too hard.