Got some strange viewing going on in my scope

[acharris77]

Hi all, I need some advice. When I looked through the scope last night after letting it cool down, I did my goto alignment with my 25mm ep and when I centered Sirius in the eyepiece and focused it, it looked quite formed and sharp with diffraction spikes and looked concentric slightly out of focus. Same again with Alderban(sp) as my 2nd alignment star.

Went to the M42 and could see the trapezium with the 10mm seemed ok. When I sent the scope to Mars, I had what looked like Mars bright in the middle, then a gap and another thin ring around the outside, like a coma (think that is the term, still learning).

And also depending on how I looked in the eyepiece, I would get it slightly left, elongated but never a good view of mars. I know it is bright and washed out, but I used my meade filter to try and dim the view, though my meade filter is rubbish I think as it is not a ND96, but one I bought from ebay.

Do this sound like a collimation issue, or is it cause the scope was pointing quite straight up, and I was looking at a strange angle. as I have not worked out yet the good viewing position at an steep angle. Could this be possible or does it need collimating??

Thanks.

[Doc]

I had this problem with Mars last time I observed and your description seems spot on, my scope turned out to be slightly out of collimation.

Stars seemed pretty good but Mars just seemed to be slightly fuzzy and I was unable to get a sharp view, even though Mars was pretty high in the sky.

But then insufficient cool downn time might have the same effect also looking through a murky atmosphere.

[John]

Warm air currents in the scope can also throw up some odd effects. On the really cold night I find these currents take ages to clear. On the coldest night we have had I could even see my own heat plume in the light path as I stood next to the scope - difficult to avoid that unless you are a zombie !.

[davetee]

probably moisture on the lens

[lmao_37]

i have had similar problem with my scope when i was observing jupiter a month or two ago and what i think it was over magnification for the seeing conditions as when i went to a lower mag the problems went away

[acharris77]

Thanks for the replies, it probably was something to do with the seeing conditions and tube currents, maybe I will have to leave it a bit longer on these colder nights to see if it helps. Anyway looking at the forecast Thurs, it is going to be clear, so if everything goes well I am hoping to get out at around 18:50 and try and catch some images of stars and hopfully the M42, as since I have got my camera we have only had 3 good nights, so not really got to grips with DSO imaging yet.

Plus the last few good nights we have had the last week or so I have been really busy and not had time to get the scope out, too tired from being flatout. Thanks again for the help.