Mars in not a comet...

Hello all
I just got a brand new ETX-90 OTA that I'll use as a guide scope, but the first night out was a bit of disapointment.
I pointed to mars, that was almost overhead, and instead of seeing a disk I saw a comet like image. I could see the disk alright but there was a big V-shaped "tail" coming out of it.

I then pointed to several bright stars and the problem was still there.
If I use a high magnification eyepiece, things get much worse.

I guess this is a collimation problem. The problem is how to collimate the ETX? I did a search on the web, but only found intructions saying NOT TO try to collimate it.

Any suggestions?

Thanks
Alex

take it back

I certainly wouldn't take it back just yet. It sounds like a textbook case of a heat plume.

Was the scope thoroughly cooled down to ambient temperature? Often beginners aren't even aware that this is necessary, but particularly as the weather this time of year gets colder it will make a huge difference. A Maksutov like the ETX also cools slower than other designs because the corrector is so thick. If you take it directly out of a warm (relatively, at room temperature) house into an autumn night in most climes, you are almost certain to have bad images for quite some time, with what you are seeing being among the most common problems when the scope is much warmer than the air.

Try setting your scope out at least an hour before you plan to use it and perhaps as much as two hours depending on the difference in inside and outside temperatures and whether and how quickly the outside temperature is dropping, which it will usually be doing around dusk. If the scope thoroughly cools to ambient temperature and still shows this problem, then it's time to think about returns and the like - but I'd bet it won't.

Sounds like coma to me!
Floyd