Hi all.
I recently picked up a used Orion XT10i. I managed a quick session on it between the clouds up here and the collimation was ok. I knew the primary mirror was rather dusty so, with all the cloud, and because it was niggling away at me, I decided I would dive in and give it a clean. I carefully cleaned it and rinsed it with distilled water, and, pleased with the result, popped it back in the tube. I aligned it with a laser collimator but on my next session found the stars to be quite blurry. Time to learn the whole collimation process I thought to myself. I made myself a collimation eyepiece by popping out the lens from an old H8 ep that I dont use, put some paper opposite the focuser and blocked off the primary with a piece of card. To my puzzlement the secondary was way off toward the tube opening, and a little elliptical too. I've adjusted the secondary to what I think is, by eye, nicely round and central below the focuser. I got a second opinion on that too. The primary has again been aligned by laser. Wen viewing down the focuser, the primary image is rather off centre to the focuser but all the mirror clamps are visible. All well and good I thought. Unfortunately things are not quite coming to crisp focus. Jupiter had a milky, slightly off centre "glow" to it. Bright stars when slightly defocused have a kind of spiked double comet tail effect, both tails going in the same direction but about 30° apart. The eccentric aura round Jupiter was bulging in the same direction too.
So in summary:
To my inexperienced eye, it looks to be collimated ok but doesn't pass the star test.
It was ok before I took out the primary despite the secondary being noticably off.
My questions are
Does that comet tail effect point to a specific problem?
How could it have been passsing the star test with the secondary being off centre to the focuser?
Have I screwed up the mirror somehow?
Any answers, comments or suggestions would be very welcome.
Thanks.