PST concerns

[Rob Severn]

Hi all, I've had a PST for a while now and have recently noticed that I have to move the part of the sun to see the prominences on into the centre of the fov I have to sort of swirl around the edges and the prominences pop into view, there seems to be some sort of coma effect it's reasonably ok with eyepieces of 20mm and longer but very noticable from around 14mm downwards. It's the same with surface granulation the full disc is never fully resolved just a small circular area. Does anyone else have this or is this normal never having looked through another PST ? Also the tuning ring is able to move up and down the tibe by about 4mm, it was like this when I purchased it, should it be tighter ?

Thanks

Edit: The last question is probably self explanatory, it probably shouldn't move, any ideas on fixing it