I have a year 2000 Nexstar 8 (grey tube) on and HEQ5
F6.3 reducer, 105mm back focus to a Canon T3i
Collimating with Vega which is near zenith for me.
Got this scope 2 months ago.
When I initially tried to collimate it, one of the screws was about as tight as it will go. It just so happens that this screw corresponds to where the dark center ring during collimation is closest to edge
I have been trying to get this thing collimated, so last night I tried to reset everything and tightened all the screws (not with brute force just trying to get them all to a standard starting point) and then loosened them all a couple of turns. The image below was before I did this adjustment. In the image below it is Oblong. I was able to get the circle center in the light field but the oblong shape never disappeared. So then I tried to bring it into focus and as I did the oblong shape seemed to get worse or atleast didn't go away and the dark center circle started to drastically shift to one side of the light field of the star. Once I get the scope as in focus as I can , the stars look like they do in the second photo. The stars in the second photo are how they have always looked since I have had this scope. I would describe it as oblong circle with the brightest point to one edge of the oblong circle. I would say that the bright point on the oblong stars is where the dark center point during collimation is heading to.
The focuser on this is as smooth as butter, if that matters.
Any thoughts would be appreciated. I haven't given up hope that it is just bad collimation but the oblong nature gives me some concern and also concerns me how the center shifts during focus. Also, during this colimation I had it 3 turns out of focus, don't know if that matters, I've read to just do one turn out of focus and zoom in.