I mounted the original stalk (an aluminum cylinder with elliptical slice at one end and threaded hole for center screw at the other end) in the center of the new mirror. I was pretty sure that stalk was mounted in the center of the old mirror.
However, when I installed the assembly onto the spider, I couldn't get the mirror completely centered under the focuser. The stalk is slam up against the spider with only just enough room to collimate the mirror, and the center of the mirror is maybe 3 mm below the center of the focuser.
Tried the scope out Saturday night. The seeing was poor with too much sky glow. I only got a glimpse of Jupiter before it vanished behind the house. Saturn was a white blob with wings, though at one point I was able to resolve it into a sphere with one big ring around it. Still bright white.
The stars were tack sharp, especially in the 24mm Pan. The sky to the ENE was velvety black scattered with diamonds. It was quite beautiful to look at, but there were no objects in that area above the horizon to try to view.
So my question(s) -
Regardless of the change in major or minor axis size, the center of the mirror is the center. If the stalk was mounted on the center of the old mirror, the new mirror should line up under the focuser the same. The only thing I can conclude is that the stalk should not be attached to the center of the mirror. The original mirror had an offset of 3.048mm. Does this mean the center of the stalk should be attached 3mm below the center of the mirror?
I used aquarium sealant to attach the mirror to the stalk in an effort to avoid off gassing issues. Is there an adhesive that is preferred over aquarium sealant?
The stalk is pretty small, and I have a hard time getting three distinct dabs of sealant on there. The original mirror was attached to the stalk using double sided foam tape. It held just fine for several years. Should I consider going back to foam tape?