More Tweaking with PEMPro

Well last week I spent another few hours out in the POD doing an upgrade to the imaging setup and re-doing the polar alignment and periodic error correction of the mount.  From the previous run with PEMPro, I could see a large improvement, but I felt it could be better.  After polar alignment, my first pass with PEMPro showed an uncorrected periodic error on the order of +/- 25 arcsec.  After calculating and loading the correction curve, with PEC turned on, I was seeing about 10 arcsec pk-pk tracking error.  Respectable, but not as good as I wanted.  Previously I had the EdgeC11HD installed with a dovetail on top so I could slide on an 80mm APO for guiding and widefield imaging.  However, because of the design of the POD, having the guidescope on top of the big C11 resulted in too many times where the dome half would totally block the guidescope.  So I decided to do a side-by-side arrangement of the two scopes.  This would help with the blocked scope issue but what about the PEC?

After thinking things thru, I realized that in initially trying to dampen out mount vibrations with very large metal washers and high durometer silicon washers/bushings, I actually introduced a small but significant degree of flex in the whole mount that would change depending on the position of the scope.  Out came the bushings, the mount base was re-levelled and the mounting nuts were tightly snugged down to the pier bolts.  The mount was noticeably more rigid now (and I really don't have to worry about vibration anyway, as I have a wooden pier, rather than metal or concrete - both of which make great lightning conductors!)

I picked up a side-by-side mount from ADM and installed the C11 on one side and my slightly larger APO refractor - an Explore Scientific ED102 - on the other side.  Next I carefully balanced the two scopes in reference to their mounting center and the two mount axis.  Once darkness fell, I fired up everything and did a quick 2+4 alignment (2 alignment stars plus 4 calibration stars.) Next I re-did the polar alignment adjustment using PEMPro and got it down to less than 1 arcsec of error.  I ran thru the PEC measurement and calibration and when done, had a total pk-pk periodic error of just under 3 arcsec!  Hoorah!  Patience and nit picking paid off!  Most $5k to $10K mounts don't do that well out of the box - and mine cost way less than half that.  Thank you Lord!

I'll post a picture or two of the new scope / mount arrangement this weekend.  Needless to say, I am quite happy with the mount tracking accuracy.  Next I have to install MaxIm DL 5Pro Suite with MaxPoint so I can refine the go-to pointing accuracy (although it is already much better now that the PEC has been further refined.)  The saga continues...

Peace & blessings!  Donn