Polar Alignment question Stefan Berg Nighttime Imaging 'N' Astronomy (N.I.N.A. / NINA) · Keith Geissler · ... · 29 · 1202 · 3

I have been using 3PPA for many years because Polaris is hiding behind my roofline. I even have it in my start up sequence in NINA and it repeats 3 times from the home position. In the first run I dial it in below 30", than back home. In the second I go to below 10" and back home. And in the 3rd run I check where it lands. If close to 10" I leave it there. Otherwise I make a little adjustment. One thing is to start 3PPA away from Polaris and I use the same location throughout the procedure plus I do it relatively fast. I usually do not need more then 20 seconds to dial in each time. The more time taken, the less accurate PA ends up to be.

Now, I know people have their favorite PA tools they swear upon. I do have Sharp Cap as well and a "third" one. At my second location I do have Polaris visible and 2 years ago I did once run a test with all 3 systems. They are all good if you can see Polaris. Is one more accurate then the other? In my opinion, No. And I stopped paying attention to PHD2's Guide Assistant polar error value. I had it more often show large error values when on the other hand during imaging, guiding returned constant RMS of 0.5

Nina's 3PPA has been notiously unreliable for me, and quite a few of my friends. 

I switched to Sharpcap about a year ago and have never had an issue since, plus it's much quicker.   My PAs are dead on.

Keith Geissler:
How many times before I start imaging, should I run the polar alignment?  I usually do once.  I try to get it under 1'.  I will then notice my guiding is off, so I will move my mount to the home position, run the 3PPA again, only to see it is off.  

Why the discrepancy between alignments?  Do I need to run it multiple times?  Sorry for the beginner question.

If on your first 3 point polar alignment  routine you are off by more than say 50´ on either axis, finish the first run and then repeat. Once you are well below 50´ on the very start of the routine, finish that round and you should be good to go. As I am in the southern hemisphere, sometimes I do not have a good reference starting point for my polar alignment. In those cases, when I start the polar alignment routine in NINA, I am usually 2 to 3 degrees off the pole . I repeat the polar alignment routine a few times as I get closer and closer to a good  starting point and repeat the routine from there. It works great and end up with almost perfect alignment.