Good points there AndrewJ.
I ran some simulations on my pier based on my locale's design wind speed (of 33m/sec, which equates to 118.8kph, and 700 pascals). My pier design is 1200mm high x 165mm dia PVC pipe with concrete fill & 3 x 12mm reinforcing, integrated into a 750x750x650 reinforced footing in M class soil.
At the top mounting plate I had maximum deflection of <0.25mm. Now this is assuming that the foundation is not moving in the ground, and it's blowing a gale, and everything is rigid. It was from here that I concluded that a lot of what I've read about pier design is over the top.
The "weak" points are going to be the footing in the ground,
the pier to footing interface (in my case it's integral), the mount to pier interface, the mount itself, & the scope to mount interface. You need to know what might induce vibrations & where they will emanate from, and counteract them specifically.
The #1 culprit (IMO) will be intermittent wind gusts - A wind speed of say 40 kph gives you a wind pressure of around 70 pascals, which is nothing. That's pretty windy though. I'll be packed up and inside watching telly if it's up at that.
Fast slewing of an out of balance scope and mount can induce some movement which can resonate for a moment when the mount stops.
Chris, I did a sim on your design, assuming a base plate dimension of 16" square, and came up with nearly 0mm deflection at the top of the tube with 1 Mpa wind pressure. I wouldn't stress (so to speak).
