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Hi Marcel,
Many years ago, before my observatory went two storey, I was visiting Coonabarabran. The Sky Watch Observatory was in the throws of being built, the pier for the scope that was to be installed in the dome was in position.
It surprised me that the pier, which from memory was about 8 or 10 inches in diameter was filled with sand. When I tapped it with a rock it rang, not like a bell but clearly resonated.
When my observatory increased in size and went two storey I obviously required a pier. I have an engineering background and used 8" pipe for the pier. This pier is in in it's own separate plug of concrete that extends 4 feet into the bedrock, it is totally isolated from the concrete of the ground floor with strips of 1" thick polystyrene separating it from the main concrete floor.
I have 6 lengths of steel twisted reo, wired together that run the full length of the pier. The pier is filled with concrete. It is extremely rigid and even when hit with a hammer does not ring or resonate in any way.
I have a 16" F4.5 Newt on a very heavy German Eq mount bolted onto this pier. I regularly post my planetary images on IIS, these are captured with a DMK 21AU04 using an Orion filter wheel.
Obviously to get colour images I have to capture R, G & B channels and to do this I must physically rotate the filter wheel. I have my Laptop on a computer table beside the scope and as soon as I rotate the filter wheel and release it the image, at very high power on my screen, stabilizes instantly.
I can only speak from my personal experience based on the quality of the images I produce and the stability of the image when I do visually observe through my scope. I am very happy with my concrete filled steel reinforced pier.
For your interest I have attached an image of the pier, note the polystyrene strips separating the piers concrete plug form that of the floor. Also an image of what is mounted on the pier.
Regards
Trevor
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