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Can this resonance be baffled by adding strapped turnbuckles? -Best, Robert
On 05/26/2021 2:54 PM Don W <westergren@...> wrote:
Ringing (like a bell) is never a problem - it is a high frequency / low amplitude motion that never is seen by the scope. Ringing is started with a bang, which you will be VERY unlikely to do. You don't hit your pier with a hammer do you?
Stiffness of a pier is very important if you are visual observing and want to manually focus on Jupiter - just touching the focus knob can move the object and set up fundamental oscillations (primarily of a cantilevered pier - mounted on concrete). A tripod or AstroPhysics portable pier with a wide doesn't have this problem. But a metal pier bolted or inserted into concrete is a spring ready to wave back and forth. Putting anything inside a tube (sand or concrete) is a disaster waiting to happen - adding mass to the spring and causing a very long oscillation lasting for seconds.
If the pier is used only for imaging, these concerns for oscillation are much less a problem, since only wind is likely to affect the bending of a tubular pier. For these type piers, the difference in stiffness between aluminum and steel is 3:1. The modulus of aluminum is 1/3 that of steel, meaning the aluminum is far worse.