Quote:
Originally Posted by el_draco
... I'd be concerned about an overly high pier due to resonance and flexure issues.
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Quote:
Originally Posted by troypiggo
G'day. I'm curious about the "resonance" - what's causing it, and how does it affect imaging? Is it from the mount motors during a slew? Focus motors? Ground vibrations? Wind?
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Draco^ is on the money. The longer the pier the lower the natural frequency of oscillation. And the lower frequencies can be much harder to damp or reduce. These lower natural frequencies are often excited by footfalls or any inadvertant knock/bump/low freq vibration in the area.
Broadly speaking, for a simple column (well vertical cantilever with uniform loading and no point load
) doubling its length without any changes to its cross section or stiffness, will decrease the natural frequency of oscillation of the structure by a factor of 4, making some vibrations very hard to damp or attenuate. As to how that all effects the image, well it certainly could if there is ground borne vibration or wind loading on the device or structure, not to mention footsteps. Surprisingly even a constant wind can cause / excite vibrations. Maybe it's just inbuilt dithering (not really
)
Best
JA