Options for Solving Vibration Problems
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If you have some of these problems, you can take steps to improve your observing. Some are simple, and some are complex. They include the following (details will be discussed below).

• Accept some vibration, and limit your observing in accordance with the quality of your system. For example, if wind causes vibration, do not try to do high resolution work when it is windy.
• Use active feedback to correct the image shift electronically. While we do not discuss these methods in this book, they are entirely feasible for visual, photographic, and CCD imaging.
• Construct a pier and mount with extremely high rigidity. This ensures a high frequency of vibration. For a given Q, vibration will die out more quickly. High rigidity also tends to imply a smaller amplitude of vibration resulting from a particular excitation. High rigidity can be achieved by using rigid or stiff materials and shapes in the mount, including the use of triangular bracing. Reducing component weight, and designing for minimum moments of inertia by keeping masses close to points of supports, also increase the natural frequency. This is important because simply adding more steel to a mounting may make matters worse. More strength may increase the frequency of one vibration mode, but the increased mass may reduce the frequency and increase the problems from other vibration modes.
• Construct a pier and mount with very low Q, i.e., high damping. This requires that you design the system to dissipate rapidly the energy of any vibrations of concern. Filling hollow components with sand is a common method. However, the use of more sophisticated materials including lead or rubber and plastic bonded to the vibrating components can also increase damping.
• Prevent perturbations and exciting forces from reaching the system, so that vibrations do not develop. This approach includes use of electric focusing (so that one does not touch the telescope as frequently), use of a well designed dome to shield the system from the wind, and isolation of the pier from the surrounding environment.
• Design a pier system that tends to respond to perturbations by translation, rather than rotation, thus reducing the resulting image shift.

Many observatory and pier installations combine several of these approaches, except for the last one which has received little attention. However, the designer must be aware that "everything is connected". In evaluating an existing vibration problem, one must pay attention to the pier itself, what the pier is connected to, the mount, the telescope, and all other parts of the observatory. Likewise, if problems are found, the solutions may affect more than just one portion of the support system.

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