I would like to build a camera mount that could track stars for up to two hours. It would be a simple pair of levers, one being fixed to the tripod and the other attached to the camera. The axis of the pivot would be aligned with true north and a screw mechanism would push the levers apart, like scissors opening.

Driving the screw at a constant speed will allow exposures of several minutes, but eventually trig errors start changing stars into ovals.
Ideally, the speed of the screw would slowly decrease to compensate for the ever changing geometry. What makes it really complicated is the rate of deceleration is not linear.

There is a commercial unit in existence, so I know it's possible.

Are there any math gurus that can come up with a solution?

Mike

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