Non-linear Rack Focus velocity (for smooth organic focus change)

[Rush]

This feature's goal is smooth rack focus velocity for more organic look.

Current rack focus velocity is linear so transition it makes is not smooth.

But focus transition can be smooth if focus speed will vary – fast at start and slowing down as rack focus reaches its end point.

It can be achieved by adjusting “step size” over time – starting with biggest step size and slowing down to smallest step size as it reaches end point.

I know that current rack focus implementation don't know where it's end point - it simply changes focus defined number of steps. Is it possible to have rack focus which is based on memorized focus distance?

(feature idea by http://vk.com/onichan, not me)

[a1ex]

Focus distance is pretty rough - maybe it will work best combined with step counting (with some sort of Kalman filtering or similar sensor fusion algorithms).

There are only 3 step sizes, so I think it's better to vary the delay.