So for focusing you first achieve coarse focus using an initial step size of 100 and then you start from that focus position and repeat with an initial step size of 10?
Wow, I did not know that the RASA was so finicky. Refractors are so much easier to handle and more forgiving is so many respects then.
If I understand you correctly you are seeing the same thing with the curve first going upwards and then downwards and it taking more than the expected 5 steps to reach the minimum.
I am seeing the same thing. I visually confirmed that the focus motor moves out and then moves back in again to clear the backlash before the focus run starts. Nonetheless, I think the distance it moves out should be adjustable, because the load on the drawtube moving out is lighter than when it moves back in again against the resistance of gravity.
F(o) is not equal F(i) where F(o) is the force the motor must overcome to move the drawtube outward, F(i) to move it back inward, with F(i)>F(o) as F(i)= Friction+Gravity and F(o)=Friction-Gravity.
So the motor has to perform more work, but the energy input (V x A x t) remains the same (for my analog focuser, at least, not necessarily for a stepper). So with the same amount of work (W) performed by the motor and time t being constant (invariant step size) and W=F x d, with d = distance the drawtube moves, d will be different for outward vs inward movements.
d(i) not equal d(o).
Therefore, more than the 5 expected steps are needed to return back to the minimum. as more steps are required to perform the required work. Just as Newton and Maxwell would have predicted.
Therefore, it would be great if the initial number of steps could be made adjustable to allow values other than 10, depending on how different F(o) and F(i) are. This number will vary from user to user and telescope to telescope, so it should be user adjustable.
Does that sum it up for you as well, Doug?
Other than that, Linear is one hell of powerful focusing algorithm!
Kudos to Hy for that great contribution.