Thanks John for chiming in.
my apologies if so lengthily!
Below is a more detail description that Robin suggested. Now I mainly wrote up a step by step conception, using multiple eyepieces and users, when one changes out an eyepiece for more or less power on a telescope, refocus is necessary.
You are correct about backlash, however with my (SCT) Schmidt Cassigrain Telescope the primary mirror will be set and a fixed postion to eliminate backlash or mirror shift. and allowing my secondary crayford focuser by JMI NGF-S and has a DC motor on it to do the work. I would be replacing with a stepper, the overall torque is minimal and can figure out its torque and overall travel, just need to be very slow.
There may be 10 other ways to accomplish this in a more simplified fashion, but this is the best way I know how to describe it right now. I hope this helps.
Kendall
This example demonstrates using 2 users and 2 telescope eyepieces without touching the telescope focuser
Step 1
User places the #1 eyepiece in the telescope.
Step 2
Power on the focuser/project, and focuser moves to limit switch and stops.
Step 3
User #1 presses and holds the eyepiece #1 button, button or an LED flashes. (program mode)
User #1 also presses and holds the user #1 button and the button or an LED flashes. (program mode)
Step 4
User #1 moves a set of up/dn buttons to move the focuser for object to be in focus.
Step 5
User #1 presses one of the 2 flashing buttons to get out of program. (the 1st user and 1st eyepiece are now programed.
Step 6
User #1 removes the #1 eyepiece from the scope and replaces with eyepiece #2 and repeats steps 3 – 5.
Now eyepiece #1 and #2 are set up for user #1.
*For the 2nd user: they would complete steps 3-5 using the #2 user button.
When initial set up is complete:
Example: We start using the 1st eyepiece (#1 eyepiece) user #1 presses the #1 eyepiece button and his user #1 button and looks into the eyepiece and should have a focused object, and the next user #2 wants to look at the object, he or she would just press the #2 user button and looking into the eyepiece and it should be in focus for them. Next, if we are to change out the #1 eyepiece to the #2 eyepiece, the user will press the #2 eyepiece button and his or her user # button and the object should be in focus.
This system would have 4 channels instead of the two mentioned herein. Representing up to 4 users and 4 eyepieces.
There may be work around with this configuration like a central program button. It would be nice that the user and eyepiece buttons would light up in there perspective mode to show where the focus is.
The programs can stay in the system until power off or over write, restset or what ever would work the best.