It depends on the model of the focuser. It's much easier to make a helical focuser that turns everything downline from itself, but it is possible to have one that does not.
Depending on the specific focuser itself, you may be able to actually put the device after your diagonal, etc., and just turn the eyepiece. There are focusers of this design available as well, I believe.
There are also crayford focusers that can provide smooth and very fine focus capability by use of vernier reduction drives.
Depending on the specific focuser itself, you may be able to actually put the device after your diagonal, etc., and just turn the eyepiece. There are focusers of this design available as well, I believe.
There are also crayford focusers that can provide smooth and very fine focus capability by use of vernier reduction drives.