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Focusser "smoothness" v's flop
Changes to the thrust bearings, and focussing knob system, will not make any real change to the mirror movement along the baffle, there's still potential for the mirror to flop sideways.
The focuss rod is usually at three o'clock looking at the rear cell, it therefore ( and the use of the "locking screw" method) can ONLY affect the flop in the 3 to 9 o'clock direction, in the 6 to 12 o'clock etc there's nothing preventing the mirror from tilting and hence giving image movement during long exposures. I'm not to worried about some movement during focussing, it's when you 're guiding and taking a long exposure photo that it can and does become a headache.
Note when mounted on a wedge the 3-9 o'clock is usually the RA direction ( good news!) but the 6-12 is the Dec and the off-set loading of the mirror will vary with altitude.
Members with the R series telescopes which also have the "improved" locking collar around the baffle, still say mirror flop is an issue.
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