I have found that focus shift confuses people.
Michael Erlewine writes about focus shift in reference to the GFX 120/4 tests:
If I understand properly, in manual focus, if I focus once, shoot at different apertures, and then examine them, the focus should be the same, aside from varying DOF?
If I understand you right, this problem is not just about autofocus, correct? I never use autofocus, for example. This affects me of course, whether I keep the system, the lens, etc.
DIGLLOYD: focus shift has nothing to do with autofocus vs manual focus. It is an optical behavior. It occurs with lenses from super wides to telephotos, and in some cases is used as a balancing aberration. I consider focus shift one of the most abused tradeoffs in optical design (wide angle lenses often need a little of it, no excuse for longer lenses), a tradeoff that is frequently unacceptable because accurate focus is the #1 determinant of image sharpness.
See Focus Shift and Spherical Aberration in Making Sharp Images as well as various articles and posts on focus shift on this site (that list is just partial, due to partial indexing, search for focus shift).
For real-time see-with-your-own eyes: “Video: Focus shift with the Zeiss 85mm f/1.4 Planar” under Challenge #5 in Focusing Zeiss DSLR Lenses For Peak Performance, PART ONE: The Challenges, also shown below for convenience.
Be sure to view at 1080p.