Gene51 wrote:
And the final fact is because internal lenses shorten the focal length at the minimum distance, so in effect it is not the same focal length. This is called focus breathing, and is usually not an issue unless you are focus stacking using the focus adjust method, which would change the field of view, as opposed to the camera position shift method which does not.
It would take forever to find it, but quite awhile back someone here said they found that an internal focus lens only reduced the working distance by about 25mm versus an external focus lens. I think he was comparing 2 different Tokina 100mm macro lenses. At any rate, I agree that the only real concern might be when focus stacking.