Quote Originally Posted by Kiwi7475 View Post
Right, right, Dan, I’m not saying the mechanism is the same, I’m asking whether the shutter opening slowly relative to the overall shutter speed (eg if it takes 1/1000 to open and 1/1000 to close and you selected a 1/500 shutter speed, such that the aperture has just enough to open to open and close, rather than offering a large fraction of exposure time being fully open) isn’t but in fact another mechanical vignetting effect — different from the one you mention (now induced by the shutter creating the vignetting) but that in fact compounds with it when you shoot wide open at extreme shutter speeds.
Thanks for asking again. You're concerned about shutter efficiency, which has been addressed well earlier in this discussion.