Read the article I linked. According to Roger, all of Canon's newer lenses, dating as far back as the 70-200 f/2.8 L II I think, have rotation detectors.
Oh, I've read it - including the part where you seem to have missed the 10 year difference between when you suggest rotation detectors were incorporated, vs. when Roger does, or maybe that's a typo on Roger's part...but it makes me wonder what was going on for those 10 years...Quote from: Roger CicalaIf this is the case, then the newer Canon lenses should definitely have a rotation detector built into them. We know there are rotation detectors in many lenses released after 2000, but if they are in older lenses we can’t identify them, so this fits too. (As an aside, I am particularly skilled in finding them because usually if you touch them with your fingers the lens won’t focus anymore and the unit has to be replaced.)
I did see that they had rotation detectors in lenses dating back a decade. However I also only saw that it seems more recent AF systems (lens+camera) use a closed loop, or at least a partially open loop. Older systems still used an open loop, and I suspect some kind of partially open loop when a new camera is used with an older lens that isn't quite up to snuff (although were exactly the cutoff is I really can't say.)
A Phase Detect System for all manufacturers operates as a limited closed loop, but that only assures that the lens tells the camera that it has moved where it was told to go.
This was my point earlier - the closed loop is 'look-move-confirm' but not 'look-move-confirm-look'.
Hmm, that is not my experience. And in one of the articles in that series Roger posted, he clearly stated that the AF system seems to fully adjust the lens as necessary in a single press of the AF button in single-shot mode to fully lock AF. His expectation was that it the AF system only did "look-move-confirm" rather than "look-move-confirm-move-confirm" that multiple presses of the AF button would further refine focus. That was not the case. AF was fully and precisely locked the FIRST time, and all subsequent attempts to AF resulted in no change...but only with the latest gear...i.e. a 5D III with one of the new STM lenses, or one of the new Mark II Great Whites. Older cameras still seem to operate on a partially open loop.