My 70-200mm is not parfocal - ie. focus changes as focal length changes. At 70mm infinity is actually at 10m on the distance scale, while at 200mm infinity is infinity. It went to canon last year to get calibrated and has come back nice and sharp, but this behaviour does seem very strange. It does mean I cant focus on something at 200mm and then zoom out to frame.
DavidP wrote:
It's supposed to be (per Canon's Chuck Westfall).
And, it's reasonably close.
But upon really close inspection, it's not parfocal.
I agree that Chuck Westfall has stated several times, here and elsewhere, that the 70-200mm is parfocal. If I recall (and maybe you can comment on this) he stated that it was only parfocal in one direction. That is, if one zoomed to 200mm, focused, then zoomed back to some wider focal length, focus was maintained (as long as you did not refocus), but going the other direction it was not.
I also think he used another term to describe this behavior other than parfocal in one of his papers.
Here are some links to the issue that include comments from Chuck Westfall:
I just tried this, trust me focus-zoom-refocus is sharper than focus-zoom to compose.
I don't care what any links say, try it for yourself. 70-200 f4 IS and f2.8 IS. It's not alot
of difference, but it's there nonetheless with my copies and I doubt I'm the only one
trenchmonkey wrote:
I just tried this, trust me focus-zoom-refocus is sharper than focus-zoom to compose.
I don't care what any links say, try it for yourself. 70-200 f4 IS and f2.8 IS. It's not alot
of difference, but it's there nonetheless with my copies and I doubt I'm the only one
I agree. I've tried Westfall's suggested technique as well, never had it work as described, and always assumed it was something I was doing wrong. Either that or there was something wrong with the lens. Since the lens is superb in every other aspect of operation I just ignored this issue.
its probably considered parafocal in the CoC, but you can get a better image with refocus, i noticed this was exaggerated with an aftermarket 2X, but the Canon 2x does help (still needs Some refocus, but not as often/much)
Jane_EOS wrote:
I agree. I've tried Westfall's suggested technique as well, never had it work as described, and always assumed it was something I was doing wrong. Either that or there was something wrong with the lens. Since the lens is superb in every other aspect of operation I just ignored this issue.
Jane
Nice Canon "store" you've got there Jane. I'd get a headache tryin' to decide what
to shoot Canon really got this one right, didn't they?! Apologies to the OP for the OT
trenchmonkey wrote:
Nice Canon "store" you've got there Jane. I'd get a headache tryin' to decide what to shoot Canon really got this one right, didn't they?! Apologies to the OP for the OT
The guys at Samy's Camera have my customer number memorized.
Canon really got this one right, didn't they?! Apologies to the OP for the OT