Perry Ge wrote in post #7671348
Mine did that too. It was pretty schizophrenic and would often readjust focus slightly after initially acquiring it.
Mine also focus shifted. Front focused at close distances, backfocused at far distances. Not that my 50L doesn't focus shift either though
(but I'm much happier with it, it doesn't affect real world shooting
, I only notice it when shooting charts and boxes, which is not often).
Why do we say that about the 50L, to me, that's just part of the story Perry. Perhaps it doesn't bother you because you're shooting stopped down and that's fantastic that it suits your style so well, you do great work.....But many of us tried to use the 50L in "real world" shooting which for me (us) is usually f1.2-f2.8 with a high aperture 50mm....I shoot a lot of still life but in the 3' to 7' range. So the 50L is just out of question... (BTW, charts are the last thing I shoot when I notice a problem...hate shooting charts ) Anyways....That's why I find the EX such a breath of fresh air....Doesn't matter what aperture I shoot at, from any distance, it just works...very nice.
I realize there are a lot of copies of the EX that act like yours did....and that's frustrating to me....I want to recommend it to everyone, ( I did when I first got it, but stopped after you had your problems), explaining that you might just have to send it in to be fixed, once, twice, even 3 times, or send it in for a new one is stupid.....
The 50L is not the answer for everyone, just some, and that is lame....
I'm off to shoot some cherry blossoms, cheers
Edit: In the end, I'm glad you found the 50L to your liking and that it suits your style and even happier that I found the Sigma to suit mine, I know both of us have been searching for a 50mm for quite a while.