Shocking insight: AF is not a closed feedback loop!

Started Jul 18, 2003 | Discussions thread
Joe Grass New Member • Posts: 19
I sent in 10D & 3 lenses (pics)

My 35mm F2 and 17-40mm F4 focus PERFECTLY, but when I later tried THREE copies of a 70-200mm F4, they all back focused.

So I kept one 70-200 F4, and sent it with all my lenses and 10D to Irvine last week.

I only noticed the problem on the 70-200 F4 when I got blurry photos, and started noticing the background was in focus. Then I tried shooting some focus charts, and there it was, a very consistent back focus problem.

Here are some test chart photos:

Got the test chart from Francis Poon ( Thanks Francis!

I'm hoping Canon can adjust this all out, without messing the lenses that already focus correctly. I think I will also rent a different body (1DS? Elan 7?) and check out my lenses when they come back. I'm hoping they don't adjust the 70-200 F4 to match my 10D, and nothing else!

Thanks VERY much Mishkin for your very informative post(s), and I'll let you know how it all turns out for me.


Mishkin2 wrote:

it's just very exhausting that I went through FIVE 24-70's and they
all can't consistently shoot sharp pictures at 24mm f/2.8 - with
camera which doesn't have any significant issues with my other 4

I understand now that I need to send my camera and lenses to Canon,
but I'm afraid to get screwed up and then to beg for weeks for
special attention from Canon.

-- hide signature --
Post (hide subjects) Posted by
(unknown member)
Keyboard shortcuts:
FForum PPrevious NNext WNext unread UUpvote SSubscribe RReply QQuote BBookmark MMy threads
Color scheme? Blue / Yellow