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:

http://www.pbase.com/jgrass/focus

Got the test chart from Francis Poon (www.khdotcom.net). 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.

-Joe

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
lenses.

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