Dud copy of 17-40mm F4L??

Hi All,

I just thought I'd let you know what came of my introduction to L lens disappointment. I returned my suspect 17-40mm F4L lens and the supplier confirmed the lens was faulty through their own testing. They dispatched a replacement and now I'm a happy camper!

One thing that was immediately obvious with the replacement copy was the focus ring was *very* smooth compared with my first copy (probably not relevant, but made the lens feel nicer!).

Putting that aside though, my kit lens no longer shines against my new 17-40mm L copy. At 17/18mm F4, the L lens is now definitely sharper than the kit lens (the way it should be!). Looking back at the images I was getting out my first 17-40mm F4L copy, it is like chalk and cheese!

My faith in Canon L glass has been restored and I'm looking forward to trying my new F4L copy "in the real world".

Thanks to everyone who inputted to this thread and especially those who encouraged me to return the lens and get another copy! I'm very glad I did!

Please post a pic or two from the copy...

Ok, here's the results of one of the 6 or 7 tests I've run now and the results are consistent. Tests are the usual tripod setup with self timer and mirror lockup.

Kit Lens @ 18mm/F4:

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That does seem better indeed.

gcams wrote:
I've been doing some testing in the last hour, comparing my 18-55mm Kit lens with my 17-40mm F4L and my gut is sinking more and more every test I do. I keep getting the same results, with my el-cheapo kit lens producing consisently sharper images than my £500+ L lens, especially noticeable at the wide end.

Here's the damning evidence so far:

F4L (100% Crop):

Hosted photo: posted by gcams in
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forum: Canon Lenses

Then my 18-55mm Kit lens

Hosted photo: posted by gcams in
./showthread.php?p=946​420&i=i119255422
forum: Canon Lenses

Both shots were taken with mirror lock up on, the F4L shot was taken at 1/8th, the kit lens at 1/4, both F4, full wide on both lenses. (EDIT: Meant to add I had the focus point locked to the centre focus point on my 350D in both case). I took three shots on each lens and the results were the same each time.

I did 3 other seperate tests with 3 different subject matters and all 3 produced similar results, the kit lens blows the 17-40mm L out the water every time. Am I missing something here or have I got a dud??

Thanks All!

DUD -- OR its is back or front focussing
Try manually focussing OR focus on a BIG ruler at an angle and see if it's in focus where you expected it to be