Dud copy of 17-40mm F4L??

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):

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The key is having plenty of light; that's the only real way to be able to trust results. Your shutt spds are very slow. If you get these kinds of results outdoors with faster shutt spds, your 17-40 is a dud. There is no way the kit lens can hang with the L at f4.

The 17-40mm doesn't compare well here.
Have you done a test where you can use a faster shutter speed? I assume you used a tripod??
If you feel confident that you've done a solid series of tests, I'd say you need to get an exchange because that lens is ordinarily an excellent performer. I'm always amazed with the photo quality when I use it.

Good Luck

Thanks for the feedback guys, I did think the low-light conditions were not ideal, but I guess my logic was, if the kit lens can perform in these conditions, why should a pro lens struggle?

I was locked off on a tripod for the tests.

It looks like it's a focus issue. I repeated the tests, tweaking the focus manually and I managed to get this result (a lot closer to the kit lens):

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One things for sure--you got a pretty darn good copy of the kit lens!When I was doing sharpness tests the kit lens often compared well with my L lenses, in some cases outperforming them. It's just when I go out and really shoot with it that the differnces show. The kit lens will be soft on one side of the frame, or it will misfocus more often and the contrast in the image is lacking.

Your 17-40 actually looks very good when you focus manually. They can be a tad soft at f/4 particularly in the corners. I got mine for landscapes so that's not a big concern for me--it does a wonderful job. Test shots are OK to root out obvious problems, but I find I don't feel good about a lens until I take the kind of pictures for which I bought it.

You should expect it to focus better than what you showed though. It's not a very contolled test, but focus tests are notoriously hard to control anyway. I would just shoot a variety of objects at f/4 with good light and if you can consistently focus better manually I'd get it fixed --should be an easy one for Canon.

I found the same at 17/18mm in the center,
BUT look at the edges and corners, the L should put the kit to rest...

The kit should be much softer on the edges than the center, where as the L is the same edge to edge.

Also be sure to manual focus when you test.

err, try comparing the same shutter speed, same Fstop at nothing slower then 1/125th,

Just a thought - the kit lens is a little faster wide open, (f/3.5 vs. f/4) and of course the aperature doesn't set until you take the pictures (so even if you have the camera set for f/4 on both lenses, the kit lens would focus at f/3.5 and then snap down to f/4).

Well kinda boring this evening after cleaning up the Kitchen so I did a test with 17-40L @ 40mm. These are shot in RAW + Converted with Raw Shooter Premium to TIFF + saved as a JPEG via PSE2. No processing straight from the camera. They were took at 1/10s f/4.0 at ISO 400 to get the shutter up a little under the available incandescent lighting and of course resized for the web:

and don't make fun of the book selection

Original Image with Center Focus on the W

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That manually focussed shot is much,MUCH better,and in the ballpark of what it should be doing
You say it might be the bad light that makes it missfocus? I hope it isn't giving you bad focus in normal use.

Thanks for the further thoughts everyone!

Bluedog_XT, your test image sure is razor sharp compared to either of mine! Perhaps the lighting I'm using just doesn't agree with the AF now that I've narrowed it down to a focus problem. I'm definitely going to try some daytime stuff at higher shutter speeds (unfortunately I'll probably need to wait until the weekend thanks to work and the short winter days!) and re-evaluate the situation then. I'll also make sure I keep the shooting parameters identical for both lenses.

You wanna use a shutter release too or a least the self timer. I didn't use the mirror lock up option. Good lighting and the faster shutter should make a difference.

According to Canon's MTF data there is not an enormous difference between the two lenses wide open, particularly within a 10mm image radius, the kit lens falls off fast after that.

Also you don't say what focal length you are working at, the 17-40 MTF pulls away a bit more at the long end. Also are these centre, edge or corner crops. Check the edge and corner and check stopped down at f8.

Hey gcams, have you have a chance to shoot any more with this lens? I ask because mine arrived yesterday and so far I am very, very disappointed. I've take about 300 shots and each time I upload a batch to the PC to get a look, the pit in my stomach grows a little bit larger. Everything I've shot with this lens appears soft and underexposed. I'm working long hours for the next couple days and won't be able to do any serious test shots but my first impression is making me very sad.

@ vixeh: are you shooting in RAW?