canon 55-250 IS blur edge, anyone?

Hi, I have recently bought a canon 55-250mm IS, after reading all the comments on the internet, especially most people said that it outperform the sigma 70-300 APO.

I was having difficulties to get shots focus properly with the sigma on my 350D body. The canon does it slightly better but it doesn't always got the focus right like my kit lens or the 50mm 1.8. The biggest complain I had with the canon is the edge blur in the picture which is not so bad in the sigma pic, so I am wondering if there is anyone having same problem like mine? Or is my lens faulty?
I have some test on outdoor shooting, here are some:

canon 225mm f9 1/200s
full picture

center crop--quite sharp

edge crop

vertical crop(not 100%)

canon 154mm f8 1/400s
full crop

top crop

center crop--really sharp

sigma 168mm f5.6 1/400s
full crop

center crop--pretty sharp a well

edge crop

some more test at:
http://www.flickr.com/photos/jongks/

I did also notice that the canon @250mm is actually wider than sigma @238mm.
Thanks for viewing
KiamSoon

I think you may have a decentered element or something. This does not look normal. You can tell you focused right because the bottom of the tree in the first shot is very sharp, but the top is blurry. At F9, we can't call that a focus error. I'd return it and try another.

I also don't think the Canon lens really outperforms the Sigma for sharpness or AF, it just has IS.

what an insightful comment jonrobertp!

all the shoots are hand held. The edge blur normally happen when I focus to further object, within 20 feet is quite ok. And its worst at tele end.

Ya I notice that as well, unless I am having a bad copy of canon. But I like the canon color and contrast a bit more. Another thing is the sigma is brighter at the same aperture and speed, maybe 1/3-1/2 stop.

It does improve a little when stop down but the edge blur still exist. Both left and right(top and bottom) are blur but the right side is more obvious.
Thanks for your suggestion anyway, I will try it again tomorrow.

Thanks Maarensv, at least I still have hope for the lens after reading your experience, actually I have a lot of miss focus shots, those pictures that I post are some of the better one with this lens. I did actually send to canon for check up once but they didn't find out any problem, maybe it was near christmas and they rush it out.

thien nguyen wrote:

You were shooting at 225mm which is quite a large focal length.
This will give you shallow DOF even at f9.

According to the DOF calculator, on a crop body, say, at 20m away,
the DOF is less than 3 metres and only about 1.6m behind the focus
plane.

So you are implying that the tree is leaning? The top is more than 1.6m farther back than the front? I find that very unlikely.

I did try to shoot a flat roof and its seems ok even at 250mm with minor sharpness falloff at the edge. But I also got quite a lot of shots with the edge blur at wider angle, like the second sample that I have post the roof is blurer on the canon one, even the canon is shot with 154mm f8 and the sigma is shot at 168mm f5.6. I also notice that the right side(top) is more blur than the left side(bottom).

These is another comparison:

canon 84mm f10
center

top

full shot

sigma 86mm f8
center

top

full shot

This picture from sigma is sharp from center to any border even at f8

That seems to be quite sharp. I got a few sharp picture just like yours but most of the others have the blur edge problem, I did try to shoot a flat plane and it seems ok.

BTW I am using 350D which seems to be the problematic camera for this lens according to photozone. But I have read that many 350D users sell thier sigma for the canon and they are happy for it. Ya, I think I should send it back to canon.

Regards
Kiamsoon