Problems with edge clarity of photos

[Geoff Port]

Hey all,
I've been noticing that some of my photos are not as sharp at the edges as others. I have included a shot of our town library I took yesterday morning. While tickling it up I noted that the left background of the building was not sharply focused and I couldn't tweek to make it any better.
I would have thought that at f16 everything from front to back left to right should be sharp. There is also a degree of offset/ out of register, in that area.ie; a partial ghost of posts.
The shot was taken on tripod and with an IR remote with AF and Stabilization both engaged.
This only seems to appear with photos that are busy across the entire shot. Landscapes with out large amounts of subject matter at the edges don't seem to be effected but maybe thats just because theres nothing in shot to show it up.
Q1: Is this problem my because of something I am doing wrong?
Q2: Could it be the lens (Canon 18-55mm f3.5-5.6 IS II) a kit lens that came with the camera and remarkable cheap.

http://i1068.photobucket.com/albums/u455/GeeKayPee/KeatingsWeirLibrary016.jpg
File Size: 292 kb - 1023 x 682
Camera Make: Canon
Camera Model: Canon EOS 60D
Date/Time: 2012:08:25 08:38:30
Resolution: 1023 x 682
Flash Used: No
Focal Length: 18.0mm (35mm equivalent: 28mm...
CCD Width: 22.99mm
Exposure Time: 0.017 s (1/60)
Aperture: f/16.0
ISO Equiv.: 100
Whitebalance: Manual
Metering Mode: center weight
Exposure: Manual
Exposure Mode: Manual

[ricktas]

Lenses are never as sharp at the edge as they are in the centre, its just physics of lens design. Some lenses are worse than others.

[arthurking83]

It's 99.9% most likely to be caused by the lens!

But just to counter what Rick said .. I'm, sure I've seen a test on a lens that indicated that it was sharper at the edges than it was in the centre!! :confused:

LOL!(if I find the test page, I'll post a link to it here.

But if you want nice clean shots all across the frame at wide angle focal lengths, you may need to do some research, or just spend up big on the established products!

Sigma 10-20mm f/4-5.6 shot at about f/11 or smaller should provide some assistance.
It's displays some good sharpness IQ quite deep into the corners, but not right at the corners of the frame.

It also looks as tho with that fuzzier left hand side of the image you may have a problem with your kit lens too.(not an uncommon situation).
If it's fuzzier on one side compared to the other, then the lens has a decentering defect, where the lens elements inside the lens barrel have moved slightly with respect to each other.
This could be from the factory(and should be replaced under warranty immediately) .. otherwise, as in my case now .. the lens may have taken a few too many hard knocks.

My personal recommendation (to this current situation of yours) .. if you can spare about $400(odd) .. have a search for a Tamron 17-50 f/2.8 to replace this one lens as your 'standard kit lens'.
Another lens that's quite high on value for money!

[nhoj]

You might try turning stabilisation off when using it on a tripod.

[swifty]

I agree with what everyone has said so far.

With respect to your lens, I assume this is the one:
http://www.lenstip.com/304.4-Lens_review-Canon_EF-S_18-55_mm_f_3.5-5.6_IS_II_Image_resolution.html

Look at the graph of the resolution, particularly the edge. Firstly the edge is lower than the centre and secondly for your lens, both centre and edge resolution are in decline by f8 so there's diminishing returns as you stop down, not to mention the negative impact of diffraction.
DOF is certainly not a problem at 28mm equivalent and at the distance in your shot. A shot at f5.6-f8 would have yielded better results.
Also as mentioned, leave IS off on a stable tripod. Ironically you may have had better results at 1/60 second, 28mm, IS on hand-held compared to tripod mount.