Left side blurry on 24-105mm f/4L IS lens
I have an intermittant problem with this lens. I'm often not entirely happy with the edge sharpness of the lens at the best of times, but occasionally I find that the left side of the frame is extremely blurry. I haven't been able to easily replicate the problem so I'm not sure if it only happens when IS is on, but I suspect it is the cause of it.
Anyone else experienced a similar problem and would you consider this to be a normal occasional 'side effect' of the IS function, or is it faulty?
Here's an example of it.
To be fair, it might be an extreme example of using IS, as I was on the back of a speeding catamaran and it was pretty bumpy. Does the IS 'fail' under conditions like that? And if so, does it typically only affect one side of the lens? It seems to only happen on the left side from my experience...
Any advice appreciated.
PS: I should mention that this is shot on a 5D and I don't think it's simple motion blur - it was shot at 1/320th of a sec at 105mm with IS enabled. The rest of the frame is also fairly sharp, so it seems to be something lens related.