The IS system on the EF-S 17-55mm f/2.8 is tripod-sensing, so unlike some older lenses (e.g. 300mm f/4L IS), it turns itself off when vibration falls below a certain level (which happens on a solid tripod). So, turning off IS is probably not the answer.


Shutter release on the 7D is very well-damped, so that shouldn't cause significant vibration - not to the degree of unsharpness you're seeing in the pic you posted.