The 50 1.8 is probably the cheapest lens you can buy these days. Are these fairly new purchases or are they a few years old. I wonder if the focusing machanisms are just worn and are no longer in sync? The review of the lens on this site was not to favourable but it does state:


The Canon EF 50mm f/1.8 II Lens' strongest quality is its sharpness. Sharpness performance wide open (f/1.8) is decent, but the Canon 50 f/1.8 is very sharp at f/2.8 and beyond. It is slightly sharper than even then Canon EF 24-70mm f/2.8 L USM Lens.


You would think you should be getting decent shots. Just not sure why you would use a lens of that quality on a 7D or 5D [:P]


MattG