OK, I hope this isn't too stupid a question, but I've searched this forum and other 'net resources to no avail. My apologies if this has been covered elsewhere and I missed it.
I see many references to backfocusing and/or frontfocusing, and while I have a general understanding that these terms mean "out of focus," I would like a more detailed definition and explanation of the cause(s). Does fault typically lie with the camera body, the lens, or both? For example, some posts lead me to understand that an interaction between the camera body and a particular lens can sometimes cause this, but it is not clear to me exactly how and why this happens.
Also, are there any particular tests one should perform to check for this (apart from the obvious one of looking to see whether your pictures are in focus 
)?
