I'm trying to do some AFMA on my lenses and so have downloaded FoCal for OS X. When I run this, I have to use manual mode which involves taking a series of pictures (3 sets of 3 from -5, 0 and +5). When I get the tool to analyse the files it predicts AFMA at -534 on my 35L on a 5D Mark iii. Would this indicate a bad copy of this lens? It doesn't have a filter on it.