I have been noticing more and more recently that my D300s seems to be slightly off on its exposure. I shoot completely in manual and if I am going to be shooting in drastic light changes then I switch to Aperture mode. But I notice that when I put the the exposture center on the exposure meter then the photo tends to be on the overexposed side. Am I missing something? I have to typically shoot anywhere from 1/2 - 1 stop underexposed to get the proper exposure. It has done this since I got it a year ago. Also with me wearing glasses is there a technique that I can use to adjust my viewfinder so I can properly manual focus and get off the autofocus feature because more times than not the photo is a bit soft and I would like to get that corrected and feel only way would be is if I do the focus myself. But what looks sharp to me in viewfinder is not sharp when I ultimately take the photo. Is there a trick to this? is there a foolproof test that I could do to correct this issue?