I aquired a used 500 series hassy with a 80 lens. I have been using it quit regualry and have noticed a small loss of sharpness. Now I have used the hyper foucus scale and the distances in the photography meet the range. Does any one have any tips for achieve a pristine foucus? Can this lens be off calibration or is there a way to set the calibration for foucus. Also would a prism help to achieve finer foucus. Any useful hints for fine foucsuing would be greatly appreciated.