Canon EF 50mm f / 1.2L USM EF50mm F1.2L USM Instruction Manual - Page 6

2. Setting the Focus Mode 3. Infinity Compensation Mark Infinity compensation mark Distance index To shoot in autofocus (AF) mode, set the focus mode switch to AF. To use only manual focusing (MF), set the focus mode switch to MF, and focus by turning the focusing ring. The focusing ring always works, regardless of the focus mode. To compensate for shifting of the infinity focus point that results from changes in temperature. The infinity position at normal temperature is the point at which the vertical line of the L mark is aligned with the distance indicator on the distance scale. After autofocusing in ONE SHOT AF mode, focus manually by pressing the shutter button halfway and turning the focusing ring. (Full-time manual focus) For accurate manual focusing on subjects at infinity distance, look through the viewfinder while rotating the focusing ring. ENG-5