Canon EF 50mm f / 1.2L USM EF50mm F1.2L USM Instruction Manual - Page 7

4. Infrared Index 5. Depth-of-Field Scale The infrared index corrects the focus setting when using monochrome infrared film. Focus on the subject manually, then adjust the distance setting by moving the focusing ring to the corresponding infrared index mark. Some EOS cameras cannot use infrared film. See the instructions for your EOS camera. The depth of field is the distance in front of and behind the plane of focus on the subject that appears sharp. The depth of field is indicated by the area between the depth-of-field scale lines below the distance scale. Numbers in the scale are in F values, and for example, if the shooting distance is 3m and the aperture is f/11, the sharp area will extend from about 2m to 5m. ¡The infrared index position is based on a wavelength of 800 nm. ¡Be sure to observe the manufacturer's instructions when using infrared film. ¡Use a red filter also when you take the picture. The depth-of-field scale is an approximate indicator. ENG-6