Canon EF 600mm f/4L IS III USM EF600mm f/4L IS III USM Instruction Manual - Page 20

11. Infinity Compensation Mark 12. Hood Distance scale Infinity compensation mark The custom lens hood cuts out unwanted light and protects the front of the lens from rain, snow, and dust. Distance index To compensate for shifting of the infinity focus point that results from changes in temperature, there is a margin at the infinity (∞) position. The infinity position at normal temperature is the point at which the vertical line of the distance scale L mark is aligned with the distance index. OO For accurate focusing in MF on subjects at infinity distance, look through the viewfinder or at an enlarged image on the LCD monitor* while turning the focusing ring. * On cameras capable of Live View shooting Lock knob Attaching the Hood Loosen the hood lock knob by turning it counterclockwise. Fit the hood onto the lens's hood mount, and tighten the lock knob to fix it in place securely. To stow the lens, reverse the lens hood and slip it over the lens. ENG-19