4. Infinity Compensation Mark 5. Hood
Infinity compensation mark
Distance index 
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.
For accurate manual focusing on subjects at infinity distance, look through the viewfinder while rotating the focusing ring.
The dedicated Lens Hood
To attach the hood, loosen the hood locking knob by turning it counterclockwise. Fit the hood onto the lens hood mount, and tighten the locking knob to fix it in place. Use the same procedure, in reverse, to remove the hood.