Canon EF 180mm f3.5L Macro USM - Manual (Page 7)

ENG-6
6. Depth-of-Field Scale
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.
The number on the scale is the F value.
The depth-of-field scale is an approximate
indicator.
5. Infinity Compensation
Mark
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.
Infinity compensation mark
Distance index
COP
Y