75
Release the lens holder ring by rotating clockwise
and lower the lens holder midway. Fasten the holder
at the position by rotating the ring counter-clockwise.
Place a piece of tape on the beam outlet.
Refer to the steps of "Third Reflecting Mirror" and
readjust the screws behind the third mirror so the dot
is located at the center of the circle.
Release and remove the whole lens holder. Place
a piece of tape on the location shown in the picture
below. Apply pressure to make a circular mark on the
tape.