Nikon Epiphot 300 Manual page 29

(12) Stop down the aperture diaphragm to minimum.
The diaphragm image then become visible on the
objective's exit pupil. Rotate the centering tools to
center the aperture diaphragm until the aperture
diaphragm image and the exit pupil are concentric.
I
Objecti ve's exit
pu pi l
Aperture
-0
::a
diaphragm image
m
�
::a
�
0
z
22