Bushnell Stableview 18-1035 Quick Reference Manual page 9

HOW TO ADJUST AND FOCUS
Eyepiece
Rotate the rubber eyecups up or down to adjust the height. If you wear
glasses or sunglasses when using the binoculars, set the eyepcups at their
lowest positions.
Interpupillary adjustment
Use both eyes to look into the eyepieces and adjust the interpupillary
distance to match the distance between your two eyes until you see just
one perfectly circular image.
Diopter adjustment
You should perform the diopter correction before first usage, as the vision
of your two eyes might be different.
Close your right eye and use only your left eye as you adjust the focus
control knob.
Once you get a sharp image, close your left eye and open your right eye.
Turn the right diopter adjustment ring to focus for the right eye. (Do
NOT use the focus control knob.)
Now look through the binoculars with both eyes and make sure the
diopter adjustment is perfect. Only the focus control knob should be
needed for later focusing.
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