This video from the USA says about itself:
How to get crystal clear focus with your binoculars
5 November 2014
The Cornell Lab of Ornithology in the USA adds:
Migrants are migrating, days are cooling down, and winter birds are getting ready to flock around your feeders. Now’s the time to make sure your binoculars are giving you the best possible view. For some fast tips on setting up your binoculars (including the mysterious “diopter”), and how to find and focus on birds, watch this video.
More Ways to Get the Most From Binoculars: