Had a customer ask me about zip focus on a
binocular, specifically, what is zip focus? Well, it's a version of Bushnell's Insta-focus, as seen on this model of
Bushnell Powerview 10x50. Instead of a conventional center focus wheel, a
zip focus or
Insta-focus binocular uses a pivoting lever, which you depress alternately on one side or the other to focus the binocular. The advantage of a zip focus binocular is that the binocular focuses quicker than a conventional center focus binocular, but the disadvantage, and the reason you only see it these days on cheap binoculars, is that it tends to wear out quickly, compared to a center focus
binocular.