The name of Self focusing binoculars, or as they are also sometimes called Auto Focus Binoculars is somewhat misleading, as they should really go by the names of fixed focus, focus free binoculars, or at least always in focus binoculars. This is because they don't auto or self focus at all, they are basically permanent focus binoculars that have no focusing mechanism and have been designed with a wide, but fixed depth of field from a reasonably close distance (usually around 40ft) to infinity. (They have a large hyperfocal distance.)
What this means is that everything from usually about 40 feet to infinity will remain in focus once you have set them to your eyesight and so you do not have to make any additional adjustments at all.
So how do auto focus binoculars work?
Well to achieve this the binoculars have been set in the factory to focus on a distant object and their optics use your eyes natural ability to focus. To set a fixed focus binocular for your eyesight, you adjust the diopter of each eyepiece to your vision and then from then on they require no further adjustments.
Why all the confusion with the names?
The confusion in the name and the tag of Self focusing binoculars has probably been brought about by clever marketing strategies from the major manufacturers of this type of binocular trying to make them sound more sophisticated than they actually are. What ever you wish to call them, Fixed focus, or always in focus binoculars have been around for over a few decades now they have their uses and there are some excellent quality binoculars of this type out there.
Always in Focus Binoculars sound great, but are considered to be a compromise in design, suited for convenience, but not well suited for work that falls outside their designed range or uses.
Automatic Focusing Binoculars were initially made popular by the brand "Jason" which was established in 1947 in Kansas City. The Jason brand made a group of self-focusing binoculars that became very popular in the 1970's and early 80's. The Jason brand of binoculars was then bought by Bushnell who have now re-branded them as their PermaFocus line of auto focus binoculars. As far as I know, Jason Binoculars are no longer in production.
Video Demonstrating the Bushnell 8x25 PermaFocus Focus Free Compact Binoculars
Below are a few selected Auto Focus Binoculars (Fixed Focus)
View >> All Auto Focus Binoculars