Back focus explained
✓ Canon introduced the back focus button in 1989 and it has become a standard feature on most Canon cameras.
✓ This article from Canon thoroughly explains back focus
✓ The back focus button physically separates the focus button (switch 1) from the shutter release button (switch 2)
✓ This separation is beneficial when shooting sports as the shutter can be released (switch 2) without having Auto Focus activated (switch 1)
✓ The Essex Back Focus Pistol Grip incorporates back focus functionality in to a ergonomic and easy to use pistol grip