with your binocular perfectly calibrated to your vision. Not only is a lockable diopter helpful, but the extra attention that the manufacturers show to the small details as well as to the needs of the user is a really nice touch and is often an indication of quality, which usually extends through the whole binocular including the optics and build quality. Video Demonstrating How to Calibrate & Focus Binoculars Below is an excellent video created by the guys at Vortex Optics that clearly demonstrates how to correctly calibrate your optics to your vision on binoculars that have the diopter adjustment ring located on one of the barrels as well as ones that have it located on the central focusing wheel: Fixed Focus Binoculars So far we have talked about how to focus and calibrate the most commonly found "center focus" type of binoculars, but what other types of binoculars are there? Fixed/Self Focusing Binoculars If you don't want to have to focus your binoculars when viewing objects at different distances away, you could try using a pair of so called self focusing binoculars also sometimes known as focus free binoculars (they are not really self focusing at all, more of a permanent focus system). Please note that you will still need to calibrate them when you first get them in much the same way as standard center focus binoculars to compensate for the differences in your eyes.