The side focus does the same job as a adjustable objective and the bell of other scopes. when you change the shot from say 25-100yrds the picture will go out of focus and be hard to see, you need to turn the side focus to the aproximent distance and if set right you can look through the scope and place the cross hairs on a set spot. Then move your head so the crosshairs move around in the site picture, the crosshairs should stay on the target spot. If it moves it is set wrong. You will mostly see this at under 200yrds and mainly under 100yrds
