My old S2 has that zoom control as well as my daughter's S4. I went to one corporate store repair center which said the volume rocker button does not control the zoom. I called Sprint customer service and was told my unit must be defective . The Sprint store checked its phones, not one of the S 5's had the volume/ rocker zoom control, so they said that's the way they're set up and there's no setting to change that .
I then showed them the Sprint on line s5 Manual, namely page 81, which clearly states the volume rocker button DOES control the zoom in both picture taking and video recording . There is also the method of pinching the screen to zoom in and out., but that is difficult , because you're then holding the phone with one hand ,which is not conducive to good picture taking .
So, how do we get the volume rocker button to control the zoom?