Zoom With Scroll Wheel

You can use the scroll wheel on your mouse to zoom in or out an image by pressing Alt (Mac: Option), and scrolling the wheel up or down.

You can also press Ctrl K (Mac: Command K) to bring up the Preferences panel, and turn on the “Zoom with Scroll Wheel” check-box, found in the Tools tab (General Tab in CS6 and older). This will allow you to zoom in and out by simply using the scroll wheel, without the need of pressing Alt (or Option).

preferences-scroll-wheel wheel, without the need of pressing Alt (or Option).