Whether you’re painting or masking with the Brush tool, one thing holds true: You often need to zoom way in for precision pixel control, but then zoom back out to get a big-picture preview. But switching between the Brush and Zoom tools so frequently will disrupt your painting groove. Not to worry. You can swap tools and remain efficient with a simple keyboard combination.
First, you need to enable Scrubby Zoom: Choose the Zoom tool and select Scrubby Zoom on the Tool Options bar. Now, select the Brush tool and get painting. To zoom in while using the Brush tool, press and hold [command][Space Bar] ([Ctrl][Space Bar] in Windows) to temporarily switch to the Zoom tool. Drag to the right to zoom in or to the left to zoom out. Release the keys to resume using the Brush tool.