Sometimes we need to paint, stamp or dodge and burn using just a portion of the full force of the tool, which means - changing opacity. As well, usually, it means that we have to divert our attention, move the mouse to the tool bar and do a few additional clicks. At least this is the most obvious way. But with a simple shortcut we can pick any 10% step from 0 to 100%. How? Easy, simply press the number 1 through 0. 1 stands for 10% and 0 for 100%.