Quickly change a tool’s Opacity setting while painting without having to go to the Options bar each time
When using a tool that involves an Opacity, Exposure, or Strength setting, the quick way to alter this is by using the numbers of your keyboard.
The keys 1-9 change the setting in the Options bar to 10% and up to 90%, whereas 0 relates to 100%.
By pressing two numbers after quick succession, such as 8 followed by 2, you can end up with 82% for a slight increase.
To edit a layer’s Opacity setting and not a tool’s, press V to quick select the Move tool and then use the number keys.