I'm using a wacom tablet as my input device and would like to scale my brush up and down interactively without using the [ ] keys like I can in photoshop. When using a touch pad on a MacBook it can be done so the functionality is somewhere in the software, but is there a keyboard shortcut/toggle to do this when using a mouse or stylus ?
I, too, am an Intuous 5 user. And, while the brush scaling can be assigned to the ring, I have a better way (for me) to do on-the-fly scaling of the adjusmtent brush size.
I'm a PC person, and my normal mouse has a scroll wheel on it. (Not sure if this will directly translate to Mac people.) In normal operations the scroll wheel zooms the scale of the brush larger/smaller.
So, when using the pen for adjustment brushes, I "dock" my mouse on a nice thick "washcloth" size microfiber towel (so that the mouse doesn't "move" at all) and use the scroll wheel to make brush size adjustments while my other hand has the pen and is "drawing" the adjustment area. I get very fluid changes in size "while drawing." A good example of where this is helpful would be in using a highlight recovery brush on a highlight section of a tree branch that is getting progressively smaller. Works GREAT.
Give it a try. I find it much more precise than the somewhat fiddly ring control on the I-5 where the tactile touch is less certain, and certainly more fluid than the choppy action one gets using the bracket keys.
Another trick I've found useful is to assign the lower rocker switch on the pen to "precision mode." This helps with not only very precise use of the adjustment brush, but when using the pen to adjust sliders I get "single digit" changes with "pen on slider" when I press the lower rocker.