Adjustment Brush: Flow and Feather

Question

Not so much a question, as an observation. Maybe it will help somebody.
I'm not a big user of the Adjustment Brush. I tend to use it occasionally for applying Clarity, Highlight Recovery, or applying/removing Sharpening.
I'd never much paid attention to the Flow and Density settings before today, and I certainly never really understood the Flow setting. The Feather setting never seemed to work as expected too. So, I just spent 10 minutes with a 50% grey image and a -2-stop brush, getting to the bottom of it all.
Density is the easiest setting to understand: it's like a percentage limit on effect opacity. So 100 means that your brush can deliver 100% of your chosen settings.
Flow was a little tricker to fathom. I expected Flow to control how fast the "paint" comes off the brush. But, no matter how slowly I move the brush, it doesn't come out any thicker. Maybe Flow is the wrong word. I worked out that you had to paint the same spot several times with a low Flow setting to get full Density. It's like Single Pass Density.
Feather is where I came unstuck. Setting any more than 0 give you a two-circle brush cursor. To me, this suggests that the inner circle is solid, the outer circle is clear, and inbetween is a gradient curve. In reality, the brush paints well outside the outer circle (increasing with Feather amount), and isn't solid at the inner circle either. This explains why I've always gone over the edge with a feathered brush, and why it always looks bloody awful when painting an exposure adjustment. Thank goodness the guys added Highlights to the brush settings.

Answer 1

Rob Cole wrote:
To be clear (and I think this is what you were saying too): Flow controls amount of paint per unit of time, regardless of brush movement speed..., for example:
flow = 100 -> you'll get full amount of paint instantly, that amount determined by density.
flow = 0 -> there will be zero paint coming out, so not a useful setting.
flow = 50 -> somewhere in between...
No, that's just it: it's not what I was saying. It is what I expected, but not what I found. Time has nothing to do with it. You can take as long as you like, and no more paint comes off the brush. That was the point I was making, and why I said I thought that "flow" was the wrong word. To me, flow is time-related (volume per second).
'Flow' seems to work by rationing the amount of paint in each stroke. It is only built up by extra strokes.