Photoshop Brushes: Flow vs Opacity Part 2

This is a follow up to an article that I did quite some time ago about about the difference between “flow” and “opacity” using Photoshop Brushes.  This has become a very popular article and a reader brought up a point which I thought would be good to address.  If you haven’t read the first article, I suggest you go back and read that one first because this is an addendum to that article.

In the last article I created a brush made up of lots of overlapping circles to show the effects of changing the opacity and flow settings.

A reader then made the following observation:

The effect shown for “opacity 100% and flow 50%” can be achieved with “opacity 50% and flow 100%” if you paint one overlying circle at a time… 🙂

Yes, the reader is correct.  If you set the opacity to 50% and the flow to 100% and make one long brush stroke it will look like the middle sample above.  But, if you make lots of small one-circle-long brush strokes, it will look like the bottom sample.  Why the heck is that happening?

In the example below, I set the opacity to 50% and the flow to 100% and the mode to “Normal.” I then made 8 different brush strokes, which means I touched my stylus to the tablet 8 different times lifting it off the tablet in between (if I was using a mouse, I could have clicked my mouse button 8 separate times)

As you can see I have made notes where each brush stroke starts and stops. The opacity setting only governs the opacity within a single brush stroke.  Which is an important point to keep in mind.  If another brush stoke comes by later and overlaps it, it will change the resulting opacity in the area of the overlap. 
Hope this helps clear up any confusion.