This is actually a great program for people who LOVE math!
and learning to use the controllers is going to be a big plus for you- I would suggest running through all 3 basic tutorials listed in this forum...
But, what you want to do is a set of controller 'blocks' that feed into the Brush Parameter for Opacity.
First, in the far right sidebar of the screen, under SHAPE, set your opacity to your favorite Maximum opacity, (for a full swathe, set it at 100%)
Now, open the controller Editor.
Click on the Opacity Brush Parameter
Here you will want to create a chain of controller blocks that feed into each other, the first being pressure on the far left, the second being EASE CUBIC (to smooth out your pressure and give you low pressure control) and then Ease Cubic feeding into the OPACITY brush parameter..
These of course combine with any other brush parameters that are already set, it's a multi-dimensional tool.
I think my response might be way too rudimentary, but, I hope it helps.
I have been using Photoshop for 10 years creating digitally printed wallcovering.
I have an electrical engineering degree with a minor in math.
I am a freelance designer, writer, and developer. matt @ remarkable team dot com