Hi, thanks. No, I alter the opacity by the pressure of the tablet pen. The Wacom Intuos5 has 2048 levels of pen pressure. Basically, in Photoshop, I set the opacity of the brush to Pen Pressure. I explain it a bit more in one of my other tutorials here:
Sorry, just to clarify, with opacity set to pen pressure, if I draw lightly with the pen, the 'paint' in Photoshop is almost 0% opacity and as i press harder, it will go up to 100%... with practice, it becomes very natural. Unlike a mouse which has either on or off, you have to set the opacity manually and becomes quite a cumbersome way to paint.