opacity of anywhere between 4-8%. I like to keep opacity low so I can just lightly layer in the effect with each brush stroke with a lot of control as to how much I am adding. Next, I paint anywhere I want darker in black and anywhere I want lighter in white. Remember the key is to keep in mind how you want the image to be visualized by the viewer and plan your brush strokes accordingly. I do many separate brush strokes in each area until I start seeing the effect set-in. Now, I know some die hard Photoshop enthusiasts are saying why not do separate layers for the dark and light areas so each is independent of the other? That certainly could be done, but I try to keep my number of layers to a minimum so I don't bog down my system and I find that if I have gone too dark somewhere then I just paint over it again with white to lighten it and vice versa. If you over do it a bit, you can always decrease the opacity of the layer itself. Now for that little extra something just to make it all transition smoothly. I like to go to Filter-&gt;Blur-&gt;Gaussian blur and add about anywhere from a 10-30 pixel radius of Gaussian blur to the effect to get a smoother and more subtle look. This is my secret sauce so to speak and I find it does wonders especially when applying this effect