The Power of Gray - The Photoshop: Professional Retouching and Compositing Tips, Tricks, and Techniques - page 104

Figure 2.28
7. A common mistake with dodging and burning is having both the brightened and
darkened areas very defined and not blending into each other. But because we are
on a 50% gray layer we can do something about this. Use the Lasso tool to select
an area of dodging and burning that you want to blend together ( Figure 2.29 ) , and
then go to Filter > Blur > Gaussian Blur. Now increase Radius to whatever amount
you think softens the blend between the dodging and burning the best ( Figure
2.30 ) , and click OK.