Damien Parker, a friend of mine from Australia, asked me about faking Neutral Density Filters in post processing. At the time I was kind of stumped, but gave him a quick answer, “Try using masks and Gaussian Blur in PS”. However, his question planted the seed in my brain, and I was hooked on finding a better response.
After fiddling with the image from Concert #13 the Clarity slider in Adobe Camera Raw, I noticed the water started to blur in an unusual way. It started to blur, but keep some detail in a fuzzy way while keeping some very nice reflections. It was a very similar effect received from an ND filter.
I put that in the back of my mind until I tried it on a few more images. I kept opening them as smart objects and making history states and jumping through all kinds of hoops until I stumbled upon creating multiple Adjustment Brush points set to effect the clarity only. There it was, the faking of the neutral density filter!