USM (unsharp mask) uses a convolution matrix to apply sharpening. laymens terms: finds edges, applies blur, sharpens local contrast. this is the best form of sharpening for most people. settings of 200-300, .1-.3 pixel, 0 threshold are good starting points for most images.
Sharpen just finds edges and applies a contrast to them. leaving an image unnatural looking in some circumstances.
I use Smart Sharpen, radius of 1.0, and the Lens Blur setting. My sharpening percentage is in the 150% to 175% range. If I have to sharpen at 200% or higher, I usually throw the image away. I have always been happy with a radius of 1.0. I'll have to give a smaller radius a try to see what happens. I got my basic settings from a George Lepp seminar and they've served me well.
Gary
Hey all- first time posting in this forum. Wanted to share a great Photoshop color correction method that works magnificently for aquarium photos. Try this and see if it works for you:
With your image open create a duplicate layer then go to Filter>Blur>Average then invert the color by pressing Control/I. Now go to the Layer palette and double click on that duplicate layer (default name is Background copy). In the Blend Mode dropdown box select Color and use the Opacity slider to make that photo snap. It's working so well for me... here I am posting it
The result is amazing. I've been practicing photocorrection for several years but I didn't succeed in it like you did. I also found an interesting article here about underwater photography tips. I'm gonna try these tips during my next photo shoot. I believe, that the perfect result is only 20 percent of editing and 80 percent of good preparation.