I learned this while talking to a fellow photographer last week. It seems quite interesting and honestly didn't know you could go about it with this filter.
I usually apply a very light unsharp mask to get a little more focus on most images.
Amount: 40 to 100 (the higher value for files created with a digital camera the lower for scans of a negative)
With the same tool you can create a similar effect (makes me think of acutance). It actually creates a small amount of contrast in the edges (where shadows meet highlights)
I tried to show it in a before/after image but it is hardly noticeable. Many of you probably know about this already, I didn't