one bad thing about photoshop, its greyscale mode is 8bit, and as such only works up to 256 shades of grey. Very odd actually, especially when compared to a program such as zbrush, which isn't photo oriented at all, but its greyscale mode works at 24bit i believe, something like 65000 shades of grey. of course, maybe all this changed in photoshop 7, i dunno.