Originally posted by Wheatfield Lenses have f-stops of 16 or 22.
Going to f/22 isn't a bad idea for this sort of image.
Diffraction is an effect, not a wall.
Ah, but sometimes it's an unwanted effect. One quality of waterfall photos is the juxtaposition of the hard and the soft, the sharp and the misty -- contradictory images in one. Diffraction diminishes that contradiction, softens the entire scene. Of course, stopping down all the way doesn't hurt if the picture is for a postcard.
Originally posted by Naturenut What lens do you think works best? I only have my K20D kit lens (18-55) and a Tamron 70-300mm (I shot with my Tamron, no filter, no tripod...I was in a hurry. lol)
If you want the effect of a misty ghostly splash against sharp surroundings, you'll probably want optimal DOF. That would indicate using the 18-55, fairly wide, with aperture a couple stops from the smallest to avoid diffraction. But being wide also requires being close. At 24mm your smallest aperture is f/27; try f/19. At 35mm, the limit is f/32, so try f/22. Way out at 50mm, the limit is f/38, so try f/27. Or maybe one stop wider.
Or better yet, take some test shots at home of subjects with some fine detail -- the brick wall or a filled bookcase are always popular. On tripod, focused on the target, take shots at all the smaller f-stops, with and without ND filters. See which aperture is sharpest, and if the filter degrades detail annoyingly. (I'll bet it won't, unless it's cruddy glass.) You could also shoot some DOF tests -- the camera-on-a-fence trick works. At the sharpest aperture, find the hyperfocal point that keeps a distance in sharp focus.
Review your waterfall scene. How wide is it? What focal length grabs enough of it? Estimate the distance from your shooting point to the farthest place you want to be sharp. Unfortunately the 18-55 doesn't have a DOF scale, and I don't trust online DOF calculators. So think of your DOF test and focus accordingly. If 24mm covers the scene and you find f/16 the sharpest, hyperfocus to about 10 feet, and you'll be good from at least 4 feet to infinity. If you use 35mm and f/19, a 10 foot hyperfocus is good from 5 feet on out. At 50mm and f/22, 15 foot hyperfocus takes you from 8 feet to forever. I'm allowing a bit of margin there.
You're fortunate to have a scene you can return to and try various tricks. Some people spend years shooting the same tree. None of my trees are that interesting, so I don't do that.