Adding to what's been said, I believe the worst situation (in terms of seeing dust on a lens) would be: 1) wide aperture 2) depth of field that (even partiall

Adding to what's been said, I believe the worst situation (in terms of seeing dust on a lens) would be: 1) wide aperture 2) depth of field that (even partially) includes objects on the lens itself In normal situations, these two conditions are somewhat mutually exclusive. That is, a wide aperture decreases depth of field, making it less likely for anything as close as the lens to be in (partial) focus. The reason you may see the effects of a dirty lens more with fisheye or wide-angle lenses is that they often have a very short hyperfocal distance (bringing most everything into focus), so it's much more likely that condition #1 won't negate the effects of #2. These conditions would also be likely to occur in low-light macro photography.