On second thought: With obstructed telescopes and mirror lenses you can have bad diffraction effects due to the secondary mirror and its holder but in most normal camera lenses it is not an issue. I suppose if you had reflective aperture blades you could have similar problems with them but I've never heard of anything like that. Perhaps circular aperture blades could help reduce those sorts of diffraction effects like diffraction spikes but I've never seen them outside of astronomy where there are point source lights. Perhaps in scenes with lots of specular highlights? Still sounds like stuff you won't encounter often.