Double Negative wrote in post #2322357
True, but typically the rounder the aperture (as is the case with 8-bladed apertures vs. 5-bladed ones and the new "circular aperture" feature in some new L lenses) the better the bokeh. I'd rather see slightly worse bokeh from an 8-bladed aperture than slightly better from a 5-bladed aperture... Pentagons all over your background aren't "cool."
If the shapes are faded, they aren't that easy to see. I can see the aperture shape in this image:
But the shape is not objectionable at all. On this one, the aperture is round, but the bokeh is objectionable:
For lenses used wide open, it doesn't matter because the aperture will be round.
My point is that many folks will say something like, "this lens, with its 7-blade diaphragm, has excellent bokeh." That statement does not follow. The lens that made the second image above has 10 or 12 blades in the diaphragm, but the bokeh still sucks. It has to be designed as a package.
Where you see the aperture shape is when you have out-of-focus specular highlights using a smaller aperture, in the 5.6-8 range, perhaps. At smaller apertures, the points on the diaphragm are more apparent because of the geometry of the mechanism. The lenses I own with good bokeh have never, however, made me wish for more aperture blades.
Rick "thinking most lens diaphragms approximate round pretty well at wide apertures" Denney