I copied this from a post a while back (posted by Max Jacoby), hope it helps
"Angénieux Optimo zooms only have 6 straight iris blades (you can see that very well in American Gangster, which is a mix of Optimos and Cooke S4s and it very easy to tell which is shot on what).
Zeiss Superspeeds have 7 iris blades (except for the MK1s, the very first version, which only had 3, giving it the ugliest bokeh ever)
Cooke S4s,have 8 blades which are bend inwards.
Zeiss Master Primes have 9 curved blades, so that even when stopped down, the highlights still look quite round.
Zeiss Ultra Primes have 9 or more straight blades (the longer lenses have more I'm told, but I haven't checked yet which lenses exactly)
Primos have 11 bent iris blades. They have a similar shape to the Cookes, but because there are more, it is less annoying. I think there might be some wider Primos that have 10 blades, but once again I haven't checked it yet.
Zeiss Standards have 6 iris blades
Most modern films are shot on either Cooke S4s, Primos or Zeiss lenses. Since the bokeh of Primos and S4s is very distinctive, one can usually conclude that if it is absent, a Zeiss lens was used"