lens - Do rounded edges on aperture blades improve image sharpness, and how?

In the description for the XF lenses for its new X-Pro system, Fujifilm crows:

The [XF lenses] all offer precise control over depth-of-field and deliver excellent out-of-focus bokeh thanks to the design of the molded aperture diaphragm blades. The blades are curved to create a circular image at all aperture settings, while the very edges of each blade are meticulously rounded off rather than simply cut off, which delivers a sharper image. [Emphasis added]

I understand that curved blades — often described as rounded blades — help out-of-focus areas appear more attractive when stopped down, by producing a circular bokeh pattern instead of a polygonal one. But this is bragging about something else: apparently the edges are smooth in the other dimension.

Does this really matter?

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  Will it really improve sharpness? Does it affect diffraction in some way?

  
  


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  What about subjective qualities — might the bokeh be affected in some way?

  
  


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  Is this construction used on other modern, premium primes with rounded aperture blades, or is it unique?

  
  

Answer

The edge of the blade may reflect light. Such internal reflection is certainly to small to produce visible flare but may introduce some kind of blur. Rounding the blades will reduces this parasit reflection.

As these reflection may possibly show-up in the bockeh it may be slightly improved.

Diffraction will be not be directly affected.

I don't know if the effect of rounding the blade is really visible, however it hopfully indicate that ingenieers have also taken care of other optical defects with the same or higher impact.

Otherwise it's just a marketing argument.

Let me elaborate about diffraction: The wave has to pass through the hole between the blades. Using Huygens-Frensel principle (building the next wavefront by tracing circle with same diameter on each point of the previous wavefront) you can see that it the second side of the blade encountered by the light which determine the exiting wavefront. Then the light will propagate until the sensor where one record the typical interference of the diffraction. Therefore only the side of the blade closer to the sensor account for the diffraction. The blade thickness has no impact.