Also because of things like angle of incidence?
The purely round lens will generally have nice round (or at least cats-eye) bokeh across the frame with an edge that degrades softly as a result of aberration, so beams of light from different angles tend to blur into each other.
As soon as you get aperture blades, you lose that soft edge, get contrast but also a lot of competing shape influences at different angles. They will tend towards more rounded shapes as you stop down more.
And that is putting aside that some aperture shapes are just really insane when they are nearly wide open, right? (Konica 40mm f/1.8 AR I am looking at you with your shuriken bokeh)
> I haven't seen a diagram of how the aperture in this new iPhone is designed yet. There's a lot of different ways to do it, with lots of odd shape possibilities.
Not a diagram but one closeup photo:
https://petapixel.com/2026/09/19/apple-explains-why-the-ipho...
and an animation:
https://petapixel.com/2026/09/09/iphone-18-pro-has-apples-fa...
Six blades with a slightly rounded hook in them by the look of it. Very noticeable sun stars at f/1.8, nice looking results at f/2.8.
Absolutely insane mechanical challenge and assembly challenge.