= Largest contiguous Fresnel aperture
{title2=$w_*\simeq1.20938$}
The largest radius of the normalized <Cornu spiral> occurs on its first outer turn at $w_*\simeq1.20938$, where $\operatorname{Re}[F(w)^*F'(w)]=0$. Oddness makes the chord from $F(-w_*)$ to $F(w_*)$ attain twice that radius, while the triangle inequality bounds every other chord by the same <length>. The interval is therefore the strongest freely selectable connected aperture at that observation point, with normalized point power about1.80142. Signed physical limits follow from $x=w\sqrt{\lambda z/2}$. Existing openings can constrain this optimization.
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