 Deformable-mirror control radius

With $N$ actuators across diameter $D$, the projected pitch is approximately $D/N$. The Nyquist spatial frequency is $N/(2D)$, so the largest correctable angular speckle displacement along an actuator row is $N\lambda /(2D)$. A square actuator array gives a square ideal spatial-frequency region. See the Bordé–Traub wavefront-control derivation.