Coupling efficiency as a function of calculated RMS wavefront error at 1550 nm. The ExAO, AO and seeing regimes are highlighted for convenience. The coupling efficiency limit due to spiders and apodisation optics is highlighted in red, while the limit without apodisation is in blue. The dashed black line is Marechal’s approximation to the Strehl based on the wavefront error calculated from Eq. (A.1). A clear correlation between the Strehl and coupling is visible.