Image quality

Using bright reference stars, the Lucky Exposures method can provide I-band images of exceptional quality from a telescope of $2.56$ $m$ diameter under good seeing conditions. The measured Strehl ratios are consistent with those predicted by numerical simulations. The images of close binaries showed very good agreement between the stars, while there was evidence for some anisoplanatism in wider binaries. Spatial autocorrelations of $\zeta$ Boötis indicate that the re-centring of short exposure images works most effectively when the short exposure Strehl ratios are high. The image resolution obtained using the Lucky Exposures method decreases gradually when the fraction of exposures is increased.

Observations of M13 indicate that high precision relative astrometry should be possible in crowded fields given good charge transfer efficiency and a suitable understanding of the plate scale and relevant aberrations.