Lucky imaging: high angular resolution imaging in the visible from the ground

We use a Lucky Imaging system to obtain I-band images with much improved angular resolution on a 2.5 m telescope. We present results from a 10-night assessment campaign on the 2.56 m Nordic Optical Telescope and quantify the performance of our system in seeings better than 1.0''. In good seeing we have acquired near diffraction-limited images; in poorer seeing the angular resolution has been routinely improved by factors of 2.5–4. The system can use guide stars as faint as $I=16$ with full performance and its useful field of view is consistently larger than 40'' diameter. The technique shows promise for a number of science programmes, both galactic (e.g. binary candidates, brown dwarfs, globular cluster cores) and extragalactic (e.g. quasar host galaxies, damped Lyman-α absorbers).