Comparison of imaging techniques

The Lucky Exposures method is expected to have the highest sky coverage of all the natural guide star techniques discussed here, utilising fainter reference stars and providing an isoplanatic patch at least as large as the shift-and-add method. The method is also much cheaper and simpler to implement at observatories than adaptive optics systems.

The sensitivity of the Lucky Exposures method to faint objects is likely to be reduced due to the rejection of a significant fraction of the observational data. However, it is worth noting that for R-band ($600$--$800nm$ wavelength) and I-band ($800$--$1000nm$ wavelength) observations, scattered light from the bright reference stars required for high order adaptive optics correction may also limit the sensitivity to faint objects. At these wavelengths the higher limiting magnitude for Lucky Exposures and a potential increase in the isoplanatic patch size are likely to give sky coverage at least one hundredfold greater than that of adaptive optics at the same wavelength. At longer wavelengths the sky coverage will saturate at close to $100\%$, and the relative benefit over adaptive optics will be smaller.