Imaging Atmospheric Cherenkov Telescopes (IACTs) are instruments for the indirect detection of very high energy cosmic and gamma rays, since they are essentially very large light buckets used to gather the optical Cherenkov photons generated within extensive air showers.
Whilst the imaging quality of their reflective surfaces may be crude it should not be forgotten that they are in actuality amongst the largest optical telescopes ever constructed -- with sensitive camera equipment ideal for application to high time resolution optical astronomical research from scales of seconds down to nanoseconds.
Recent advances in instrumentation have resulted in the VERITAS IACTs making sub-milliarcsecond resolution observations through the revived technique of intensity interferometry and obtaining the smallest optical angular resolution measurements to date in direct measurements of stellar diameters at the ~100 micro-arcsecond scale from observations of asteroid occultations of stars.
There are many further diverse non-gamma-ray applications that these types of telescopes are starting to contribute to: from the simultaneous search for optical counterparts to Fast Radio Bursts, to the search for extraterrestrial intelligence.
This increased range of utility for these form of telescope expands their potential remit from facilities for specialised purposes to observatories for a wider scientific community in prime locations around the world.