Timing the variable gamma ray emission from mergers, bursts, recurring novas, flaring jets, clocking pulsars, and many more is key to constrain physical models. For good timing on account of high rates, we would ideally collect the abundant low energetic 1GeV gamma rays, for which the universe is still transparent up to high red shifts, in large areas. Satellites collect low energetic gamma rays but only in desk sized areas. Cherenkov telescopes have multi soccer field sized collecting areas but only detect the rare high energetic gamma rays above several 10GeV. We propose a ground-based instrument that detects 1GeV gamma rays in a large area and hence achieves huge gamma ray detection rates: the Cherenkov plenoscope. With an over 100 year old, but apparently still groundbreaking optics, the plenoscope enables for the first time the high-resolution imaging of low energy gamma ray air showers using a huge (71m) mirror. By measuring not only where a photon is absorbed on its camera screen, but also where the same photon is reflected on its mirror, the plenoscope can tolerate deformations and misalignments of its mirror and camera. This reduces the plenoscope's cost compared to a telescope. We will introduce the plenoscope's optics, demonstrate its performance and especially its resilience to deformations and aberrations. We will also compare the plenoscope to related optics such as e.g. the Shack–Hartmann wavefront sensor.