Radio Frequency Corona ignition systems represent an interesting solution among innovative ignition strategies for their ability to stabilize the combustion and to extend the engine operating range in lean conditions, with respect to conventional spark ignition systems. In this work the effects of the Corona ignition have been analysed on a single cylinder optical engine fuelled with gasoline, comparing the results with those of a traditional single spark ignition. The impact of the Corona ignition on combustion stability has been studied focusing on stable, near-limit, and unstable conditions, increasing the air-fuel ratio starting from stoichiometric conditions. The natural luminosity (chemioluminescence) of the premixed flames has been recorded by means of a high speed camera, synchronized with the cycle-corresponding indicating analysis results. The high speed imaging allowed to observe the early flame development, providing information not obtainable by the conventional combustion analysis based on indicated pressure data. The analysis of the cycle-resolved equivalent flame radii highlights a significant increase of the flame speed in all the operating conditions when Corona ignition is adopted, besides a lower standard deviation of flame radius growth. The indicating results show an extension of about 0.25 lambda units of the engine stable lean limit, with consequent significantly reduced emissions of nitrogen oxides (NOx), in the part load operating point investigated.