The impact interaction of a solid sphere against an initially plane gas-liquid interface is experimentally studied with a new experimental principle. The interface is formed at the bottom of a capillary of about 8 mm inner diameter. The sphere impacts the interface inside the capillary. The new principle is based on video imaging of the grey levels of the gas-liquid interface using light beam reflection. The grey levels are recorded by a CCD high-speed video system. Collision time is determined as the time between the first two maxima of the grey levels and obtained by means of Fourier analysis. The dependence of collision time on the diameter and density of impacting particles is investigated and compared with the available theoretical models. The experimentally determined collision time is longer than the collision time predicted by the available theories. The reasons for this disagreement are discussed. The disagreement may be affected by the dependence of the restoring force on the radius of the plane gas-liquid interface.