With each new dizzying invention, our screens – and our lives – seem to slip ever deeper into uncharted territories of virtual and augmented realities. But step back a moment… taking a long view of the history of moving images, film has always been reinventing itself, each new innovation remaking the medium and changing its – and our – relationship with the world. In this unique event, curators of the BFI National Archive each take up the cudgels to champion great game-changers of the past that, they will argue, have profoundly affected film as it is today. Colour, 16mm, CGI… which one will get your vote?