This elegant, studious documentary - the first of a six-part series - leads us from ancient Rome to the Great War. Taking as its starting point the baffling natural phenomenon of camera obscura, it reveals how mathematician Henry Fox Talbot's inability to draw led him to pioneer photographic methods, and how the new discovery made a big impression on painter Edgar Degas. The early tussle to see which photographic process would gain the upper hand is a fascinating one. Though occasionally dry and prone to pseudobabble, it covers a lot of territory, and Denis Lawson's arch narration is the perfect accompaniment to some unforgettable images