Our innate fascination with each other and with the minutiae of our lives - witness the voyeuristic appeal of the current reality TV shows - is ideally suited to the penetrating examination of the camera lens. Close scrutiny, when pushed to its extremes, verges into territory that tests social boundaries, and in the case of some of the works in Cruel and Tender, makes for uncomfortable viewing.

Yet Diane Arbus’s 1960s and 70s portraits of transvestites, giants, dwarves and others on the margins of society are presented with a dignity that invites empathy and curiosity rather than revulsion. Boris Mikhailov’s unblinking portraits of the down-and-outs of Kharkov are more disturbing to encounter. He spends many hours with his subjects, learning their stories and gaining their trust. Like Arbus, Mikhailov argues that such images bear witness to a reality that cannot simply be ignored.

Rineke Dijkstra’s portraits of bullfighters and of women who have recently given birth leave her subjects with no room for evasion. Despite this, the individuals pictured retain their self-composure and meet our gaze. Philip-Lorca diCorcia’s subjects, meanwhile, are literally ‘caught in the lens’. His radio-activated system allows him to photograph passers-by from a distance, catching them off-guard, and revealing the solitary state of the individual in the crowd. A candid approach is also adopted by Martin Parr, whose snatched images amount to a technicolour catalogue of dubious taste and excessive consumption.

Antecedents for these different approaches can be traced in the work of August Sander and Walker Evans. In his catalogue of the German peoples, Sander created a category for ‘The Last People’, which included stark portraits of the disabled and dead; while Evans’s own compendium of American life featured a series of images taken on the subway, shot unobtrusively with a concealed camera.