Major discoveries can still be made in the field of visual art, but few perhaps are quite so surprising as the current first retrospective devoted to the French photographer Camille Silvy at the National Portrait Gallery, London (to October 24).

Here is a photographer who proves to be a giant of the age, although his enormous aesthetic and commercial success took place in London in less than a decade. His entire working career lasted only about 10 years, and initially he was no more than a curious and intelligent amateur.

From 1859 to 1867, 38 Porchester Terrace, Bayswater, housed Silvy's remarkable enterprise. No fewer than 40 employees and a business partner, Auguste Renoult, were involved in a photography studio which, judging simply from 12 surviving day-books now housed at the National Portrait Gallery, produced thousands of photographs, the vast majority of which were portraits for the immensely fashionable cartes-de-visite, or calling cards, which had just been invented: when paying a call one left one's image rather than an engraved visiting card. Silvy advertised in The Times and elsewhere, copyrighted many of his images and did mail order as well as selling through London's largest photographic agency. The business was exceptionally productive, merging art with small factory methods.