Photo finish.

In east London, a Victorian warehouse has been transformed and dedicated to photographic endeavour.

Metro Imaging is a Laboratory for professional photographers and its services range from straightforward photographic processing and printing to electronic scanning and manipulation of images. The firm's success made new premises necessary.

In designing Metro's new headquarters, Munkenbeck & Marshall have taken cues from the nature of the business - as they are adept at doing - expressing linked themes of light and communication while remaining within a robust Modernist-inspired architecture of their own devising. The four-storey building was one of the few unlisted Victorian warehouses in a conservation area and the architects were able to make some structural innovations. The most spectacular part of the scheme is a daylit studio for hire on the roof, a great glazed airy space with its profile derived from the imposing mansard roof.

The two floors beneath are devoted to offices and electronic imaging respectively, straightforward enough except for the presence of a Crosfield scanner protected from the atmosphere by a minimalist glass enclosure. Darkrooms are cloistered in the basement.

A luminous reception area with a transparent shop window - glass panels spanning existing bays - gives on to Clerkenwell Road. Metro wanted its technical operations to be, and to be seen to be, accessible to their customers. The interior at this level is layered horizontally back from the glazed facade to expose the laboratorial guts of the business to public view. This has been achieved by means of a void that cuts through the centre of the building along its width and rises from the basement to the height of the second floor. Behind it, the ground floor has been replaced by two mezzanines so that the slice reveals a stack of four laboratories, like illuminated stages, closed off by near-invisible panels of glass. They are connected by zig-zagging metal stairs and an appealing little goods lift that whirs up and down sparking light. Standing at the entrance you can watch people moving around and between the levels. Remote from this sectionally described activity, it is as though you were looking through a lens.

The practice's detailing is always enjoyable (see their restaurant, AR December 1993 pp31). Here, attention is caught by reception desks built of illuminated glass bricks, stainless steel and granite; by the elegance of the minimal balustrading and by the display system devised for photographic exhibitions across the glass facade. The same underlying themes - transparency and light - are powerfully expressed in the design of the vehicles of communication, a glass lift and stairs of perforated metal in a glazed tower. The lift car is standard, but fitted with glass walls within a glass and steel shaft it becomes a moving conductor of light.

On the roof, the structure defining the studio is a response to the problem of how to admit as much daylight as possible without it becoming uncomfortably hot. Because this is primarily a photographic studio, solar glazing which affects the quality of light could not be used and a constructional solution was devised. The roof is in two parts: on the north side, it is transparent and composed of a diagonally braced tubular steel structure with V-shaped elements curving in two dimensions and springing from posts, the glazing panels being glued to tubular steel purlins; the south opaque part is a curving thickly insulated sandwich broken by a rectangular skylight. This was positioned by computer calculation to throw afternoon light over the shooting wall on the east - the angle naturally depending on the season.

The air-conditioning system is similarly inventive, though its effectiveness was hard pressed during this summer's heat. Cold air percolating through every fourth panel of the handsomely veneered Micro-floor rises to the height of the photographer, calculated at roughly 2m, and is extracted at this height and re-circulated.

Hot or not, this is an exhilarating space with its long views over the City of London and north towards Islington's heights. P.M.