WHEN Scottish photographer Lindsay Robertson attended an artists' retreat in Florida three years ago, he chanced upon a representative of George Eastman House International. A photography museum based in Rochester, New York, it owns a number of prints by iconic snapper Ansel Adams, arguably the father of the genre in which Robertson has plied his trade since the 1970s: landscape photography. The result of that meeting is Celebration Of Genius, a huge exhibition occupying three floors of Edinburgh's City Art Centre and featuring 150 of Adams's best-known and most significant photographs. Although shot entirely in black and white, they are in fact a symphony of grey, cream, shadow and light.

It is the exhibition's only UK showing and its presence in Scotland is a coup both for Edinburgh and Robertson, whose work shows alongside that of his hero. The only other picture not by Adams is one taken of him by Arnold Newman in 1976, at Adams's home in Carmel, California. Then in his mid-70s, he is shown leaning against a door, his thick-rimmed glasses pushed back on his head, a rubber apron covering his body and an old-fashioned beard fringing his chin. Were it not for the impish grin and the broken nose - a childhood injury incurred during an earthquake - he could be an Amish patriarch on his way to a fetish convention.

It was 60 years earlier, in 1916, that Ansel Adams saw Yosemite National Park for the first time and, using a Kodak No1 Box Brownie, took his first landscape. He was 14, scion of a wealthy Californian clan and already decided on a career as a pianist. A year later he joined the Sierra Club, the group once headed by Scottish-born environmentalist John Muir, and which he himself would later lead.

Adams would return to Yosemite repeatedly throughout his career, finding in its awesome majesty a subject he could never tire of studying. Accordingly, the core of the exhibition is the landscape studies he made there and, later, in places like Death Valley and the Joshua Tree National Park. His 1927 portfolio, Parmelian Prints Of The High Sierras, is seen here in its entirety for the first time and visitors can compare the most famous of its 18 images - titled Monolith, The Face Of Half Dome - with a 1960 gelatin print Adams made himself.

The titles of the images evoke not only the place they were taken but the hardships their author endured to capture them in the first place. Look at Moonrise From Glacier Point, for instance, which shows sharp, forested peaks silhouetted against an almost full moon as eerie fingers of cloud intrude from the left. Then picture Adams hacking for miles through the undergrowth in the dead of night with several kilos of equipment on his back, looking for just the right place, waiting for just the right time.

Perhaps it's no surprise, then, that there's a sense of morbidity in many of the images. Adams was fascinated by nature's ability to form abstract patterns, but consider the gnarled, arthritic trees he photographed or a suite of close-ups of crosses in churches, and you have to wonder to what extent he delighted in death and disease. One of his most famous photographs is Moonrise, Hernandez, New Mexico, from 1941. It is life-affirming in its stark beauty but in composition it is ghoulish: a sickly moon floating over a graveyard, an adobe church to the left, a scree of shadowy vegetation in the foreground and ghost-like clouds slashing the image in two. Meanwhile, a photograph of an eclipse taken in 1939 is entitled Black Sun, Tungsten Hills. It sounds like two bands on a death metal bill.

Even his man-made subjects seem to reek of catastrophe and misfortune. He shot a suite of photographs in California that he called his Shipwreck Series - rusted anchors, twisted and torn bits of metal - and found beauty in wallpaper stained with water, shot in close-up and turned into abstract art.

Adams once said: "There are always two people in every picture: the photographer and the viewer." In his case that's mostly true and it's worth remembering as you walk round Celebration Of Genius. But occasionally there are three people in the contract because, though not known for his portraiture, Adams did make studies of people and 13 examples are on display. They range from documentary-style images of Mexican women in their pueblos to portraits of female friends whose bobbed hair and 1930s clothes are in stark contrast to the timeless quality of the landscapes. The most interesting portraits are of two photographers who are almost as famous as Adams: Alfred Stieglitz, shot in 1939, and Edward Weston, captured in 1945 sitting on the roots of an enormous tree. None is what you would call playful, however; there is no levity in Ansel Adams's art.

BUT these are not the oddest images in the exhibition. That honour goes to Antelope House Ruin, from 1942. It shows a tumbledown house dwarfed by the wall of rock against which it is built. The insubstantiality of the ruin against the immovable weight of the cliff face - ugly, beautiful, grey - is off-beat enough, but at the base of the rock someone has painted a huge swastika in white paint.

What Adams's images invoke most is a sense of smallness, of humility. In the dim light of this municipal gallery - kept on the gloomy side to preserve the integrity of these precious prints - his pictures are as blatant an invitation to contemplate God as you are ever likely to receive. I don't know his own view on that subject; I do know he believed deeply in his art and that to him it was both challenge and obligation, something (as he once said) "to help us see more clearly and more deeply, and to reveal to others grandeurs and the potential of the one and only world which we inhabit". Conservation of this world, rather than contemplation of the next, seems to have been his preferred option.

Perhaps the saddest image, then, is the one that ends the exhibition, Rails And Jet Trails, Roseville, California. Taken in 1953 it shows railway tracks bending into the distance while overhead a series of jet trails seem to mimic their arc. Adams shot it into the sun but uses a steel upright to block the light, turning it into a thin blasphemous finger pointing straight up. Coming from an arch-conservationist like him, the critique is obvious. There were no vapour trails across Yosemite's wide open skies in 1916, he seems to say. He lived for another 30 years after that picture was taken but, despite his years of seeing nature in the raw, I can't help wondering if it was in this image that he saw his own mortality signalled most clearly.