As the sun escaped its dark clouds on a wintry Sunday at 10 a.m., a heavy mist, like liquid silver, slowly rose, revealing a vain goose admiring itself in the looking glass of ice on the Chesapeake and Ohio Canal. The goose might have thought he owned the morning, the canal and the mist, but he was caught forever in the camera lens of Sir Robert Cotton.

Sunday mornings -- after the coded cables, the diplomatic pouch and the black-tie dinners were taken care of for the week -- Cotton, then ambassador extraordinary and plenipotentiary for Australia, would put on his old clothes and go out to shoot geese with an Olympus OM2N camera. Almost every Sunday, from 1982 through 1985, Cotton, often accompanied by his wife Eve, would troop along the canal looking for fleeting moments to stop on film.

Cotton has returned to his home in Australia, but he's left behind a photographic record of those Sundays on the canal, on exhibit through May 11 in the ground floor gallery of the Phillips Collection. In more portable form, his photographs, together with a text by Jane Weinberger, have been published as a book by Weinberger's tiny Windswept House Publishers.

"Photography for me is completely relaxing," said Cotton. "With golf, you tend to play with people you do business with, and it continues. But with photography, you can wear old clothes and totally relax, concentrate on the scene. While I was ambassador, I worked every Saturday, but I kept Sunday for photography."

Photography took at least one of the same qualities as diplomacy -- patience. Cotton said he went back four times in summer and winter, working out the light with the help of a compass, to make "Lock Eight," which shows the lock keeper's white stone cottage looking at itself in the still waters of the canal, sheltered by a tree that looks like an umbrella.

To an eye accustomed to color television, glossy magazines and the ultranatural color of plastic doodads, the intensity of Cotton's black-and-white photographs will come as a surprise.

Every detail is etched so sharp and crisp, the depth of field so great, that you have the illusion of seeing the C&O Canal through an old-time stereopticon or through 3-D movie glasses. Cotton said he achieved this effect by using his Olympus OM2N with Ilford FP4 film and most often an f16 stop. None of the pictures is cropped; all are direct enlargements from the negatives.

He gave up on color photography in 1978, he said. In his preface to the book he explained that he quit making slides when he reached 5,000 because they "had the usual facility of sending people to sleep who looked at them, particularly after dinner."

His first photographic study was of Broken Hill, an Australian mining city 800 miles from Sydney. For several years now, Cotton has concentrated on photographing a certain theme to make a single-focus exhibition.

Over the years, he exhibited in many group shows. Finally, in spring 1984, he had a one-man show of his diplomatic travels called "Footsteps" at Meridian House here. "Footsteps" has been shown in many places since.

Today, the former ambassador aims his light meter at Palm Beach, a long stretch of beach overlooked by his house north of Sydney. Life and the light measure just right.