I HAVE SUCH a passion for wrecks and reefs," says Nick Caloyianis. And he has chosen filmmaking and photography to capture the world where, he says, light changes dramatically depending on one's depth underwater, and colors achieve a "vibrancy" unknown on the surface.

Last summer his passionate work took the 30-year-old Catonsville, Md., resident to the cold, black waters of he Atlantic. There, amidst 10-foot-long blue sharks and sounding whales, he filmed Peter Gimbel's successful attempt to retrieve the treasure of the Andrea Doria.

When he speaks of the Doria dive, he mixes an engineer's seriousness with the calm bravado of someone who has come very near death and accepts that his art will take him close again.

"The Andrea Doria is 240 feet down. Everything can go wrong at that depth," he says. "The water is not (Word Illegible) down there." And even when lifted it is difficult to see. The rack of five 1,000-watt lights necessary to illuminate the murk create a white-out effect, like "snow blindness."

Caloyianis says it is hard to describe the eerie wreck. Unlike the impressions Hollywood creates of underwater wrecks, it is almost impossible to see the whole ship. It is a jigsaw puzzle, put together piece by piece inside the head. "There's only 15-foot visibility. You keep swimming. It's there.... It's there."

Lives have been lost in the wreck. The ship lies in the heart of some of the best fishing in the world and trawlers have been snagging their huge nets on the hulk since it went down 25 years ago. Those nets can trap and have trapped men and held them until they were dead. The interior of the hulk looks "as if you took a house a couple of hundred feet in the air and dropped it."

What drew him to the water? "You want to talk ancient Greek history?" he laughs. Caloyianis' people are from the island of Andros. There are divers back along the family tree and three great-uncles are sea captains.

Growing up he was a "dabbler, like many people of the time," the late '60s and early '70s. He majored in zoology at the University of Maryland, and taught diving on the side to make money.He was greatly influenced by Eugenie Clark, professor of ichthyology at Maryland.

After graduating in '73, Caloyianis spent a great deal of time in Mexico working with Ramon Bravo, a cinematographer known for his work with Jacques Cousteau. Caloyianis' work has been seen on TV in Mexico and Italy. He also worked on a Dino De Laurentiis film, "Beyond the Reef."

A filmmaking career on land doesn't appeal to him, primarily because of the expense. "Underwater you [alone] can do what an entire topside crew would do. You are the crane and dolly. That's what motivated me a long time ago, the tremendous versatility one man with a camera has underwater."

Oceanus, his underwater photography business, is totally consuming. "Everything I have is tied up in it," he says. "My camera alone cost $25,000." Not to mention his diving equipment. "Physically, it's a drain."

Physically, it's dangerous.

His second dive on the Doria last summer was in the evening. He went down with another camerman, Bob Hollis, strictly to reconnoiter. "It's bad enough during daylight, imagine what it's like at 7 at night," he says. "The currents are awesome." Both men were connected to the ship by 540-foot air-pump umbilical cords. They crawled along the deck measuring distance by lifeboat davits, one every 10 feet or so.

Caloyianis became stuck, he is still not sure in what, probably in one of the nets that cover the ship. Hollis came back to help. Hollis cut him free, and Caloyianis, swept up by the current, "took off like a rubber band into the darkness." Hollis called to the surface on his headset radio, "I think we lost Nick."

"Imagine a pilot going through a cloud with no gauges," Caloyianis says calmly. "I had no sensation of going up or down." Bringing him back in was not easy, even though he was still attached to the ship by the umbilical cord. Divers had to be brought back slowly, staying at certain levels to avoid decompression sickness, the bends. Caloyianis had no idea whether he was 10 feet or 50 feet from the surface, or if he was upside down or not.

The people on the ship were more or less able to locate him by the air bubbles on the surface. Through his headset they called to him, "Nick swim this way, now that way," and Caloyianis in the blackness tried. Eventually the surface team guided him to a cage 60 feet below the surface where the decompression process began.

In addition to a passion for the sea, what else is a good tool for an underwater cinematographer? "Well, a strong heart helps immensely."