A few people have bought a Leonard Nimoy photograph without knowing who Leonard Nimoy is. Most likely they are migrants who arrived here through a wormhole from the Gamma Quadrant, where "Star Trek" reruns have yet to penetrate. Nimoy, who for more than 40 years was Spock, the pointy-eared, half-Vulcan science officer on the Starship Enterprise, has been an accomplished photographer for nearly that long, and his work has been collected by several museums. He has been taking pictures since he was 13, when he developed them in the family bathroom in Boston's West End. In the early '70s he studied at UCLA with Robert Heinecken, a conceptual photographer so rigorous, Nimoy said recently, that he thought if you happened to see a body falling from the sky, you would be wrong to take a picture of it unless you were already embarked on a study of objects moving through space. Anything else was mere photojournalism.