Catherine Opie’s show at the Guggenheim, which provides an overview of this important photographer’s work since 1991, would be a required pit stop on any visual-arts lover’s tour at any time of the year. But place it against all the hoopla surrounding California’s Proposition 8, and the survey acquires further resonance because the questions at the center of Opie’s work are, What is community? What’s “normal”? How do you define it? Who defines it, for that matter, and for what purposes? In a weird way, it’s like a high-art complement of those HSBC’s “your point of view” ads in which the same image is tagged with opposite descriptives.The show’s full title is “Catherine Opie: American Photographer,” a statement bold in its simplicity, because many of Opie’s subjects over the years have been pulled from what some still consider to be not only outside the American mainstream, but downright un-American. Lesbians, transgender persons, the S&M underground: Opie, a great formalist who knows her art history (she once made a spectacular self-portrait in which she nurses her son in a Piéta-like pose, for instance) has captured them, often in carefully posed and lighted portraits—this is very far from the “raw” aesthetics one often associates with this type of subject. In the mid-90s series “Domestic,” she showed lesbian families and couples; in the recent “In and Around Home,” the openly gay artist turned the lens to her own family. The overall impression is both great dignity and great banality.The show also allows us to see all the people on display are equally American, from surfers lost on a calm gray sea to S&M afficionados, and all deserve to be considered with the same inquisitive, respectful eye—all make up the American landscape. The very notion of “outsider” is questioned with appealing matter-of-factness. A self-described humanist, the artist simply says “We are all together in this as a species” in a video interview posted on the Guggenheim site.