When the San Francisco Museum of Modern Art reopens May 14, it will devote more space to exhibiting photographs than any other art museum in the U.S.

Following a nearly three-year, $305 million expansion, the museum will have 14 galleries spanning 15,000 square feet exhibiting photos—more room than the photography galleries of New York’s Metropolitan Museum of Art and Museum of Modern Art combined. On top of that, the museum has created a new study area for researchers called the Pritzker Center for Photography and added...