Famed portrait photographer Elsa Dorfman stepped out from behind her oversized camera long enough this week to speak at the Harvard Book Store about “Elsa’s Housebook: A Woman’s Photojournal,” which was originally published in 1974. The book chronicles, in black and white, the many friends — some of them famous, such as Allen Ginsberg, Peter Orlovsky, Gary Snyder, Gregory Corso, and Robert Creeley — who visited Dorfman at her place in Cambridge in the late 1960s and early 1970s. There’s also a picture in the book of Dorfman’s then-boyfriend Harvey Silverglate, the well-known civil rights attorney who eventually became her husband and was sitting in the front row at Dorfman’s talk at the bookstore.