Earlier this year, you’ll recall, we reported that filmmaker Errol Morris, director of the Oscar-winning “The Fog of War,’’ was embarking on a movie about his longtime friend and fellow Cantabrigian Elsa Dorfman, a photographer famous for her large-format Polaroids. Well, it’s apparently done. We know because the upcoming New York Film Festival and Toronto International Film Festival announced their lineups and Morris’s movie, “The B-Side: Elsa Dorfman’s Portrait Photography,’’ is screening at both. A blurb on the NYFF site describes the 76-minute doc this way: “As this charming, articulate, and calmly uncompromising woman takes us through her fifty-plus years of remarkable but fragile images of paying customers, commissioned subjects, family, and close friends (including the poet Allen Ginsberg), the sense of time passing grows more and more acute. This is a masterful film.’’ If you weren’t lucky enough to have a portrait shot by Dorfman — Julia Child, Faye Dunaway, and Jonathan Richmanwere — that’s too bad. The film and chemicals she needs to make her pictures are impossible to get anymore, so Dorfman’s pretty much all done shooting.