Film Reviews: Having dealt at length with China’s “anti-rightist” campaign in his epic documentary “Fengming: A Chinese Memoir,” Wang Bing continues to probe the devastating consequences of this little-aired historical chapter in his first narrative feature, “The Ditch.” A brisk jaunt at 112 minutes compared with Wang’s three-hour “Fengming” and nine-hour “West of the Tracks,” this powerful realist treatment offers a nevertheless brutally prolonged immersion in the labor camps where numerous so-called dissidents were sent in the late 1950s. Result makes for blunt, arduous but gripping viewing that will be in demand at festivals, particularly human-rights events, and in broadcast play.