Legendary cinematographer Haskell Wexler (In the Heat of the Night, One Flew Over the Cuckoo’s Nest, Bound for Glory) is the irascible but engrossing subject of this digital video by his son, Mark Wexler. Born rich but radicalized in the 50s, Haskell divided his career between Hollywood dramas and left-wing documentaries, adroitly combining the two in his low-budget 1969 masterpiece Medium Cool (screening Saturday and Sunday morning at the Music Box). But he was also fired from numerous projects, and his reputation as a difficult personality is borne out not only by the interviewees (Michael Douglas, Milos Forman) but by his constant second-guessing of Mark on-screen. The elder Wexler keeps insisting that he won’t sign a release for the film unless he approves of the finished product, so he must have been pleased with its brutally honest assessment of him as a gifted filmmaker who never realized his true potential. R, 95 min. Music Box.