This exquisite exemplar of deep-focus nonfiction cinema testifies that observational work is alive and well. Our hero, the 14-year-old Ola, is tasked with looking after her brother, Nikodem, as he prepares for his communion. Nikodem’s autistic tics soon become just a small part of a memorable character who’s both mischievous and irreverent. First-time director Anna Zamecka demonstrates her knack for capturing subtle gestures: Ola jostling her brother as he sits uncomfortably in a pew, their mom assembling a crib in an agitated state — and the siblings are seriously good at playing themselves. A capricious, Lonergan-esque tragicomedy, Communion delivers on a great Polish tradition of character-based documentaries. It also reminds us that most teenagers are ready for any challenge.(PS)Preceded by a provocation from Destiny Watford