There’s a lack of focus to this documentary about the rise of digital filmmaking, partly because director Christopher Kenneally seems unsure of who his audience is. Average moviegoers? Tech geeks? Hollywood insiders? He’s certainly lined up an impressive list of talking heads, many of whom are at the forefront of this transition: Martin Scorsese, Steven Soderbergh, James Cameron, George Lucas and David Fincher, along with a host of legendary cinematographers. (If Keanu Reeves seems a bit out of place as the interviewer/host, it’s not for his lack of enthusiasm.) As a film critic, I could have used more movie-specific discussions of the aesthetic implications of celluloid versus digital, rather than a recent history of digital cameras, but then again maybe I don’t belong to any of Side by Side’s various audiences.