WHAT’S THE GREATEST SKILL a cinematographer needs? “Having a strong bladder,” quipped Alwin Kuchler (Steve Jobs) in a rare moment of irreverence among six top directors of photography. In fact, that could be the easiest part of the craft, as DPs now are required to navigate increasingly powerful directors, studios that can alter their work on a whim and the pressure to employ digital effects so heavily it becomes almost another job — which is why Robert Richardson (The Hateful Eight), 60, argues it’s time for separate Academy Awards categories: one for old-school cinematography and the other for work with heavy effects. He and Kuchler, 50, were joined by Danny Cohen (The Danish Girl, Room), 52; Linus Sandgren (Joy), 43; Masanobu Takayanagi (Black Mass, Spotlight), 41; and Mandy Walker (Truth),…