Filming a documentary can be tough, often requiring a great deal of planning and improvisation. One way of overcoming this long grueling path is by acquiring versatile, reliable gear. Panasonic HC-X1000 Pro, Sony PXW-FS7, Panasonic Lumix DC-GH5S, Canon EOS C100, Blackmagic Design BMPCC Pocket Cinema 4K, and Canon XF-100 are among the recommended ones. Would the cost influence your choice? I would choose a video camera that works best in low light conditions and with an autofocus capability!