Don't know if this will apply but you might want to look into it. When I was trying to figure out why my point and shoot gave me much better pix than my 5100, I found that with the build in flash, the 5100 ran the ISO straight to 3200. There is a setting on the 5100 that limits how high the camera can set the ISO on its own. Don't know if the 3200 has this but you might want to look into it. It might just do the same thing with video. Or, perhaps you set the shutter speed so high that the lens, at wide open, doesn't let in enough light so the only other thing the camera can do is adjust the ISO. Just some thoughts.