Video cameras and dslr have different names for the same thing.
My observation is that iso 100 on a dslr corresponds to 0db gain on a video camera.
Then, each time you double the iso, it is equivalent to a 3db gain in the video camera.
iso gain db
I know this is an old post, but I wanted to reply in order to add some clarity to the subject. Especially since this is the first thing that comes up when you Google search nx5u and ISO.
Camcorders generally don't use ISO settings but they do have what is known as a native ISO. This is the default sensitivity of the sensor at 0db.
Using a light meter, i can confirm the native ISO for the Sony NX5U is 800. This is because a native ISO of 50 or even 100 would be too dark for interiors and 800 gives you better indoor options while the built-in ND filters give you options for shooting outside.
I generally shoot at -3db which is equal to 400 ISO.