I watched the Phillip Bloom video and wondering the same thing. I just finished doing some some research on ISO ( http://petapixel.com …when-shooting-dslr-video/ )
This is what it said:
"Basically, the camera has several native ISO settings, in most cameras these are 100, 200, 400, 800, 1600 etc. The thing with the values in the middle (125, 160, 250, 320) is that they are simulated! This is very important to understand.
If you set the ISO at 125, there will be more noise than at ISO 100 because the camera sets the ISO at 100 and than simulates the higher ISO (125) by applying GAIN.
Similarly, when set at ISO 160, the camera actually already goes for ISO 200 and applies NEGATIVE GAIN, making the image darker and thus hiding a lot of the noise."
I'm still confused a bit by all of this