5.6 is not 4 stops, it is more like 1 1/3 stops.
9 is about 1/3 stop more.
Bill MN wrote:
After the bird flew away I found I had to set the camera from F9 to F5.6, that's 4 stops before it was set right in manual. I was shooting through a patio window which was tinted and not the cleanest so that didn't help. Lucky I got anything but the D7100 is a fantastic camera for the price.