> >With these settings, I'd expect the ISO to hit 3200 before the >shutter speed starts slowing down. > >However, what I see when I depress the shutter-release halfway >is an ISO of 1600 and a shutter speed of 1/80 s. > >To get the camera to use an ISO of 3200, I had to set the ISO >to 3200. > >What am I mis-understanding?
Standard Auto ISO is disabled when using the scene modes. You lose control of the camera settings in the scene modes and the cameras computer sets the controls to what it considers best for the scene used and the lighting conditions.
You'll find that if you turn off the scene mode and turn off Auto Iso, when you go back into scene mode you'll get the same shutter speed and ISO setting as when you had Auto ISO on.
If you want to use Auto ISO and get control of your other settings don't use scene modes.
You might find it helpful to refer to the table that begins on page 321 of the manual, Available Settings, especially so if you use a lot of Scene modes.
The table will show you exactly what settings are user adjustable in every mode. Notice that in the "Shooting menu" section, the "ISO sensitivity settings" row shows a "4" footnote for every one of the scene modes. That footnote denotes Auto ISO control not available.
Keep this table in mind for reference if you get other unexpected settings results when using scene modes.