Auto ISO

I think this is genuinely a new Auto since the dawn of digital photography.

Back when I shot film, the ISO is fixed with the film unless you change the film back, change mid-roll otherwise you really can't change the ISO on the fly.

The settings of any film camera is likely to be Aperture Priority, Shutter Priority, Program and Manual.

Digital change this by adding ISO auto.

Often times I dial my setting to Manual so I have control on my aperture and shutter speed.  It's all about the parameters you want to let go and let the camera take control.

I set my base ISO to 64, aperture f/5.6 and shutter speed at 1/250s and WB at 2900K.  Indoor, the ISO can float up to ISO 4000 which is an ISO I can accept.  If you think you cannot accept that high a high ISO, you can set a ceiling so the ISO won't go above that even it's on Auto ISO.

I seldom do Auto ISO shooting Aperture priority, some Shutter priority if I shoot cycling races.

On "newer" camera, there is even a parameter minimum shutter speed under the Auto ISO.   This would be helpful as you don't want the shutter to drop too low if you shoot handheld or unnecessarily high.  Say if you are shooting at focal length of 200mm, in order to maintain reasonable sharpness you want your shutter speed no slower than 1/250s.  Or you can set the minimum shutter speed at Auto in which case the camera would decide what is the lowest shutter speed you can go.  There you can still tweak if you want it biased Slower (to favor slower shutter speed) or Faster or dead in the middle, I left it in the middle.

Shooting Auto ISO doesn't mean that the exposure would always be kind of correct.  If you shoot in bright daylight and set your base ISO100, Manual at f/2.8 and 1/60s, chances are your picture will be overexposed as the ISO will be out of range in the low side anyway.  The correct exposure combination is more likely to be f/16 and 1/100 at ISO100.

Auto ISO still under the "there is no free lunch rule."  Something got to give.

There are three parameters, ISO, aperture and shutter.  You can fix one, let the other two float, or you can fix two and let one float.  Or you fix all three manually.  White balance affects the color temperature which affects the color but I don't consider it part of the exposure.  Some people don't even consider ISO part of the exposure but that's up for debate...