I'm still not really sure when Auto ISO would be useful then. I thought that no matter what, the ISO would always stay within the range I had it set, with the shutter speed going no lower than what I had the minimum set at.
If if did that (shutter speed limit), it would be limited, causing unnecessary exposure failures. If you want a specific shutter speed, then set a specific shutter speed.
Camera A or P mode says to adjust shutter speed as necessary.
Auto ISO says to adjust ISO as necessary.
If both, it does both.
It is NOT a Minimum shutter speed. You set shutter speed elsewhere. This is in the Auto ISO settings, and it is the "minimum shutter speed" before ISO is adjusted upwards. A threshold setting. Just a matter of wording maybe.
The purpose is because Auto ISO must hit some physical limit before ISO is increased. For example, in camera S mode, the aperture hits its wide open value before ISO is increased. But A and P modes adjusting shutter speed, that shutter maximum is 30 seconds. This shutter setting in the Auto ISO menu just substitutes another more reasonable limit, so ISO can increase before shutter speed gets to the end at 30 seconds. Seriously.
Call it Minimum Shutter Speed Before Adjusting ISO. It is in the Auto ISO menu.
I was surprised to hear it went higher than Maximum ISO, so I just ignored that, not knowing about it. I cannot see that, cannot duplicate it here. There would be no need, since shutter speed CAN drop to 30 seconds. I don't know what happens at 30 seconds?
Was this ISO in camera Manual mode? In camera Manual mode, I know ISO can go lower than Minimum ISO, if necessary for the exposure. It is still Auto ISO in camera Manual mode, but it cannot adjust shutter or aperture then to help do it (so the range is small, and it may take more liberties to pull it off).