In both of them you choose an iso, and the camera automatically set shutter speed and aperture. So what's the difference?

I'm using Canon EOS 4000D, where there is only Program AE (mode P), but I've seen ISO priority in other cameras. So I was wondering about the difference, if there is any.

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    \$\begingroup\$ What camera/brand? \$\endgroup\$
    – xenoid
    Commented Apr 14, 2023 at 11:40
  • \$\begingroup\$ Canon EOS 4000D \$\endgroup\$ Commented Apr 14, 2023 at 11:51
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    \$\begingroup\$ I've encountered "Auto ISO", but not "ISO priority". Can you name a camera with this mode, just for reference? Thanks \$\endgroup\$
    – osullic
    Commented Apr 14, 2023 at 12:58
  • \$\begingroup\$ Don't remember the camera, but I think you are right on the fact it was called "auto ISO" \$\endgroup\$ Commented Apr 14, 2023 at 13:28
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    \$\begingroup\$ Well, then that's a totally different question. Auto ISO is where the camera chooses the ISO (possibly within user-set bounds), according to some algorithm. It can be used together with any of the PASM exposure modes. Personally I shoot in M mode together with Auto ISO - it allows me to set the aperture I want, and then influence the camera's choice of ISO by easy manipulation of the shutter speed. \$\endgroup\$
    – osullic
    Commented Apr 14, 2023 at 13:55

1 Answer 1


I've never seen a camera with an ISO priority mode; but I've often mentally called Programmable Auto (P) mode exactly that, since you are choosing your ISO and the camera can shift all the other settings around to get to good exposure.

"Auto ISO", however, is a completely different thing. Auto ISO is where the camera can select the ISO setting, usually bounded by limits you set. So, the ISO setting is not given priority and locked down, as aperture and shutter settings are in aperture-priority and shutter-priority modes, respectively.


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