>>3884890The factor you’re missing is EV comp.
When using any sort of modern autoexposure system, there’s a separate exposure compensation (EV comp) setting. If you want the shot to be brighter or darker vs what the meter thinks, you dial that in with the EV Comp setting.
So in a hypothetical situation, imagine that you want to micromanage your aperture because depth of field is extremely important compositionally. You don’t care about your shutter speed as long as it’s hand-holdably fast, and you care even less about your ISO but you want it as low as possible while giving you a bright enough scene given the other two variables.
If you use aperture priority with auto ISO, you get exactly that. EV comp let’s you shift the brightness up and down for your exposure, and the camera figures out whether it can trade ISO or shutter speed for you.
With most auto iso systems, you can set your minimum shutter speed so that you can have a faster one if you’re shooting fast action or a slower one if you’re shooting static subjects or you can just let the camera peg it to your focal length.
I leave it on basically any time I’m not shooting with off-camera flash (where the meter has no idea how much light is eventually gonna be there) or on a tripod (where I usually want to just have the lowest iso and shutter speed be damned).
This means you can get your shot usually by adjusting zero or one exposure settings. Sometimes two, but it’s rare. So the mental energy you would otherwise have to spend on setting your three exposure variables for every single shot can instead be spent on making sure you get the best composition.
