When I started out with my first DSLR about 6 years ago, I was mostly shooting with automatic exposures in "P" mode. The camera would pick a nice combination of shutter speed / aperture for correct exposure (auto ISO wasn't an option in my body yet). When I saw that some portraits I'd been shooting in bright daylight turned out to be f/11 at 1/400sec shutter speed, I decided to use "aperture priority mode" (aV) instead. It gives me the control over aperture that I want, but it's the absolute opposite of something completely "auto": it's totally fixed. The middle way is to use 'portrait mode' which will hide all the settings it chooses but pick larger apertures. It uses a bias.
On my current body (the 60D), there's an "auto ISO" function; but it too tends to be too biased
on low ISO values / slow shutter speeds. The only way to customize this auto ISO setting on my current camera is that you can set an upper limit to the auto ISO it is allowed to pick.
Since learning about the workings of these "auto" modes, I've always had the idea of factually customisable
auto ISO playing through my mind, being able to bias it manually. I've yet to see this in Canon cameras. Currently, auto ISO is coupled with "minimum shutter speed" and will always bias ISO value first, and only start to increase it when shutter speeds become really slow. The minimum shutter speed is coupled with the focal length (at least for the 5D mk2), but it's not customisable.
Now what I read recently, on the Nikon D4, was the following:
"In the D4, Nikon has (at long last) added an 'Auto' option to the minimum shutter speed options, which allows the camera to automatically set the minimum shutter speed based on its knowledge of the focal length that you're working at. This response can be biased in 5 steps, from 'slow' to 'fast' depending on whether you'd like the camera to err on the side of slower or faster shutter speeds. A small change but one that (along with the D4's extremely wide ISO sensitivity span) finally makes Auto ISO more like the 'set and forget' function that it should have been long ago."
-Barney Britton, DPReview
I think it would be great to have a customizable / auto ISO bias
setting in-camera. And having seen some of the abilities of the Magic Lantern software I'd be curious whether something like this functionality would actually be possible to make.
In aV mode (fixed max aperture), biased
auto ISO doing two things:
(A) Take a low ISO setting;
(B) keeping the shutter fast between 1/200 and 1/8000.
Now say that you could change the weight of A versus B (i.e. a low ISO having more weight, or a fast shutter having more weight), and that you could change the minimum/maximum range of B. You could perhaps even give weights to individual ISO values to be able to not make it pick the dodgy 1/3rds, or to further reduce the value of the superhigh ISO's.
Setting a fixed aperture value in aV, you'd be able to shoot with auto ISO on, with the camera picking much more useful/appropriate 'auto ISO' settings to start from. It would make Auto ISO much more useful for me in aV mode.
Action sports: give a bit more priority to fast shutters (for action, 1/1000 @ iso 400 is better than 1/250 @ iso 100). General outdoor: moderate bias on low ISO. More landscape-focused: big bias to the low ISO.
I'm not sure if this is quite what the Nikon D4 is said to do in the quote above, but I'd personally very much love to have the option of customising the auto ISO to be biased, as described here.