This is new to me. I don't know if the 1DsIII has auto ISO.

With alt lenses, I've found I like to put ISO in "A" and set exposure control Tv. Set shutter to a desired setting. Shutting with a wide zoom indoors I set it to 30.

So the camera sets the ISO to what it needs. The advantage of this over Av is it avoids needing to stop to raise ISO. It doesn't mater what the lens aperture is set at, as it's metering what's coming through the lenses. I think.

Anyway, I'm always looking for a faster way to use alts. This meets the need for a minimum shutter speed.

you could be on to something here.