ƒ16 is just a starting point. If you want to use ƒ11 then you need to boost your shutter speed to 1/200 (in the case of ISO100). 2.8 is 5 stops brighter than ƒ16, so you need to go up 5 stops on your shutter. In other words, a bright Sunny 16 rule- sunny day is 1/3200 ƒ2.8 at ISO 100. You can use the sunny 16 rule with any aperture you want, not just ƒ16.