I have been reading "Understanding Exposures" , which is a good book btw. In the book, the author metions a technique for shooting backlight, snow, or sunset. What you do is that you meter the sky to get your aperture and shutter speed first then recompose to get a proper exposure. What confuses me is that he likes to meter the sky with an 2.8 aperture, and adjust the shutter speed accordingly. Then it comes to recomposing. A bigger aperture number, say 16, is neededfor landscape, so aperture is adjusted to 16 (5 stops) and the shutter speed needs to be decreased by 5 stops accordinly for the correct exposure. My question is: Why do we need to meter the sky at aperture 2.8 instead of the aperture we need, 16,at the first place? Does it give a better metering result? thanks!