I often hear students say “but I had to go to f/16, because at f/4, it would not be all sharp from foreground to background”.
False. Or rather, “it depends”. Depth of field depends on lens focal length, and distance to close object, and aperture. So at f/4, if you are not close and use a 16mm (wide angle, on a full frame camera) lens, you get:
Yeah, at f/4 you can have everything sharp, from close to far. Check the tables, etc. All sharp.
But get close, and with the very same settings, now the background is blurry:
Now, at the same settings, the background is blurry.
So keep that in mind, And also, always distinguish focus blur (above) from motion blur:
That’s because I shook the camera, and that has nothing whatsoever to do with focus or with depth of field!
I wish all my readers a very happy 2015. Love, health, happiness: everything else is secondary or can be bought. And keep shooting. And reading. See http://learning.photography for the e-books: if you have a new camera or new gear, this is the time to start using it to its full potential. Go for it. You live only once.