Originally Posted by Nick911sc

When you shoot wide open, you get more of a DOF so the center is in focus but as you move away from the center you begin to get out of focus. So if you're shooting wide open at say.. 1.8 as you move away from the center it will begin to lose sharpness and if something is further away you'll get the blurring(bokeh) in the photo. So if you take that same lens and boost the F/ to 4 more of the image will be in focus including things that may be further away from the focusing point. The mm of the lens itself does not really effect DOF. If you shoot at 90mm with 2.8(like my macro shots or at macro 1:1 with a higher F stop which is a totally different lesson lol) you're getting that same DOF effect.

IMO an external flash increases picture quality 10 fold. But natural light I find better obviously in situations like shooting cars.