Understanding Aperture – camera fundamentals
The shorter the focal length (wider field of view, e.g. 18mm, 35mm, 50mm, —->, 600mm) the greater the DoF. If you shoot a 18mm lens at f/11 pretty much everything from 1-2 meters to infinity will be in focus. You shoot a 600mm lens at f/11 (depending on distance to subject) your DoF may only be a centimeters to a meter. Technically, it is the magnification of the subject that effects DoF. In other words if you got really close to someone and filled your frame with their face with an 18mm lens at any given f-stop you would have the same DoF as you would if you were far away and used a 600mm lens creating the same magnification. But again for ease of explanation I will present it this way since beginners tend to think of lenses on their own.
This scan of an older slide was taken in the Granite mountains of the Mojave National Preserve looking east towards the Providence mountains. It was shot at f/11 on a 20mm lens. Notice how all the elements in the photo are sharp, from the barrel cactus in the foreground to the distant clouds and mountains at the ‘infinity’ focus range. Scenic photography generally tries to maintain as great a depth of field as possible.