Dept of field or dof is one of the landscape photographers best tools for creating art photos. What is dept of field (dof) ? A landscape photo that is tack sharp from the flowers in the foreground until the horizon has a large dof.  The opposite example is typically a picture of a flower or a person where only the flower or persons face is in focus and everything else is blurry. In that case the photographer has used a shallow dof to emphasize the main subject of the photo. A skilled photographer can master and control the dof before capturing an image.

How to control and master dof:

The depth of field depends on the focal length of the lens and the f-stop used. The longer focal length a lens has, the shallower dof. Portrait photographers typically uses lenses from 85mm and larger to throw the background behind the subject out of focus. A landscape photographer typically uses focal lengths from 15mm-35mm.  Wide angle lenses can be used to create a large dof for landscape photos.

The other important factor is the f-stop or “aperture” used when capturing an image. The f-stop is a number referring to the built-in iris of the lens. The larger f-stop number, the smaller iris will be used when capturing the image. A large f-number gives a small iris and more depth of field.
Modern SLR-cameras can be set to capture images in aperture (f-stop) mode. I use the aperture-mode for landscape photography. In that way I can pre-select the preferred f-stop, and the camera calculates the exposure time. It is also a reliable camera mode for HDR-photography because all the captured images in a HDR series of exposure will have the same dof.

How to calculate dept of field in landscape photos:

First you need to know about the hyperfocal distance. Lets say you have set your camera to aperture mode, selected f11 and have a 35mm lens. Your mission is to capture a lovely landscape art photo with maximum depth of field. The hyperfocal distance is the nearest distance you can focus on and still get objects at infinity acceptably sharp. The hyperfocal distance must be set using manual focus, and the larger f-stop number used, the shorter the hyperfocal distance can be set. This way you will get the maximum dof in your captured landscape scenery. There are many tools on the net and also apps that calculate dof. Dofmaster have several free programs to calculate the hyperfocal distance and dof at their site.
The hyperfocal distance for a full size 35mm sensor in the above example can be found on this page. The correct answer is 12 feet.  I calculated the dof with an app named Field Tools, and the depth of field will be from 6,2 feet to infinity when the camera focus is set to 12 feet, the hyperfocal distance.