Landscapes: Focusing Tips
In contrast to wildlife portraits, landscape photographs should generally be as sharp as possible from front to back. To maximize the depth of field, choose a short focal length lens (< 50 mm) and small aperture opening. But be aware that stopping down the aperture has limits. Beyond f/16, the loss of image detail from diffraction begins to outweigh any benefit from increased depth of field. Diffraction is an optical property of all lenses, but only becomes noticeable with very narrow aperture openings.
Having a large depth of field does not mean that everything will be perfectly in focus. If you focus on the background, the foreground is likely to be somewhat blurry. And if you focus on a subject in the foreground, the background is likely to be soft. To get as much of the scene as possible in focus, a simple rule is to focus about a third of the way into the scene (not halfway, as you might expect, because the depth of field is always larger behind the focus point than in front of it). A variation on this approach is the double distance rule. Estimate the distance from the camera to the closest object you want to be sharp, then focus on a point that is twice that distance. Phone apps are available for more precise depth of field calculations.
Keep in mind that objects within the depth of field will be “acceptably” sharp, but not maximally sharp. The only part of the image that will be in perfect focus is the spot where you place the autofocus point. Image sharpness invariably drops off as you move away from this point, to a greater or lesser degree. Therefore, if there is an object in the scene that you want to be tack sharp (say like an animal), you should focus on it and accept the effects this has on the overall depth of field.
It is good practice to use a tripod for all your landscape photography. By eliminating camera shake you can slow down the shutter speed to achieve a narrow aperture and a low ISO setting, even in relatively low light. Keep an eye out for plant movement because of wind; this may require boosting the shutter speed to prevent motion blur.
A more advanced technique for maximizing sharpness across the entire image is focus stacking. With your camera on a tripod, take two or three shots (or more) while focusing progressively farther into the scene. The sharpest parts of each image can then be blended into a single image using specialized software.