We all know that aperture is one of four factors that control depth of field. Almost all the time, landscape photographers want the entire scene to be in sharp focus, so high aperture values are used.
In addition to the aperture, the hyperfocal distance will also greatly impact the decision of what aperture is necessary. Hyperfocal distance is a subject worthy of its own post, but you need to know that if your subject is far enough away, you can achieve full depth of field independent of what aperture is used. So the first consideration is how far away the subject is. If you’re shooting a sunset and the closest part of the scene that you include in the frame is 200 feet away, you could probably get away with a high aperture value of f/11, for example.
But if you follow my advice on composition and include a clear foreground subject, you will need a higher aperture value to compensate for the fact that you will be focusing much closer to the camera. If you have a foreground object very near to the camera and a wide scene in front of you, you might have to go as high as f/22 for full depth of field.
You might also remember having seen some of your lenses going much higher than f/22. Some lenses allow an aperture as small as f/40! So why limit yourself to f/22? Diffraction. At high aperture values, diffraction causes the photo to be soft. Diffraction occurs when light passes around sharp edges (such as those of an aperture), which deflect the light rays and cause irregular light patterns. All high apertures will cause some diffraction, but a general rule is that diffraction becomes too severe to control at f/22 on many lenses.
So why does your specific lens matter? Because the focal length affects depth of field. Keep in mind that your camera will also affect the correct depth of field. A so-called “crop” sensor camera will have more depth of field than a 35mm equivalent sensor camera if all else is equal.
Now that you understand SOME of the factors involved in determining what aperture should be used for landscape photography, let’s set down a couple VERY GENERAL RULES THAT ARE NOT CORRECT IN EVERY SITUATION.
If you’re using a wide lens (10-25mm) on a crop frame camera, and you have a foreground element close to the camera, you might consider an aperture of f/18. This will allow for solid depth-of-field and acceptable sharpness on many wide-angle lenses.
If you’re using a wide lens (10-25mm) on a crop frame camera, and you do NOT have a foreground element, consider an aperture of around f/11 or f/16.
I hope this post gives you a good starting place to understand the what aperture to use for landscape photography. Keep in mind that there are many factors involved in this decision, but I hope this at least lays a groundwork for your understanding.