A key aspect of successful landscape photography is image sharpness. Usually, it is desirable to ensure that all elements of a scene, whether close or far, are captured in sharp focus. This can prove to be challenging and, if not achieved with the click of the shutter, cannot be corrected later during post processing.
One approach that is often taken is to use the smallest aperture available, e.g. f/22, to obtain the largest depth of field. Whilst maximising the depth of field is a good intent, using such a small aperture will actually result in softer images due to an effect known as diffraction.
Most lenses are at their sharpest when used at apertures between f/8 and f/11 and whilst hypefocal focussing may allow you to capture an entire scene acceptably sharp in one image using these apertures; it is always still a compromise between a number of factors and there will be times when you cannot generate enough depth of field to capture a whole scene at optimum sharpness.
That is where focus stacking comes in.
Focus stacking is the technique of stacking (or blending) a number of images that have been focussed at different points throughout a scene to give a final image that contains the sharpest portions of the originals, seamlessly blended into one. It isn’t as laborious as it sounds and can give really good results, rendering scenes far sharper than possible in just one exposure.
In the field…
As you will be stacking the images into one, aside from the point of focus, you want the individual photographs to be identical in all other respects. Therefore, it is best to have the camera positioned on a tripod and use a remote release.
Using your optimum aperture (can easily be determined for a given camera/lens combo using focus charts, however you will most likely find that f/8 is a good starting point), take the required number of images focussed at different points throughout the frame.
A minimum of two images are required, i.e. one focussed for the foreground and one focussed for the background, however an additional third image, focussed for the middle ground can also be a good idea.