Focusing technique is always critical in macro photography. Depth of field is very shallow even at small apertures, and must be used to best advantage by placing the subject in an optimal manner within the depth of field envelope. Autofocusing may not work with a macro set-up, so be prepared to focus manually if necessary. Whether using manual or automatic focusing it is important to know on which part of the subject focus should be critically adjusted.
When working with extension tubes or bellows, the focus setting of the lens is relatively unimportant because the movement of the lens is small by comparison with the extension. Focusing is therefore generally achieved by moving camera or subject, or adjusting the bellows.
When focusing manually it is often very helpful to fit a right-angled viewfinder. This piece of equipment makes working overhead and close to the ground much more convenient. Manual focus may be easier to achieve when the whole camera and support assembly is moved back and forth relative to the subject. A focusing rail is extremely useful when the camera is tripod mounted because it facilitates precisely controlled movement of the equipment. A good focusing rail offers transverse movement on a quick release mechanism, and a smooth geared slider for movement in the vital longitudinal plane for accurate focusing.
Autofocus is unlikely to provide a satisfactory means of focusing when working with a hand-held camera. Hand movement will be sufficient to cause the mechanism to shift focus continually. It is therefore generally better to set the required focusing distance manually and then move the camera to achieve focus as in the tripod mounted situation described above.