What is focusing?
Focusing means adjusting the distance at which the subject is rendered sharply. This can be done automatically using autofocus (AF) or manually with the focusing ring on the lens.
Press the shutter-release button halfway and the camera uses autofocus to focus on the selected focus point. Autofocus is therefore the most commonly used focusing method for many photographers.
There are, however, situations in which manual focusing provides greater control or in which autofocus has difficulty identifying the correct subject.
From autofocus to manual focus
Many lenses have a switch that allows you to choose between automatic and manual focusing.
When manual focus is selected, you use the focusing ring on the lens to determine exactly which part of the subject should be sharp.
The photograph shows a Nikkor lens. The M/A setting means that autofocus is active but the focus can still be adjusted manually when necessary. In the M position, focusing is performed manually using the focusing ring.
Be careful: M on the lens and M on the camera
The M setting on the lens does not have the same meaning as M mode on the camera. Selecting M on the lens disables the lens's autofocus.
M mode on the camera stands for manual exposure. You set parameters such as aperture, shutter speed and ISO yourself. Even when the camera is in M mode, autofocus can still be used if the camera and lens are configured for autofocus.
When autofocus focuses on the wrong subject
Autofocus is fast and accurate, but it can sometimes focus on the wrong part of a subject. This may happen when the active focus point is no longer positioned exactly over the intended subject.
Modern cameras often provide multiple focus points and several AF-area modes. By deliberately selecting the appropriate focus point or AF-area mode, you can control more precisely which part of the photograph should be sharp.
If you want more control over when the camera focuses, autofocus can be separated from the shutter-release button. This technique is known as Back Button Focus. Autofocus is then activated with a separate button on the back of the camera, while the shutter-release button is used only to take the photograph.
When should you use manual focus?
Manual focusing means using the focusing ring yourself to determine where the plane of focus lies. It is particularly useful when autofocus is not sufficiently reliable or when you want precise control over which detail is sharp.
When there is insufficient contrast
Autofocus requires contrast or recognisable details to focus accurately. In low light, fog, on uniform surfaces or with subjects that have very little contrast, autofocus may have difficulty finding a reliable focus point.
Some cameras have an AF-assist light that temporarily illuminates the subject. If autofocus continues to hunt for focus, manual focusing may be the better solution.
With Live View, you can magnify the image on the camera's LCD screen. This often makes very precise manual focusing possible.
Macro photography
In macro photography, depth of field is often extremely shallow. Even a very small change in focusing distance can determine which detail appears sharp and which appears blurred.
Manual focusing provides considerable control in macro photography. With the camera on a tripod, you can magnify the Live View image and focus accurately on the desired detail.
Night and evening photography
In low-light conditions, insufficient contrast can make it difficult for autofocus to focus correctly. Manual focusing can then be a useful alternative.
If possible, use Live View and magnify the image to focus accurately on a bright star, lamp or another high-contrast detail. A tripod is recommended when using long shutter speeds.
Portrait photography
In portrait photography, focus is usually placed on the eye closest to the camera. Many modern cameras provide eye detection or Eye AF specifically for this purpose.
With a wide aperture and therefore a low f-number, depth of field is limited. Accurate focusing on the eye then becomes particularly important.
Manual focusing can be useful when complete control is required, but modern Eye AF systems are often faster and very accurate for portrait photography.
What is focus stacking?
Focus stacking is a photographic technique in which several photographs taken at different focusing distances are digitally combined into a single image with a greater depth of field.
The camera should preferably remain in exactly the same position throughout the sequence, usually on a tripod. For each photograph, focus is moved slightly from the nearest part of the subject towards progressively more distant areas.
The number of photographs required depends on factors including magnification, aperture, focal length and the depth of the subject. A few photographs may be sufficient for some subjects, while macro photography may require dozens or even hundreds of images.
The sharpest areas of the individual photographs are then combined using suitable software. The result is a single photograph in which a larger part of the subject appears sharp than would normally be possible with one exposure.
A small aperture can also increase depth of field, but extremely small apertures may reduce maximum sharpness because of diffraction. Focus stacking therefore allows you to use a more favourable aperture while still achieving a large depth of field.
Focus stacking example
What is focus bracketing?
Focus bracketing is the automatic capture of a sequence of photographs in which the camera changes the focusing distance slightly between each exposure.
Focus bracketing should not be confused with exposure bracketing. With exposure bracketing, the exposure changes between photographs; with focus bracketing, the focusing distance changes.
The sequence created with focus bracketing can subsequently be combined using focus stacking. Focus bracketing therefore creates the individual photographs, while focus stacking combines them into the final image.
Not every camera provides a focus bracketing function. Cameras that support it often allow you to select the number of photographs and the size of the focus step between successive exposures.
This technique is widely used in macro and product photography when a large depth of field is required without using an extremely small aperture.