How Af-S Lenses Report Focus Distance To Camera

The focus modes on a camera allow you to select a single focus point for static elements or to continuously adjust the focus for moving subjects. The three most common focus modes are:

- AFS (Auto Focus Single): This mode is designed for capturing still subjects. The camera focuses on the subject when the shutter button is pressed halfway down and locks the focus until the picture is taken.

- AFF (Auto Focus Flexible): AFF is a hybrid mode that combines elements of AFS and AFC. It continuously focuses on the subject as long as the shutter button is held halfway down. If the subject starts moving, it automatically switches to AFC.

- AFC (Auto Focus Continuous): AFC is intended for capturing moving subjects. The camera continuously adjusts the focus as long as the shutter button is held halfway down, allowing you to track and capture subjects in motion.

Single autofocus mode (AF-S / One-Shot AF)

AF-S is one of the least intelligent AF modes. If you’ve acquired focus on your subject and it moves, the camera won’t adjust the focus to compensate. You’re locked into using your current focus, and if your subject moves, you’ll have to focus again.

AF-S is a good choice for landscape photography, along with narrow apertures that give a wide depth of field for maximum sharpness. It is also useful for creating long exposure images to ensure that your focus is correct.

Single autofocus mode is available in the following nomenclature:

• Nikon: AF-S Mode
• Canon: One-shot AF
• Sony: Single-shot AF

Continuous autofocus mode (AF-C / AI Servo)

Continuous autofocus mode, also known as AF-C or AI Servo, is one of the main autofocus modes in photography. This mode is ideal for capturing moving subjects, as it allows the camera to continuously track the subject and adjust focus accordingly. In this mode, the focus is not fixed and locked to a specific point. Instead, the camera locks onto the subject and moves the focus point with the subject, even if it moves.

When using continuous autofocus, it is possible to make the tracking area smaller, which can increase the autofocus speed. This mode is particularly useful for capturing fast-moving subjects, such as in sports or wildlife photography. It is also beneficial when shooting portraits, as it can help keep the eyes in focus.

However, it is important to note that continuous autofocus mode is not as efficient as single autofocus mode when the subject is static. It also requires more processing power and lens adjustments, resulting in higher battery consumption. Additionally, this mode may not always work perfectly due to limitations in camera technology.

To use continuous autofocus mode, you need to set your camera to AF-C (for Nikon) or AI Servo (for Canon). Sony cameras refer to this mode as Continuous AF.

Hybrid autofocus mode (AF-A / AI Focus AF)

The Hybrid autofocus mode (AF-A / AI Focus AF) is a combination of the Single autofocus mode (AF-S / One-Shot AF) and the Continuous autofocus mode (AF-C / AI Servo). This mode is useful when you are unsure whether to use the single or continuous autofocus mode.

The Hybrid autofocus mode is best used for challenging subjects, such as wildlife and small children, who move in sudden bursts of speed and then pause. The camera detects subject motion and switches to the AF-C mode to track them. Once the subject pauses, the camera switches back to the AF-S mode.

The constant micro-adjustments made during the AF-C mode can be problematic once the subjects stop moving. Hence, the Hybrid autofocus mode is the best choice when the subject's movement is unpredictable.

Manual focus mode (M)

Manual focus mode is also useful when you want creative control over the focus. For example, when trying to achieve a dreamy, blurred background effect.

Manual focus is also beneficial when the subject is heavily backlit, as the autofocus may get confused.

Some photographers also prefer to use manual focus for macro photography so that they can have precise control over where the narrow blade of focus lies.

Manual focus mode is also useful when you are having trouble getting your focus to lock, for example, in very low-light situations.

Different camera brands have different names for manual focus mode. For example, Canon uses the abbreviation "MF" for manual focus, which should not be confused with "M" for manual exposure mode.

Active vs passive autofocus

There are two types of autofocus (AF) systems: Active and Passive. The "Active AF" system works by shooting a red beam at the subject, then bouncing that light back to the camera to calculate the distance between the camera and the subject. The "Passive AF" system, on the other hand, uses either Phase Detection or Contrast Detection to detect contrast.

Active AF

• Active AF systems measure distance to the subject independently of the optical system.
• Active AF systems can use ultrasonic sound waves or infrared light to calculate the distance.
• Active AF is generally less accurate than Passive AF.
• Active AF will not work through windows or on surfaces without contrast.
• Active AF may not focus on subjects that are very close to the camera.

Passive AF

• Passive AF systems determine correct focus by performing passive analysis of the image entering the optical system.
• Passive AF does not direct any energy towards the subject.
• Passive AF can be achieved by phase detection or contrast measurement.
• Passive AF may not find focus when the contrast is low or in low-light conditions.
• Passive AF is dependent on a certain degree of illumination.

Active vs Passive AF

Active AF is generally used for stationary, non-moving subjects and only works for close subjects. Passive AF, on the other hand, is more versatile and can be used for both moving and stationary subjects. It is also more accurate than Active AF. However, Passive AF may struggle in low-light conditions or when there is little contrast in the scene.

Frequently asked questions