When to Use Autofocus (Speed and Precision)
Capturing the perfect shot can be challenging, especially when the subject is in motion or the photographer needs to quickly adjust the focus.
Autofocus systems in modern cameras are designed to assist in these situations by providing speed and precision in achieving sharp, well-focused images.
This article will discuss when to use autofocus and how to get the most out of its capabilities.
The Basics of Autofocus
Manual Focus vs Autofocus
When capturing a photograph, ensuring that your subject is in focus is crucial.
There are two main ways to achieve that: manual focus and autofocus.
- Manual Focus: This requires the photographer to adjust the focus ring on the lens to bring the subject into sharp clarity. This method is widely used in situations where the photographer wants precise control over the focus.
- Autofocus: This is a camera feature that automatically adjusts the focus of the lens to bring the subject into clear focus. It has several modes and is especially useful in fast-paced situations where manual focus could be challenging.
Camera Types: DSLR and Mirrorless
Modern cameras generally fall into one of two categories: DSLR (Digital Single-Lens Reflex) and mirrorless.
Both of these types of cameras have autofocus capabilities, but the systems differ slightly in their implementation.
- DSLR: DSLR cameras utilize a phase-detection autofocus system, which takes advantage of the camera’s optical viewfinder. The light passing through the lens is split, and different portions are compared to determine if the image is in focus. This method allows for quick and accurate autofocus in a variety of situations.
- Mirrorless: Mirrorless cameras rely on contrast-detection autofocus. This system measures contrasts in light intensity across the frame to determine the focus area. While generally slower than phase-detection, recent advancements in technology have led to the development of hybrid autofocus systems that employ both methods, making modern mirrorless systems equally competitive in terms of speed and precision.
Types of Autofocus Systems
Phase Detection Autofocus
Phase detection autofocus (PDAF) is a popular and widely used autofocus system in DSLRs and some mirrorless cameras.
It works by dividing the incoming light into separate pairs of images and comparing them to determine the correct focus.
This method is known for its speed and accuracy, making it ideal for fast-moving subjects and sports photography.
Some advantages of phase detection autofocus include:
- Fast and accurate focus
- Works well in low-light situations
- Suitable for tracking moving subjects
However, phase detection autofocus can struggle with certain textures and patterns, which might lead to hunting for focus in some scenarios.
Contrast Detection Autofocus
Contrast detection autofocus (CDAF) is another type of autofocus system commonly used in compact cameras and mirrorless systems.
It works by analyzing the contrast in the scene and adjusting the lens focus until the contrast is at its highest, meaning the image is sharp.
Some key features of contrast detection autofocus are:
- Accurate and reliable focus in well-lit situations
- Less likely to hunt for focus on certain textures
- More suitable for still photography
On the downside, contrast detection autofocus tends to be slower than phase detection, and its performance decreases in low-light conditions.
Hybrid autofocus (Hybrid AF) combines the benefits of both phase detection and contrast detection systems.
It uses phase detection to quickly determine the approximate focus point and implements contrast detection for fine-tuning the focus.
This combination provides a fast and accurate focus in various lighting conditions and for different subject types.
Here are some advantages of hybrid autofocus:
- Speed and accuracy of phase detection
- Precision of contrast detection
- Works well in various lighting conditions
- Suitable for both still photography and moving subjects
When capturing images, choosing the right autofocus mode can greatly impact the overall speed and precision of your photographs.
In this section, we will discuss the two main focus modes: AF-S (Single-shot AF) or One-Shot AF, and AF-C (Continuous AF) or Servo AF.
AF-S (Single-shot AF) or One-Shot AF
AF-S, also known as Single-shot AF or One-Shot AF, is an autofocus mode ideal for stationary subjects.
When the shutter button is half-pressed, the camera locks focus on the selected subject.
The focus remains locked as long as the shutter button is held halfway down, allowing you to recompose the shot.
This mode is best suited for photographing:
- Portraits of people not moving
AF-S mode does not track subject movement. Therefore, if your subject moves after the focus has been locked, it might be out of focus in the final image.
AF-C (Continuous AF) or Servo AF
AF-C, also known as Continuous AF or Servo AF, is designed to track moving subjects.
The camera continuously adjusts the focus as the subject moves within the frame.
This is an ideal autofocus mode for capturing action shots or subjects that are constantly moving.
Examples of when to use AF-C include:
- Sports photography
- Wildlife photography (e.g., birds in flight)
- Children playing
To achieve the best results with AF-C, it is crucial to keep the subject within an autofocus point, as this ensures the camera can maintain focus on the moving subject.
Camera-specific Autofocus Features
- Nikon cameras offer various autofocus modes, such as AF-S (single-servo autofocus) for stationary subjects and AF-C (continuous-servo autofocus) for moving subjects.
- Many Nikon models also feature 3D tracking technology, which utilizes multiple focus points to track subjects across the frame accurately.
- Nikon’s D7000, for example, allows you to select your autofocus mode by holding down the autofocus mode selector button and turning the main command dial.
- Canon cameras have a wide range of autofocus options, including One-Shot AF for still subjects and AI Servo AF for moving subjects.
- Some Canon models, like the Rebel XS (or 1000D), enable you to select the autofocus mode by pressing the right cross key.
- Many Canon cameras are also equipped with Dual Pixel CMOS AF technology, which provides smooth, accurate autofocus during Live View and video recording.
Sony Cinema Line (Venice, FX9, FX6, FX3)
- Sony’s Cinema Line cameras include advanced autofocus technologies tailored for professional video production.
- The Venice, FX9, FX6, and FX3 models feature Fast Hybrid AF, which combines phase-detection and contrast-detection autofocus for improved speed and precision.
- These cameras also offer real-time tracking and Eye AF for more accurate focus on subjects, even in challenging shooting conditions.
Sony Mirrorless Cameras
- Sony’s mirrorless cameras are known for their advanced autofocus systems, which include features like Eye AF and Real-time tracking for both still photography and video recording.
- High-end models like the Sony A9 and A7 series employ a high number of autofocus points, allowing for more accurate subject tracking and improved focus performance in various situations.
- To select the autofocus mode on a Sony mirrorless camera, look for a dedicated AF/MF button or browse through the camera’s menu options.
Selecting Autofocus Settings for Different Scenarios
When shooting portraits, it’s crucial to have the subject’s eyes in focus.
Using AF-S (Single) or a similar mode in other camera brands is recommended.
Set your camera to Single Point Area AF mode to have precise control over the focus point.
Place the focus point on the subject’s eyes and half-press the shutter button to acquire focus.
For landscape photography, capturing sharp and clear images is the goal.
Use AF-S (Single) mode and enable Single Point Area AF or a small group of autofocus points to control which part of the scenery is in focus.
Commonly, photographers focus on a point one-third into the frame, but if your camera has focus-peaking or hyperfocal distance indicators, use them to capture the most detail.
Sports photography requires a fast and accurate autofocus system to track moving subjects.
In this case, we recommend using AF-C (Continuous) or AI Servo in Canon cameras to maintain continuous focus.
Depending on how erratic the motion is, use either a group of autofocus points or let the camera choose the points automatically.
Keep the shutter button half-pressed, and be prepared to capture images at the perfect moment.
For vlogging purposes, select a camera with reliable face and eye detection autofocus systems.
As face and eye tracking are usually enabled in AF-C (Continuous) mode, the camera can maintain focus on the speaker’s face even when they move.
Some cameras offer touchscreen focus control, making it easy to adjust focus even in mid-recording.
Adjust the autofocus settings according to your specific scenario, whether it’s taking portraits, photographing landscapes, capturing sports events, or vlogging to ensure sharp and high-quality images.
Advanced Autofocus Functions
Exposure and Aperture
Aperture is directly related to the exposure of an image, as it controls the amount of light that enters the camera.
Proper use of autofocus ensures sharp images by effectively adjusting the aperture.
- A wider aperture (lower f-number) provides a shallow depth of field, making the subject appear sharp against a blurred background
- A smaller aperture (higher f-number) increases the depth of field, making more elements in the picture appear sharp
Shutter Speed and ISO
Shutter speed and ISO play a vital role in achieving sharp images.
By understanding these settings, you can use the autofocus system to capture high-quality images.
- Faster shutter speeds, like 1/1000s, help minimize motion blur and freeze action, which is particularly useful for sports and wildlife photography.
- ISO settings are important for low-light situations as they control the camera’s sensitivity to light. It’s important to balance ISO with shutter speed to avoid camera shake and maintain autofocus performance.
|Shutter Speed||ISO||Recommended Use|
|1/1000s||400||Fast action (e.g., sports & wildlife)|
|1/60s||100||Low light, still subjects|
Focus Areas and Points
Different focus area modes allow you to control where the autofocus system concentrates its effort.
- Single-point AF: Lets you select one specific focus point
- Dynamic/zone AF: Allows you to choose a group of focus points, providing more flexibility in tracking subjects
- Auto-area AF: The camera automatically selects the focus point(s) based on the subject’s position and movement
Subject Tracking and Face Detection
Autofocus functionality has improved to include advanced subject tracking and face detection.
- Subject tracking systems keep the focus on moving subjects, ensuring sharp images even in challenging situations
- Face detection AF helps the camera identify and lock focus on a subject’s face, making it ideal for portraits
- Some cameras include eye detection AF: a more advanced form of face detection that locks focus on a subject’s eyes, ensuring perfect focus in close-up portraits
Tips for Accurate Autofocusing
Achieving accurate focus is crucial for capturing sharp images, and modern cameras offer a plethora of autofocus features to ensure optimal focus accuracy.
Let’s take a look at few tips for getting the most out of your camera’s autofocus system.
First, it’s essential to understand the two main autofocus technologies: phase detection autofocus (PDAF) and contrast detection autofocus (CDAF).
PDAF is known for its fast performance, perfect for tracking moving subjects, while CDAF excels in precision, ideal for static scenes.
Many cameras, such as those with Fast Hybrid AF, combine both technologies to achieve speed and accuracy simultaneously.
Select the right autofocus mode for your situation.
Continuous autofocus (AF-C or AI Servo) tracks moving subjects and continuously updates focus, while single autofocus (AF-S or OneShot) locks the focus once the shutter button is half-pressed.
For subjects that tend to change their position, it’s best to use continuous autofocus and subject tracking to maintain sharp images.
In low ambient light situations or when your subject has low contrast, your camera’s autofocus system might struggle to lock focus.
To improve focus accuracy, ensure adequate lighting or switch to a focus point with cross-type sensors, which are more sensitive to changes in contrast.
Another vital factor for accurate focusing is the maximum aperture of your lens.
Generally, lenses with larger maximum apertures (lower f-numbers) enable better low-light focusing, as they allow more light to enter the camera, making it easier for the autofocus system to detect contrast.
When framing your subject, be mindful of your camera’s autofocus zone.
Most cameras offer several options, such as single-point autofocus, zone autofocus, and automatic area selection. Using a single-point or zone, you can intentionally choose the focus point, providing more accurate results.
Touchscreens can be especially useful for quickly selecting the desired focus point.
Adjust your camera’s autofocus transition speed and subject shift sensitivity settings, if available.
Slower transition speeds can produce smoother focus changes in video, while faster speeds work better for quick-moving subjects.
Subject shift sensitivity determines how quickly your camera’s autofocus system will switch from one subject to another; adjust according to the motion and unpredictability of your subject.