4.2 Autofocus systems and modes

Autofocus systems are the unsung heroes of modern photography. They help you nail sharp shots without breaking a sweat. From phase detection to contrast detection, these systems work tirelessly behind the scenes to keep your subjects in focus.

Different autofocus modes cater to various shooting scenarios. Single-shot for still subjects, continuous for action, and hybrid for the best of both worlds. Pair these with area modes like single point or face detection, and you've got a recipe for tack-sharp images every time.

Autofocus Systems

Phase vs contrast detection autofocus

Top images from around the web for Phase vs contrast detection autofocus

• 

  Autofocus - Wikimedia Commons View original

  Is this image relevant?

• 

  मोबाइल कैमरा फोकस कैसे करते हैं | कौन सा ऑटोफोकस बेहतरीन है? View original

  Is this image relevant?

• 

  canon - How does auto focus tracking work in DSLRs - Photography Stack Exchange View original

  Is this image relevant?

• 

  Autofocus - Wikimedia Commons View original

  Is this image relevant?

• 

  मोबाइल कैमरा फोकस कैसे करते हैं | कौन सा ऑटोफोकस बेहतरीन है? View original

  Is this image relevant?

1 of 3

Top images from around the web for Phase vs contrast detection autofocus

• 

  Autofocus - Wikimedia Commons View original

  Is this image relevant?

• 

  मोबाइल कैमरा फोकस कैसे करते हैं | कौन सा ऑटोफोकस बेहतरीन है? View original

  Is this image relevant?

• 

  canon - How does auto focus tracking work in DSLRs - Photography Stack Exchange View original

  Is this image relevant?

• 

  Autofocus - Wikimedia Commons View original

  Is this image relevant?

• 

  मोबाइल कैमरा फोकस कैसे करते हैं | कौन सा ऑटोफोकस बेहतरीन है? View original

  Is this image relevant?

1 of 3

• Phase detection autofocus (PDAF) utilizes a separate AF sensor with line sensors to compare light entering the lens from opposite sides and determine focus based on the phase difference between the two images, resulting in faster and more accurate focusing especially in low light conditions (commonly used in DSLRs and some mirrorless cameras)
• Contrast detection autofocus (CDAF) analyzes contrast using the camera's image sensor and adjusts lens focus until the highest contrast is achieved, providing slower but more precise focusing that works well in live view and video modes (commonly used in mirrorless and compact cameras)

Types of autofocus modes

• Single-shot AF (AF-S or One-Shot AF) focuses once when the shutter button is pressed halfway and locks focus as long as the button remains half-pressed, making it ideal for stationary subjects (portraits, landscapes)
• Continuous AF (AF-C or AI Servo) continuously adjusts focus as long as the shutter button is pressed halfway, allowing it to track moving subjects and maintain focus, perfect for capturing action and moving subjects (sports, wildlife)
• Hybrid AF combines phase detection and contrast detection autofocus, using PDAF for quick initial focus and CDAF for fine-tuning, offering fast and accurate focusing in various situations (newer mirrorless cameras)

Autofocus Area Modes and Troubleshooting

Autofocus area modes in shooting

• Single point AF allows manual selection of a single focus point, providing precise control over the focus area, ideal for stationary subjects and portraits (headshots, macro photography)
• Dynamic or tracking AF uses a group of focus points to track moving subjects, automatically switching focus points to maintain focus on the subject, perfect for capturing action and sports (soccer, racing)
• Auto-area AF lets the camera automatically select the focus point(s) based on the scene, detecting and focusing on the closest subject, useful for quick snapshots and general photography (street photography, events)
• Face/eye detection AF automatically detects and focuses on human faces or eyes, prioritizing the closest or largest face in the frame, ideal for portraits and group photos (weddings, family gatherings)

Troubleshooting autofocus performance

1. Ensure the lens is set to autofocus mode (AF) and clean the lens contacts and camera mount to ensure proper communication
2. Use a single focus point for more precise control in low contrast situations and adjust the AF area mode to match the subject and shooting situation
3. Utilize back-button focus to separate focus and shutter release, and improve contrast and lighting to assist the autofocus system
4. In low light or low contrast scenes, use manual focus or focus assist tools (focus peaking, magnification)
5. Update camera firmware to resolve any known autofocus issues and calibrate autofocus for each lens using the camera's AF micro-adjustment feature (if available)