Canon Dual Pixel CMOS AF

Canon Dual Pixel CMOS AF is a proprietary autofocus technology developed by Canon Inc., first introduced in mid-2013 with the Canon EOS 70D DSLR. It represents a major advance in autofocus design by integrating fast, accurate phase-detection autofocus directly on the image sensing plane.^[1]

Overview

Dual Pixel CMOS AF enables every imaging pixel on a supported CMOS sensor to perform both phase-detection autofocus and image capture. Each pixel is split into two independent photodiodes (side-by-side or top/bottom), allowing the camera to compare light arriving at the two halves for phase detection, and then combine the full signal for image output.^[2]

Unlike earlier systems that used separate AF sensors or sparse on-sensor AF pixels, Dual Pixel allows autofocus across a wide central area – about 80% of the frame in early implementations (e.g. EOS 70D) — with later mirrorless models realizing nearly 100% frame coverage.^[3]

Technical Background

• On-sensor phase detection: By reading signals from both halves of each pixel, the system computes focus error, direction, and magnitude — just like traditional PDAF — eliminating switching delays between contrast-detection and phase-detection.^[4]
• High coverage and speed: Since almost all pixels contribute to autofocus, the system offers millions of potential focus points, yielding smooth and responsive focusing in live-view and video modes.^[5]
• Image quality preserved: Because autofocus is integrated at the pixel level rather than using dedicated non-imaging pixels, there’s no penalty to image quality from autofocus processing.^[6]

Limitations

• Low-light constraints: Performance may degrade in dim conditions; tracking speed and accuracy depend on sensor sensitivity and firmware algorithms.
• Canon-only system: Dual Pixel technology is proprietary; competing brands use different hybrid autofocus systems.
• Complexity: Advanced versions (Dual Pixel AF II with machine-learning tracking) may require configuration to optimize tracking settings for specific scenarios.^[7]

Applications

Dual Pixel CMOS AF is widely used in:

• Live View photography on DSLR and mirrorless bodies, for fast subject acquisition
• Video and cinema use, where smooth autofocus transitions, consistent tracking, and face/eye/animal detection are crucial
• Hybrid workflows benefiting from fast autofocus in both stills and motion imaging ^[8]