EOS 70D: Dual Pixel CMOS AF explained
The EOS 70D has been designed for photographers who are keen to explore and expand their shooting possibilities. It is equipped with a range of Canon technologies that make it possible to capture a wide variety of scenes and subjects in outstanding quality. Central to this ability is world-first, Canon-engineered Dual Pixel CMOS AF technology. Please click on the image above for a short film explaining the technology and benefits and read on for a detailed account of how this system works...
What is Dual Pixel CMOS AF?
Dual Pixel CMOS AF is a sensor-based, phase detection Auto Focus (AF) technology designed to provide smooth, high-performance focus tracking in movies and fast autofocus acquisition when shooting still photos in Live View mode.
It is a unique, Canon-developed technology, ideal for creating professional-looking pull-focus effects and keeping a subject moving towards the user in sharp focus while maintaining a blurred background – a defining characteristic of EOS Movies.
Thanks to this groundbreaking advance, capturing a subject and retaining sharp focus, even when moving, has never been easier.
Why was Dual Pixel CMOS AF developed?
With the ability to make a subject stand out with a limited depth-of-field, comes a requirement to keep control over focus, if the main subject moves or the point of focus changes. Dual Pixel CMOS AF was developed so that control of focus during movie making is made easier and smoother – removing the perceived notions that a DSLR’s movie mode is usable only to a professional. Additionally, Dual Pixel CMOS AF was developed to enhance the usability of shooting with Live View – moving even closer towards the same performance encountered when using the viewfinder.
The EOS 70D includes a high resolution Vari-Angle LCD that can be used to shoot a range of subjects from unusual and creative angles. A phase-detection auto focus system supports photographers and expands the range of subjects that can be captured.
How it works
The EOS 70D features a newly-designed Canon APS-C CMOS sensor with 20.2 million pixels. All effective pixels on the surface of the EOS 70D’s sensor consist of two individual photodiodes, which are read separately for phase-detection autofocus and together for imaging. Dual Pixel CMOS AF is possible over 80% of the width and height of the Live View frame and is highly accurate without compromising on image quality.
Unlike other methods of sensor-based autofocus, which allocate either autofocus or imaging functions to pixels on the sensor, the pixels on the EOS 70D’s CMOS sensor can be used as imaging pixels and phase detection AF pixels. As a result, no additional imaging processing is required around pixels dedicated for AF, which ensures both quick acquisition of focus and maximum image quality.
To perform phase detection on the image plane the EOS 70D reads left and right photodiodes independently and then calculates the phase-difference of the two parallax images.
By using this phase-difference AF technique the EOS 70D predicts the position the lens is in focus and moves it. By contrast, the more conventionally used contrast AF method looks for the focal position while moving the lens back and forth, so AF speed ends up being slower and not as smooth.
With face and object tracking engaged, Movie Servo AF follows a chosen subject as it moves, or when you recompose a shot. Alternatively, just select different focus areas by simply by tapping the touch-screen when recording.
At launch, Dual Pixel CMOS AF is compatible with 103 current EF lenses, spanning EF and EF-S, fixed focal length, wide-angle and telephoto lenses. The system marks a significant advancement in autofocus performance with greatly improved AF speeds.
Please click here for a list of lenses that have limited compatibility with the Dual Pixel CMOS AF system.