With conventional phase-detection AF, the light that enters through the photographic lens is divided into two images. The difference in the focus point position between the two images is measured on a dedicated AF sensor rather than the image sensor itself, enabling the camera to determine the direction and amount of lens adjustment required to obtain proper focus. Because phase-detection AF enables fast focusing performance compared with contrast-detection AF, the technology is widely employed in digital SLR cameras, mainly for viewfinder shooting.
Dual Pixel CMOS AF employs the same measurement principle as a dedicated AF sensor, except that it is carried out directly with the image sensor. Its large coverage area enables smooth and reliable image-plane phase-detection AF for both still images and video with no reliance on dedicated AF sensors or contrast-detection AF.
Contrast AF is an autofocus method employed in compact digital cameras and video camcorders, as well as conventional digital SLR cameras for Live View shooting. Because contrast is highest when an image is in proper focus, the camera analyzes the contrast information from the image on the image sensor, adjusting the lens until the maximum contrast value is reached. While contrast AF offers high focusing accuracy, it tends to require more time compared with phase-detection AF because the focusing components of the lens must be driven during AF measurement to find the point of peak contrast.
Hybrid CMOS AF and Hybrid CMOS AF II
Hybrid CMOS AF is an AF method employed in the EOS Rebel T5i Digital SLR camera and the EOS M digital camera that delivers enhanced focusing speed during Live View shooting and when shooting video. Combining fast phase-detection AF and high-accuracy contrast AF, Hybrid CMOS AF makes possible faster focusing performance than contrast AF alone, quickly measuring the subject distance using a dedicated phase-detection AF image element embedded in the CMOS image sensor and completing the process with extreme accuracy using contrast AF. The EOS Rebel SL1 camera features Hybrid CMOS AF II, which makes use of an imaging sensor that supports AF across a wide area spanning approximately 80 percent of the shooting area measured vertically and horizontally.