One of the top features to look out for on a camera these days is PDAF or phase detection autofocus.
Keep reading to learn everything you need to know about PDAF, including what it is, how it works and how it compares to conventional contrast detection AF.
What is PDAF?
PDAF is an autofocus technology that is both faster and more accurate than conventional contrast detection autofocus. The acronym PDAF stands for phase detection autofocus.
The way that phase detection AF works isn’t particularly easy to get your head around. Nevertheless, it’s worth understanding how these sensors work in order to get the most out of your camera.
To put it simply, phase detection AF works by splitting the image your camera sees into two separate images. This is done by using the prisms already found in a DSLR or on-sensor for those shooting with a mirrorless camera. The camera can tell if an image is in focus based on whether or not the two images are lined up – or in phase – with each other.
The camera also knows which split image is which. If it detects that the two images are out of phase, the camera will use this information to tell the lens which way to move to put the image in focus.
Canon explains how PDAF works in its DSLRs and mirrorless cameras in more technical terms on its website:
“Each pixel on the Dual Pixel CMOS sensor has two independent photodiodes (the parts of the sensor that record light intensity or brightness). The camera’s processor compares the signals from the two photodiodes, and if they match, it knows that this area of the image is in focus. If there is any deviation between them, it looks at pairs of photodiodes across a group of pixels, and can then calculate which direction the lens needs to be adjusted to achieve sharp focus, and how much focus adjustment is required”.
All of the above happens in a matter of milliseconds, making the autofocus process quite a bit faster than contrast detection AF, a method that uses contrast to determine which section of an image needs to be sharp and adjusts the focus from there.
Contrast detection AF can still be very accurate, but it doesn’t compare to phase detection when it comes to speed, making PDAF the superior option for tracking fast-moving subjects and key for sports and wildlife photography.
PDAF is also the stronger choice for abrupt shifts in focus, like moving the focus point from an object at the front of the frame to one at the back, or vice versa. Using PDAF makes this transition much smoother and snappier than doing so using contrast detection AF.
