What is Phase Detection Autofocus How do PDAF works
What is Phase Detection Autofocus How do PDAF works

Phase Detection Autofocus, PD Autofocus in Smartphones, Drawbacks of PDAF, How PDAF (Phase Detection Autofocus) works, What is PDAF

Cameras are essentially built with sensors, a control system, and a motor. Autofocus came into the picture to resolve the blurry image issue caused by incorrect focal measurements. Autofocus technology corrects the badly focused image by being reliable on sensors to locate the correct focus.

Many inventions later, Autofocus was distinguished to active, passive, and hybrid AF (Autofocus) sensors. Phase detective Autofocus (PDAF) was built based on a passive Autofocus sensor.

As opposed to active AF using, infrared or ultrasound waves to measure the distance of the subject, the passive Autofocus uses phase detection, contrast sensors, or both. However, few do make use of infrared light when there’s not enough light.

Most of today’s smartphones and DSLRs cameras are equipped with this technology and are more or less believed as the fastest technology that measures the object in focus.

Let’s see how PDAF technology works!

How does PDAF (Phase Detection Autofocus) works?

With evolvement in photography technology, the innovative ideas are endless which in turn raises doubts in people. If one has to understand in simpler terms how PDAF operates, let’s dig into the DSLR technology.

  • Cameras are equipped with two mirrors and two microlenses.
  • The first mirror is the main reflex mirror and the second one is the small secondary mirror.
  • The captured light from the opposite side of the two microlenses enters the main mirror, which is then reflected on the secondary mirror.
  • The PDAF sensors come into play after the light passes from the secondary mirror.
  • The light from the secondary mirror is directed to the PDAF sensor, which directs it to the group of sensors.
  • Usually, two sensors are installed for one AF point. The images from the sensors are then evaluated by the camera.
  • If the images obtained are not identical, the PDAF sensors instruct the lens of the camera to adjust accordingly.
  • Until a correct focus is configured, this process gets repeated several times.
  • As soon as the correct focus is achieved, the AF system recognizes that and sends a confirmation that the tracked object is in focus.

Autofocus issues arise if the distance between the lens mount and the camera sensor and the distance between the lens mount and sensors are not identical. Although the explanation for this is lengthy, all this happens in a fraction of a second and is hence considered the fastest technology.

PDAF in Smartphones

Although the PDAF technique is widely used in DSLRs, several smartphone brands have made use of this functionality in their smartphones.

It takes around 0.3 seconds to compare the images passing through the lens. Unfortunately, smartphones cannot be equipped with two PDAF sensors. Hence it comes with something known as ‘Photodiodes‘.

The photodiodes are masked to allow light from only one side of the lens giving the smartphone two images to compare and focus. If the image obtained is not in focus then the sensors enable a lens to make necessary changes.

Drawbacks of PDAF:

  • Sensor alignment issue is a major problem if the manufacturers have not installed the PDAF software since the sensors are then one’s instructions camera to make necessary changes.
  • Low lighting issues might not allow PDAF sensors to focus the image correctly.
  • Time-consuming while trying to get the lens to focus using wide apertures.

All in one, PDAF works wonderfully well while trying to capture the subject in movement as it is superbly fast. Allows to capture portraits and still life photography in an incredible way. Overall, Phase detection AF is faster and more accurate than traditional contrast AF.

With smartphone photography trending as a new hobby, many peoples are going for phones that come with PDAF sensors.