How does phase detection autofocus work on mirrorless?

[DocS]

We all know that SLR/DSLR cameras have extra hardware (ie separate focusing screen with prisms) that carry out the phase detection.

But how does this happen with mirrorless cameras, that only have a sensor?

Is phase detection AF something that is mediated by software, and a feature that can be added by software updates like eye tracking and other specific object tracking?

 

[tbcass]

We all know that SLR/DSLR cameras have extra hardware (ie separate focusing screen with prisms) that carry out the phase detection.
But how does this happen with mirrorless cameras, that only have a sensor?

With a mirrorless camera, the PDAF points are on the sensor interspersed with the photo receptors.

autofocus - confusion about the principle of on-sensor PDAF technique - Photography Stack Exchange

Is phase detection AF something that is mediated by software, and a feature that can be added by software updates like eye tracking and other specific object tracking?

Since it's a hardware feature it cannot be added with a software update. Eye and subject tracking are done by software in the camera so yes these features can be added.

--
Tom

 

[Mako2011]

We all know that DSLR cameras have extra hardware (ie separate focusing screen with prisms) that carry out the phase detection.

They have a separate AF senor at the bottom of the mirror box that uses PDAF. It doesn't use the focus screen or the view finder prisims

But how does this happen with mirrorless cameras, that only have a sensor?

the PDAF sensors are integrated into the main sensor.

https://www.dpreview.com/forums/post/66107920

 

[bobn2]

We all know that SLR/DSLR cameras have extra hardware (ie separate focusing screen with prisms) that carry out the phase detection.
But how does this happen with mirrorless cameras, that only have a sensor?

Is phase detection AF something that is mediated by software, and a feature that can be added by software updates like eye tracking and other specific object tracking?

PDAF works by taking image samples from both sides of the lens' exit pupil to provide a parallax difference from which distance can be calculated. In a DSLR the AF unit has optics which direct light from the two different positions on the pupil to two different sensors, usually just line sensors rather than full image.

In mirrorless image sensor pixels are used for this purpose. In most systems these pixels are dedicated to AF and interpolated over when an image is captured. They are made to take light from one part of the exit pupil either by giving their microlenses a wedge profile or by masking off half of the microlens. The Canon DPAF sensors have two sub-pixels below each microlens, such that each sub-pixel gathers light from half of the exit pupil. All the sensors pixels can be used either for AF or for imaging (though the camera's specification will have a limited number of AF points). If used for AF the sub-pixels are read out separately, for imaging they are binned together.

Mirrorless AF can't give a precise distance measurement, but it can indicate which way is 'in focus' thus preventing hunting. Mirrorless AF is 'hybrid', meaning that it uses CDAF for fine tuning after PDAF has found approximate focus.

--
Is it always wrong
for one to have the hots for
Comrade Kim Yo Jong?

 

[sybersitizen]

We all know that SLR/DSLR cameras have extra hardware (ie separate focusing screen with prisms) that carry out the phase detection.
But how does this happen with mirrorless cameras, that only have a sensor?

Is phase detection AF something that is mediated by software, and a feature that can be added by software updates like eye tracking and other specific object tracking?

With a mirrorless camera, the PDAF points are on the sensor interspersed with the photo receptors.

autofocus - confusion about the principle of on-sensor PDAF technique - Photography Stack Exchange

Canon's method is different, allowing any image receptor pair to be a PDAF point:

https://snapshot.canon-asia.com/article/eng/canon-technology-explainer-what-is-dual-pixel-cmos-af

'On image sensors that are designed for Dual Pixel CMOS AF, all pixels have two photodiodes as seen in the illustration. During phase detection, the data from Photodiodes A and B are read separately and compared. During imaging, the data from both photodiodes are combined and read as one complete readout .. All pixels on the image sensor can conduct both phase detection and imaging.'

 

[DocS]

We all know that SLR/DSLR cameras have extra hardware (ie separate focusing screen with prisms) that carry out the phase detection.
But how does this happen with mirrorless cameras, that only have a sensor?

Is phase detection AF something that is mediated by software, and a feature that can be added by software updates like eye tracking and other specific object tracking?

With a mirrorless camera, the PDAF points are on the sensor interspersed with the photo receptors.

autofocus - confusion about the principle of on-sensor PDAF technique - Photography Stack Exchange

Canon's method is different, allowing any image receptor pair to be a PDAF point:

https://snapshot.canon-asia.com/article/eng/canon-technology-explainer-what-is-dual-pixel-cmos-af

'On image sensors that are designed for Dual Pixel CMOS AF, all pixels have two photodiodes as seen in the illustration. During phase detection, the data from Photodiodes A and B are read separately and compared. During imaging, the data from both photodiodes are combined and read as one complete readout .. All pixels on the image sensor can conduct both phase detection and imaging.'

And, based on that, presumably any mirrorless camera can be set up with firmware to have phase detect autofocus.

 

[Mako2011]

https://snapshot.canon-asia.com/article/eng/canon-technology-explainer-what-is-dual-pixel-cmos-af

'On image sensors that are designed for Dual Pixel CMOS AF, all pixels have two photodiodes as seen in the illustration. During phase detection, the data from Photodiodes A and B are read separately and compared. During imaging, the data from both photodiodes are combined and read as one complete readout .. All pixels on the image sensor can conduct both phase detection and imaging.'

And, based on that, presumably any mirrorless camera can be set up with firmware to have phase detect autofocus.

No as the needed supporting hardware is likely not present. You need more than just the standard sensor

 

[bobn2]

Canon's method is different, allowing any image receptor pair to be a PDAF point:

https://snapshot.canon-asia.com/article/eng/canon-technology-explainer-what-is-dual-pixel-cmos-af

'On image sensors that are designed for Dual Pixel CMOS AF, all pixels have two photodiodes as seen in the illustration. During phase detection, the data from Photodiodes A and B are read separately and compared. During imaging, the data from both photodiodes are combined and read as one complete readout .. All pixels on the image sensor can conduct both phase detection and imaging.'

And, based on that, presumably any mirrorless camera can be set up with firmware to have phase detect autofocus.

They need to be made with one microlens covering two pixels. It helps to make the pixels rectangular so that two together makes one imaging pixel.

 

[tbcass]

We all know that SLR/DSLR cameras have extra hardware (ie separate focusing screen with prisms) that carry out the phase detection.
But how does this happen with mirrorless cameras, that only have a sensor?

Is phase detection AF something that is mediated by software, and a feature that can be added by software updates like eye tracking and other specific object tracking?

With a mirrorless camera, the PDAF points are on the sensor interspersed with the photo receptors.

autofocus - confusion about the principle of on-sensor PDAF technique - Photography Stack Exchange

Canon's method is different, allowing any image receptor pair to be a PDAF point:

https://snapshot.canon-asia.com/article/eng/canon-technology-explainer-what-is-dual-pixel-cmos-af

'On image sensors that are designed for Dual Pixel CMOS AF, all pixels have two photodiodes as seen in the illustration. During phase detection, the data from Photodiodes A and B are read separately and compared. During imaging, the data from both photodiodes are combined and read as one complete readout .. All pixels on the image sensor can conduct both phase detection and imaging.'

And, based on that, presumably any mirrorless camera can be set up with firmware to have phase detect autofocus.

No, because most sensors do not have pixels with 2 photodiodes.