OSPDAF
OSPDAF -- On Sensor Phase Detect Autofocus -- a feature in some digital sensors where the main imaging sensor has, unlike separate PDAF module in AF SLR cameras, though some DSLR cameras have both. For DSLR it is not that important, because it affects only video & liveview mode. For mirrorless camera it is much more important.
These pixels would require to be interpolated in the image output. There are "left looking" and "right looking" pixels Some sensors have more than one group of AF pixels, which group is used depends on imaging lens exit pupil location.
Variants of arrangement
- entire rows dedicated (early Nikon 1)
- 45 degree grid
- honeycomb grid
Dual Pixel AF is a variant where there are two diodes under common microlens, so it requires no interpolation. Apparently Canon licenses the technology only for smartphone sensors where they do not compete with Canon products.
Image artifacts due to OSPDAF pixels
Due to non-uniform pixel angular response, grainy texture can appear https://www.dpreview.com/forums/thread/3912663 https://www.dpreview.com/forums/thread/4259940
Sometimes OSPDAF pixels can be seen in reflection from sensor if there is a flat glass before the lens https://www.dpreview.com/forums/thread/4178735
History
- 2010 Fujifilm releases with compact camera F300EXR with OSPDAF
- 2011 Nikon releases its Nikon One line of mirrorless cams with 1" sensor (manufactured by Aptina) having quick AF
- 2012 Sony releases NEX-5R & NEX-6, AF improvement deemed insignificant by many users
- 2013 Sony cross-licenses patent portfolio with Aptina
- 2013 Canon releases EOS 70D with Dual Pixel AF
- 2014 Olympus E-M1
- 2014 First in smartphone -- Samsung Galaxy S5
- 2016 Canon releases first PDAF in a FF camera (EOS 5D Mark IV)
Links
Sensor Phase Detect Autofocus in an article on DailyTech.com
