At the beginning of 2014 Sony presented the A6000 to the world of photography by using the slogan „the world fastest autofocus“¹, a camera model which was aiming at the experienced user, enthusiast and the professional photographer and the first Sony camera with the new 4D FOCUS. I don’t know whether the same description for 4D FOCUS was used in the US/UK, but on the german Sony website you find (translated by author):
4D FOCUS enables outstanding autofocus performance in 4 dimensions: wide autofocus area (2D heights and width), high autofocus speeds (3D depth) and optimized predictive tracking (4D time)
This advertising message is renewed by a advertising campaing (spring / sommer 2015) with Manuel Neuer, which clearly stresses the autofocus system – reason enough for me to sound this out.
There are many articles, tests and videos out there on the internet which cover this subject and claim to demonstrate the autofocus performance. From my point of view, these tests are mainly limited on the tracking of objects moving within one plane parallel to the sensor (2D) and do not really show the capacities of the autofocus system of the Sony A6000 when the object is moving towards the camera (3D and 4D). The capabilities of the autofocus, the technical background and the optimal camera settings are covered in this article which is only referring to the Sony A6000 but also contains some valuable information for the usage of AF systems of other cameras and manufacturers.
„The world fastest autofocus“¹ is a brave slogan which will not be confirmed nor be confuted in this article because to do so, I would have to perform a comparison with a lot of different AF systems of cameras spread over the entire market. My experience with various Sony cameras (A700, A850, A55, A77, A99, etc.) and some insight into the systems used by Canon and Nikon enables me to objectively assess the AF system of the Sony A6000. Let’s move on and have a look at the technical details:
New to the autofocus modul is the 4D component – at least when it comes to the advertising slogan – which adds a predictive tracking to the focussing of an object which means a prediction of the objects next move and its direction. Not so new but important for the performance of the continuous AF is the focal plane phase detection autofocus (PDAF) with its 179 phase detection sensor elements in the Sony A6000. These sensor based PDAF elements cover 91% of the width and 92% of the heigth of the sensor which allows a very flexible usage of the different AF areas and is a big advantage in comparison of APS-C DSLRs where the AF only covers a smaller part of the image in the viewfinder. These technical limitations are even more important to full frame sensors systems, because with the same size of the AF modul its coverage of the image in the viewfinder is limited to approx. 40 %.
Putting the PDAF sensor elements on the sensor is a logical consequence and mandatory to enlarge the image coverage with AF points. This article only refers to the AF modul of the alpha 60000 and the 4D FOCUS. Sony lately published a users guide to the 4D FOCUS as download which is also available as an online version.