Originally posted by Srhphoto The focus system is able to determine the rate of change of distance relative to the camera and hence can 'predict' where to focus the lens to.
AF prediction isn't magic. It needs data from the AF and a history of movement information, as
Canon says:
"With a predictive AF system the camera is continuously recording the position of the subject and predicting where it will be for the next frame based on its motion so far."
I've found (on paper) that the K-3/ K-3 II AF options look very similar to
those of a 1Dx or 5D3 [PDF 430k].
The Pentax terminology may not match Canon, but the basics seem similar - eg Pentax says:
"PENTAX Real-time Scene Analysis System accurately detects the color, shape and movement of a subject, and keeps monitoring it throughout the imaging process"' Canon says:
''
To achieve the goal of optimum AF in diverse situations and lighting conditions, the EOS-1D X makes use of far more than just an autofocus sensor, as previous EOS cameras have done. Instead data is collected from the 61-point AF sensor, the auto exposure sensors, an AF correction light-source detection sensor and, with certain lenses, a panning detection gyro sensor. While these sensors provide a benefit to One-Shot AF shooting, the major benefit is found with AI Servo, where they can help identify the subject by not only contrast, but also colour. "
The Canon menu on, for example, the 7D2 certainly does, however, give the appearance of more control over AF tracking behaviour, but once again you can see similar concepts (AF hold behaviour, for example) at work in the K-3 settings. As the Canon 1 Dx docs themselves imply, earlier Canon's that just relied on the AF sensor alone couldn't really do AI servo predictive.
The key Canon concept with AI Servo 'predictive' AF - like with Nikon's '3-D tracking' predictive AF - is the integration of data from the various camera sensors - metering, AF, light source, gyro, focus distance (eg Canon has a list of lenses that work better than others in some AF modes, Nikon says G series lenses work best), panning mode etc etc - to make the AF algorithms more intelligent. In particular, better information to work with contrast and colour in moving subjects. This is what the Pentax K-3 system has also set out to achieve.
The Canon and Nikon AF systems are more evolved, esp on their pro bodies, but you can see Pentax is heading in the same direction.