Pixel Perfect wrote:
I agree, and it's great to finally see AF points that are x-type at f/5.6.
In the previous 1D-series bodies, most points were either linear f/5.6 or a mix of f/2.8 and f/5.6 cross-type.
The EOS 7D was the first camera to employ cross-type sensors that were f/5.6 in both directions, as far as I am aware.
When an f/5.6 AF sensor looks through an f/5.6 lens, it operates within f/5.6 depth of focus precision, which is adequate since the lens itself is f/5.6.
When an f/5.6 AF sensor looks through a lens faster than f/5.6, the sensor will operate, but the resulting depth of focus precision *may* not be sufficient to achieve accurate AF, especially if the exposure occurs at a very fast f-number, such as f/1.2.
When an f/2.8 AF sensor looks through an f/5.6 lens, the incident light does not have the phase separation to resolve the focus to the required precision; thus, the sensor is disabled by the camera. If you trick the camera by preventing the body from reading the f-number of the lens, it will attempt to use the AF point anyway, which may result in erratic performance or inability to confirm focus.
When an f/2.8 AF sensor looks through an f/2.8 lens, it operates with additional precision over an f/5.6 sensor.
With this in mind, we see why it is important to have cross-type sensors with the same f-number sensitivity in each direction, as this permits consistent AF performance regardless of the orientation of the camera. We also see that although f/5.6 sensors have greater applicability across various lenses, they lack the precision of f/2.8 sensors, even if they are cross-type. The ideal situation would be to have both f/2.8 and f/5.6 cross-type sensors, enabling accurate AF performance when using fast primes, as well as good tracking performance for lenses slower than f/2.8, where the f/2.8 sensors would not function.
And so, if this latest news is true, it would seem that Canon has listened and devised an entirely new AF system that not only combines these types of sensors, but also introduces f/4 cross-type points to further improve versatility and performance across the EF lineup. This is very encouraging news for those who are waiting for a 5D-series update, because the existence of this AF system means that there is now significantly more room for an upgraded AF system in the future 5D(3). I am hopeful that some of the goodies that we see in this 1D X will also find their way into the 5D-series.