"The AF is faster"
That is the impression that many users are left with, when they test the new X-Pro2 that are now being displayed in many showrooms and in stores.
It is not hard to imagine that many of those that are eager to test the X-Pro2 are the X-Pro1 users. X-Pro2 has seen a major improvement in AF performance compared to the X-Pro1. So the above impression is in fact "true". But if you are comparing the speed with the X-T1, X-E2 or X-T10 (cameras with phase detection AF), then your impression is "wrong in terms of numbers, but true feeling-wise."
"The fastest AF speed"of the X-Pro2, measurement based on the CIPA guideline, is same as other cameras with the phase detection AF. X-Pro2 is not breaking the record of the AF fastest speed of the X Series.
"The fastest AF speed" is a bit tricky one. This measurement is conducted under a particular environment specified by the guideline. So the shooting scene inevitably gets detached from the real shooting environment. The score of the AF speed isn't necessarily what the users experience in reality. Therefore we say it is "wrong in terms of numbers, but true feeling-wise".
"The fastest AF speed" may be nothing but a talk, but it is good to understand the concept of it, regardless. If the Phase Detection AF is enabled, then the AF speed gets pretty close to the fastest value. If it is driven by the Phase Detection AF, then the focus lens moves by the shortest distance.
So expanding the phase detection area is first item to consider to make the AF "faster".
The X-Trans CMOS III doubled the Phase Detection area when compared with the X-Trans CMOS II. By extending the area as much as possible, most of the subject, scenery can now be covered.
It is also important to cover the weak point of Phase Detection AF. It does not work well for the low contrast subject and high frequency range subject.
The algorithm needs to be brushed up to enhance the performance. But this requires tons of work. Countless patterns, chart and scenery are considered in order to build the improved algorithm for the PD pixels on the X-Trans CMOS III. It is important to improve the accuracy, but if the algorithm pattern requires time to process, then it is meaningless. False recognition should also be avoided. Testing only help algorithm get closer to the perfection. And to process all this, X Processor Pro, which has 4x the power of the previous processor will be in place.
No matter what, there will be some circumstances where the Phase Detection AF will not work. And this is actually the most important point.
If the PDAF isn't working, then stop trying if you are using DSLR. The only solution will be MF. But in case of mirrorless cameras, it will be switched to contrast AF. If the performance of contrast AF is improved, then the AF performance as a whole will be improved.
Conan Doyle once said "A chain is no stronger than its weakest link." In case of AF, it can be said the speed of contrast AF determines the power of the AF, not the fastest Phase Detection AF.
In order to enhance the contrast AF performance of X-Pro2, the system as a whole has been looked over.
First is the X-Trans CMOS III sensor. To read the contrast, it drives at the speed of 384fps. This is double the speed of the X-Trans CMOS II, 4 times faster than the original X-Trans CMOS. And the readout signal are processed, in a timely manner, by the X Processor Pro.
Next are the lenses. In order to work with the readout and the processed signals, the microcomputer of the lenses need to be updated.
The physical parts (optical design and mechanical design) also need to be compatible with the fast readout that are driven from the microcomputer. In essence, the fast and accurate focus lens unit and actuator are required. With all this in place, fast contrast AF is realized.
Unfortunately, there are only 5 XF lenses that can receive the benefit of the fast contrast AF: XF16-55mm, XF50-140mm, XF90mm, XF35mmF2, and the XF100-400mm.
The wide angle lenses such as XF10-24mm and the XF14mm already have fast AF. We can say that the fast AF can be enjoyed through the entire focal range. Use and enjoy switching lenses that are most suitable for each scene.