AF-C performance (Tracing in low light situation)
A99II is perceived to be a combination of best image quality (A7RII) and AF performance (A77II). The following is a typical test for AF-C performance. Focusing on a fast approaching subject at night is very challenging even for top-ranked action camera.
Referring to the following GIF sequence reveals, A99II is not perfect, some of the pictures are slightly out of focus. However under such challenging situation her keeper ratio still maintains around 70% which should be good enough for most photographer. Besides A99ii hunts and misses several shots when the truck is turning, I think it is having a hard time to struggle a focus point.
You may visit my flickr to view the full-size sequence
Selecting the right AF mode
There are six AF modes in A99ii namely Wide, Zone, Centre, Flexible spot, expand flexible spot and Lock-on AF. If you are Sony A-mount and E-mount user, those AF modes should be familiar to you. Here is my experience:
(1)Wide: It gives the widest AF coverage and surprisingly its AF accuracy is higher than I expected (same as Dpreview finding). However you leave the camera to decide where to focus thus it is only useful when (1) background and subject can be clearly separated e.g. blue sky & flying Black kite (2) In urgent situation if you have no idea where to focus or even unable to use the viewfinder, then you need to leave A99ii to decide the AF point.
(2)Zone: This mode will divide the entire AF coverage into 15 zones. Unless your subject is large enough to fill the zone area or otherwise this mode will often lead to misfocus as it may incorrectly focus on the surrounding. A similar mode called Group AF can be found in Nikon system however its accuracy is much higher than Sony. The zone mode is not useful for me.
(3)Centre: Practically it is a centre spot AF. If I need a spot AF, I will rather choose flexible spot.
(4)Flexible Spot: It gives the highest AF accuracy and flexibility because you can choose precisely where to focus e.g. eye ball. However (1) the spot area covered is too small and will lead to hunting or even misfocus if the contrast of that spot is low; (2) although the newly introduced joystick of A99ii helps alot, it is impractical to shift the spot during high speed shooting. I found this mode very useful in taking still and portraiture.
(5)Expand flexible spot: It is a flexible spot mode with 8 surrounding AF points expanded. As the name implied, the AF area is expanded so that you will have higher opportunity to acquire focus on your subject. The drawbacks are (1)same as zone AF, misfocus will happen if your subject is not large enough to fill the expanded area; (2) it seems to me the AF calculation will be averaged among the expanded AF points so that it can’t give a 100% sharp image.
(6)Lock-on AF: This mode is supposed to be an outstanding feature inherited from A77II. It works great and the AF accuracy is reasonably high. However when compared to D500, the 3D tracking capability of Nikon DSLR still prevails. Personally I still prefer manual (e.g. pan shot) over the automatic tracking function provided by camera because the former choice gives me better control.
AF mode summary
I use Flexible spot AF mode extensively, that is my favorite mode. Unlike A7 system , where you can choose the size of the AF spot (L / M / S), the spot AF in A99ii lacks the flexibility so that shooter can’t choose the best size for various subject.
The Zone and Expanded Flexible spot are not very useful somehow. Instead of a precisely focused subject and sharp image, these two modes probably give you a barely focused area, it makes the image looks blur.
Overall speaking, the AF capability of A99ii meets my expectation however the design of AF mode is the Achilles heel of the entire system. That said, the shortcoming of Flexible spot AF can be overcame, I just need some time to get used to it and more practice.