With an all-new and world's first stacked CMOS full-frame sensor, the Sony a9 looks to be a force to be reckoned with. Check out our first look video to get yourself up to speed on Sony's latest sports shooter.

We got some additional time with the camera, and captured some through-the-viewfinder video showing the new AF system in action:

We start off showing AF tracking by using the camera's 'Lock-On: Flexible Spot M' mode. This does a seemingly improved job of sticking to our intended (initial) subject. Sony claims much improved subject tracking; and our initial impressions confirm this, though Lock-on still experiences a delay in initially locking on to your subject.

We then take a critical look at AF joystick usage. The joystick allows a function to be assigned to an inward press (it's Center AF-S by default). We also look at the newly added ability to tie a specific AF mode (with or without AF activation) to custom buttons, which is potentially game changing when it comes to quickly adapting to changing scenarios. Unfortunately, you can only ever switch to one other AF mode using this particular function, but thankfully there's a workaround (keep reading, below this video). Quickly switching back-and-forth between two AF area modes is one of the things we truly enjoy and use when shooting high-end Canon/Nikon DSLRs.

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But wait, there's more. We found a workaround to assign many more AF modes to other buttons - and instantly override many other camera settings - via 'Recall custom hold'. This function combines some of the best customizations both Canon and Nikon DSLRs provide, and there are 3 such banks you can set up and assign to most custom buttons. We explore this in-depth in our video below: