Autofocus (AF) performance is one of the often quoted advantages of DSLRs over mirrorless cameras. Recent models like the Olympus OM-D E-M1 II and Fuji X-T2 have started to turn the tide, but the Sony A9 is designed to challenge the likes of the Nikon D5 and Canon 1DX Mark II which means it has an advanced hybrid focusing system with 693 AF points.
Sony A9 AF System: AF Modes
As you’d expect, the Sony A9 has Single and Continuous AF modes along with DMF (Direct Manual Focus) mode which allows you to tweak the focus manually. There’s also a collection of autofocus options which determine which AF points are available for focusing as follows:
Wide: The camera uses the whole area available for focusing with green frame marks (or small squares) indicating the point of focus. This is especially useful with subjects that move unpredictably.
Zone: In this mode you select a zone in which the target will appear, it’s more targeted than Wide area AF and is also useful with moving subjects.
Center: The A9 uses a rectangle at the centre of the sensor for focusing. It’s useful for the focus-and-recompose technique.
Flexible Spot: This mode is useful when you want to target a small area of the frame for focusing. The size of focus point can be switched between small, medium and large, but even large gives you a fairly precise area to work with. It’s handy for stationary subjects.
Expand Flexible Spot: This is similar to Flexible Spot but if the camera can’t focus on the single selected point it uses the surrounding points. It’s useful for when you want to target the focusing but the subject is a little tricky perhaps with low contrast.
Lock-on AF: In this is only available in continuous focus mode. It allows you set the starting focus point and once the shutter button is pressed half-way, the camera tracks the subject around the frame. The focus area can be set to small, medium or large. It’s useful with moving subjects that have a known starting position. If the active focusing area moves away from the the subject you need to reset the starting point.
Eye AF: This option option is useful for portraits and is hidden in the Camera Settings 2 section of the main menu under Custom Key (Shoot). Once you have assigned a control on the A9 to activate Eye AF you need to press and hold it while pressing the shutter release to take the shot.
Sony A9 AF System: AF performance
I’ve been using the Sony A9 AF system for the last week or so and it’s really impressed me. When I was photographing birds in flight on the Farne Islands I found that it was able to identify the subject with incredible speed and keep it sharp as subject distance changed. It quickly latched onto birds in flight and with a maximum continuous frame rate of 20fps (frames per second) I was provided with many sharp images.
In the past I’ve found that it’s best to restrict the focus area size as much as possible to get the subject in focus and keep it sharp. With the Sony A9 AF system, however, I’ve found that Wide setting, which uses all 693 focus points, works incredibly well. This is a significant advantage when you’re photographing a moving subject that could appear anywhere in the frame and move unpredictably.
Interestingly, when photographing my dog on a beach using Wide or Zone focusing in Continuous AF mode I found that if the dog was motionless the camera sometimes failed to identify the subject and focused a little closer to me than the dog. However, when my dog moved the A9 quickly snapped the lens into focus and kept him sharp as he raced towards me.
It also did a good job of focusing on his face, the closest part of him to me. If he turned away, his backside was the focus of attention.
Using Expand Flexible Spot and Lock-on AF mode also produced sharp images but there’s far greater onus on the photographer to frame the target correctly and my hit rate with birds in flight and my dog was much higher with Wide and Zone AF mode.
The downside to using Wide or Zone mode is that you leaving the focus point decision to the camera, but with green squares lighting up to indicate the point of focus (and a clear viewfinder) you can see where will be in focus and most of the time the A9 seems to get it right.
When I was photographing boxers in a ring at the Sony A9 launch event using Wide mode sometimes meant that the focus was on a boxing glove rather than a boxer, or a different boxer from the one I would’ve chosen, but the result was still usable.
There were a few occasions when the A9 wasn’t able to focus straight away on what seemed like a straightforward subject, but these were very few and far between. On the whole I’ve been extremely impressed with how it performs. It makes photographing difficult subjects easier than any other camera I’ve ever used.