Sony's New a6400 Camera Focuses in a Blink—Here's What That Means

In January 2019, Sony released a new mirrorless camera called the a6400. The headline feature: it can lock focus on a subject in just 0.02 seconds—roughly the time it takes to blink. The camera also includes face and eye detection that follows moving subjects, a 24-megapixel sensor, and a faster processor than its older cousins.

For people new to camera gear, the speed sounds impressive. Let's break down what it actually does and who benefits most.

What the Camera Can Do

The sensor and lens mounting. The a6400 uses an APS-C sensor, which is a physical size of image chip that falls between smartphone cameras and professional full-frame cameras. It's common in enthusiast and professional photography. Sony's E-mount system means you can attach many different lenses to this body.

The autofocus system. Traditional autofocus is straightforward: you point the camera at a subject, press the shutter button halfway, and the camera adjusts the lens until the image is sharp. The a6400's autofocus is remarkable because it does this extremely quickly—in 0.02 seconds—across 425 different points on the sensor.

More usefully, the camera includes two features that most casual photographers don't encounter in everyday use:

• Real-time Eye AF: The camera detects a person's eye and keeps it in focus, even if the person moves their head, turns slightly, or walks across the frame.
• Real-time Tracking: The camera remembers a subject's color and pattern, then follows it around the frame automatically, switching between wide-area and narrow focus modes as needed.

These features sound like magic. In practice, they save photographers from constantly adjusting focus while recording video or shooting bursts of photos.

Video and display. The camera can record 4K video at 24 or 30 frames per second. Its electronic viewfinder shows you a live preview on a small screen inside the camera (2.36 million dots of resolution), and the back LCD screen tilts but doesn't fully rotate.

The processor handles the heavy computational lifting behind the scenes—tracking algorithms, eye detection, and continuous autofocus calculations all happen in real time.

Who Should Care

The a6400 is built for people whose subjects move around: wedding photographers, sports shooters, videographers, and content creators making social media videos. If you're photographing a soccer game or filming a friend dancing, the camera's tracking keeps the action sharp without constant manual adjustment.

The real-time features matter less for other kinds of shooting. A landscape photographer taking pictures of mountains, a studio photographer working with stationary subjects, or someone photographing food won't gain much from super-fast eye tracking.

There's a practical trade-off. All that autofocus computation drains the battery quickly. Sony rates this camera at roughly 410 photos per charge under standard test conditions. If you're shooting all day, you'll need spare batteries. The tilting screen is also a limitation—it doesn't rotate fully, which makes some video setups more awkward.

The Bigger Picture

Sony didn't invent autofocus tracking overnight. The company has been gradually improving focus speeds since it introduced the first a6000 back in 2014. Each new model has gotten a bit faster and covered more of the sensor. The a6400 is the latest step in that progression.

Looking at the competitive landscape, Fujifilm and Canon both make mirrorless cameras in this size and price range. Their autofocus systems work differently—Fujifilm emphasizes color science and film simulations; Canon focuses on smooth video autofocus—but none is dramatically slower in real-world use. The differences matter mainly to specialists.

In this author's view, the a6400 represents a meaningful but not revolutionary leap. The eye-tracking and subject-following features are genuinely useful for the people who need them, yet they're increasingly becoming standard across the industry rather than a Sony-only advantage. What's worth noting is that Sony is pushing this kind of intelligent autofocus into more affordable bodies, making it available to photographers who can't afford the pricier models.

The a6400 is an incremental step forward, not a fundamental shift. If you're shopping for a camera and you shoot a lot of moving subjects, it's worth testing. If your photography style doesn't involve constant motion, other factors—build quality, battery life, or the specific lenses you already own—may matter more.