AF-S (Nikon, Sony) or One-Shot AF (Canon) is a single-shot autofocus mode that locks focus when you half-press the shutter button, then stops adjusting. This mode is ideal for stationary subjects where you want to focus once, recompose, and shoot—ensuring the subject remains sharp even if you shift the frame after focusing.
How AF-S / One-Shot Works
When you half-press the shutter in AF-S/One-Shot mode, the camera activates autofocus using either phase detection or contrast detection (or both in hybrid systems). Once focus is achieved, the camera confirms acquisition—usually with a beep or indicator light—and locks focus at that distance. The lens stops moving. Even if you or your subject shifts slightly, focus remains fixed until you release the shutter button and start over.
This “focus and lock” behavior is fundamentally different from continuous AF (AF-C/AI Servo), which keeps adjusting focus as long as the shutter is half-pressed. AF-S is designed for static scenes: portraits, landscapes, still life, architecture, macro—any subject that isn’t moving unpredictably.
Focus-Recompose Technique
One of the most powerful uses of AF-S is the focus-recompose technique. Here’s how it works:
- Place your active AF point on your subject (e.g., a person’s eye).
- Half-press the shutter to lock focus and wait for the confirmation beep.
- While keeping the shutter half-pressed, recompose the shot to your desired framing (e.g., rule of thirds).
- Fully press the shutter to take the photo.
Focus remains locked at the original distance, even though you’ve changed the composition. This technique is especially useful when your camera’s AF points don’t cover the edges of the frame, or when you want creative control over the exact focus point and composition.
Practical Applications
Portraits: Focus on the subject’s nearest eye using a single AF point, lock focus, then recompose for a more dynamic composition. At wide apertures (f/1.4, f/1.8), this ensures the eye is tack-sharp even if you shift the frame slightly. For moving subjects, switch to AF-C.
Landscapes: Use AF-S to focus on a specific element—a foreground rock, the middle of a tree line—then recompose if needed. Alternatively, use manual focus with live view magnification for ultimate precision. For focus stacking, AF-S allows you to methodically step through focus points, locking each one before shooting.
Macro photography: At 1:1 magnification, depth of field is razor-thin. AF-S with contrast detection provides the precision needed to nail focus on a bee’s eye or a dewdrop. Use live view magnification to verify critical focus before shooting.
Studio and product photography: When your subject is stationary and lighting controlled, AF-S ensures repeatable, consistent focus across multiple frames. Lock focus once, then shoot variations without refocusing.
Limitations of AF-S / One-Shot
Moving subjects: If your subject moves after you lock focus, the image will be out of focus. For action, sports, wildlife, or children, use AF-C/AI Servo instead.
Focus-recompose errors: When using very wide apertures (f/1.4, f/1.2) and recomposing significantly, the focus plane can shift slightly due to the arc of your camera’s movement. For critical work, either use an AF point directly on your subject or focus manually in live view.
Shutter lock: In AF-S mode, many cameras won’t allow you to take a photo until focus is confirmed. If the lens hunts and can’t lock focus (low light, low contrast), you may be unable to shoot. Switch to manual focus or use AF-C, which allows shutter release even if focus isn’t confirmed.
Back-Button Focus and AF-S
Back-button focus is a powerful technique that pairs beautifully with AF-S. Instead of activating autofocus with the shutter button, you assign AF activation to a dedicated button on the back of the camera (usually AF-ON). Half-pressing the shutter no longer autofocuses—it only meters and fires the shutter.
With back-button focus, you press the AF-ON button to focus and lock, then release it. Focus stays locked until you press AF-ON again. This gives you ultimate control: you decide exactly when to focus, and the shutter becomes a simple “fire” button. You can shoot multiple frames at the same focus distance without the camera trying to refocus between shots.
Tips for Mastering AF-S / One-Shot
- Use a single AF point: For maximum precision, manually select a single AF point and place it exactly where you want focus (e.g., the eye). This is faster and more accurate than letting the camera choose from a zone or all points.
- Wait for confirmation: Don’t rush. Half-press the shutter and wait for the beep or indicator before recomposing. Premature recomposing can result in missed focus.
- Minimize recompose distance: The farther you recompose from the original focus point, the greater the risk of focus shift, especially at wide apertures. For extreme recomposing, consider manual focus.
- Use live view for critical focus: In studio or macro scenarios, switch to live view, magnify 5x or 10x, and use AF-S with contrast detection for pixel-level accuracy.
- Combine with focus limiters: On telephoto or macro lenses, set the focus limiter to reduce hunting and speed up AF-S acquisition in predictable shooting distances.
When to Use AF-S vs. AF-C
Use AF-S/One-Shot when:
- Your subject is stationary (portraits, landscapes, architecture)
- You want to use focus-recompose technique
- You’re working methodically (studio, macro, tripod-based work)
- You want the camera to refuse to shoot if focus isn’t confirmed (reduces accidental out-of-focus shots)
Use AF-C/AI Servo when:
- Your subject is moving (sports, wildlife, kids, pets)
- You need continuous tracking
- You want the freedom to shoot even if focus isn’t perfect (action scenes where a slightly soft shot is better than no shot)
Some cameras offer AF-A/AI Focus, an automatic mode that switches between AF-S and AF-C based on subject movement. While convenient for beginners, most pros prefer to manually select the appropriate mode for full control.
AF-S/One-Shot is the workhorse focus mode for most photography. Master the focus-recompose technique, and you’ll have precise control over focus and composition in any static scene. For everything that moves, switch to AF-C and let the camera’s tracking take over.