Single autofocus, labeled AF-S on many cameras and One Shot on others, is an autofocus mode in which the camera focuses once when the shutter button is half-pressed and then locks that focus distance for as long as the button stays held. In photography focus & autofocus terms, it is the mode designed for stationary subjects, in contrast to continuous autofocus, which keeps adjusting focus while the subject moves.
Because focus is locked, the photographer can focus and then recompose the frame without the camera searching again. Most cameras also apply focus priority in this mode, meaning the shutter will not fire until focus has been confirmed.
How single autofocus acquires and locks focus
When the shutter button is half-pressed or the AF-ON button is pressed, the camera evaluates the selected AF point or area using phase detection, contrast detection or a hybrid of both. The lens motor drives the focus group until the system confirms focus, typically within about 0.05 to 0.5 seconds depending on light, lens motor and subject contrast.
Once focus is confirmed, the camera signals it with a beep, a green dot or a highlighted AF frame, and the lens stops moving. From that moment, the focus distance stays fixed until the button is released, even if the subject or camera moves.
| Step | Camera action | Photographer’s cue |
|---|---|---|
| Half-press | AF system measures the selected area | AF point flashes or searches |
| Focus drive | Lens motor moves to the measured distance | Brief lens movement or sound |
| Confirmation | Focus is verified and locked | Beep, green dot or solid frame |
| Hold | Focus distance remains fixed | Recompose freely |
| Full press | Shutter fires at the locked distance | Image is captured |
Many cameras let the photographer change the default focus priority to release priority in a custom menu. With release priority, the shutter fires even if focus has not been confirmed, which avoids missed moments but accepts the risk of soft images. For deliberate single autofocus work, keeping focus priority is the safer default because it prevents unconfirmed exposures.
Names and behavior across camera systems
The concept is the same across brands, but the labels differ. Many systems call it AF-S or Single-shot AF, while Canon uses One Shot. Several cameras also offer an automatic hybrid mode that starts in single autofocus and switches to continuous autofocus if it detects motion.
| Mode | Common labels | Behavior |
|---|---|---|
| Single autofocus | AF-S, One Shot, S | Focuses once and locks |
| Continuous autofocus | AF-C, AI Servo, Servo AF, C | Keeps refocusing while active |
| Automatic switching mode | AF-A, AI Focus | Starts single, switches on motion |
| Direct manual focus | DMF, AF+MF | Single autofocus with manual touch-up |
| Manual focus | MF, M | No automatic focusing |
The label AF-S can also refer to a lens motor designation in one manufacturer’s lens names. In the context of focus modes it always means single autofocus, not a lens type.
Single autofocus compared with continuous autofocus
The essential difference is when focus stops changing. Single autofocus locks once; continuous autofocus predicts and follows subject motion, which is essential for sports and wildlife but can cause focus drift on static subjects when the system reacts to small movements.
| Aspect | Single autofocus | Continuous autofocus |
|---|---|---|
| Best subject type | Stationary or slow-moving | Moving toward or across the frame |
| Shutter release rule | Usually focus priority | Usually release priority |
| Recomposing | Focus stays locked | Focus follows the new frame center |
| Battery use | Lower, lens rests after lock | Higher, motor keeps working |
| Main risk | Missed focus if subject moves | Hunting or drifting on static scenes |
Many experienced photographers use back-button focus with continuous autofocus and simply release the AF-ON button to hold focus, which imitates single autofocus without switching modes. The dedicated single mode remains simpler and gives clear confirmation for deliberate, static work.
When single autofocus is the right choice
Single autofocus suits any situation where the subject distance does not change between focusing and capture. Typical uses include landscapes, architecture, product photography, posed portraits and street scenes where the photographer pre-focuses on a spot.
- Posed portraits: focus on the nearest eye, lock and fine-tune framing.
- Landscapes and architecture: focus at a chosen distance and keep it for the series.
- Product and still life: confirm focus on a precise point before each exposure.
- Low-light static scenes: focus once with the AF-assist light, then shoot without re-acquisition.
- Tripod work: lock focus, then switch to manual focus to prevent changes between frames.
Single autofocus is less suitable for children, pets, sports and moving vehicles. In those cases, a subject that moves even a few centimeters toward the camera between focus lock and exposure can fall outside the depth of field, especially with fast lenses and telephoto focal lengths, so continuous autofocus is the better choice.
Pitfalls of focus and recompose
The classic single autofocus technique is to focus with the center point and recompose. With wide apertures and close subjects, rotating the camera after locking moves the plane of focus, an error known as the cosine effect. At f/1.4 and a distance of about one meter, this shift can push an eye out of the very thin depth of field.
- Use an off-center AF point placed on the subject instead of recomposing at wide apertures.
- Refocus after any distance change, including when the subject leans forward.
- Avoid low-contrast targets such as plain walls, where the system may fail to lock.
- Check the confirmation signal rather than assuming focus was achieved.
- Disable the beep in quiet venues but keep the visual confirmation.
Modern cameras with eye detection reduce the need to recompose, because they can lock focus on an eye anywhere in the frame even in single autofocus.
Stripped to the essentials
Single autofocus means the camera focuses once and then stays put. You press the button halfway, the camera makes the subject sharp, and it holds that sharpness while you keep the button down.
It is like pointing at something and saying that is the spot. As long as the subject does not move closer or farther away, you can adjust the framing and still get a sharp picture.
Where it is applied
A real estate photographer shoots a furnished living room on a tripod at 16 mm and f/8. Using single autofocus, the photographer places a single AF point on a sofa cushion about three meters away, half-presses until the camera confirms focus, then switches the lens to manual focus so nothing changes during a five-frame exposure bracket.
Because the focus distance stays locked, all five bracketed frames align perfectly for HDR blending. In continuous autofocus, small refocusing steps could have shifted the plane of focus between frames. The final merged image is sharp from the foreground rug to the far window, and the session moves quickly from room to room.