You have chosen where the camera should focus. Now there is one more decision: should the camera focus once and stop, or keep adjusting focus as long as you hold the button? For a still portrait the answer is different from a running dog. This is the choice between single-shot and continuous autofocus, and getting it right makes a big difference with anything that moves.
Two autofocus modes
- Single-shot autofocus: when you half-press the shutter button, the camera focuses once and then locks. As long as you hold the half-press, focus stays at that distance, even if the subject moves.
- Continuous autofocus: while you hold the half-press, the camera keeps measuring and adjusting focus, following the subject as its distance changes.
| Brand | Single-shot | Continuous | Automatic switching |
|---|---|---|---|
| Canon | One-Shot AF | AI Servo AF (Servo AF) | AI Focus AF (some models) |
| Nikon | AF-S (Single-servo) | AF-C (Continuous-servo) | AF-A (some models) |
| Sony, Fujifilm and others | AF-S / Single | AF-C / Continuous | AF-A (some models) |
Some cameras also have an automatic mode that switches between the two if it detects movement. It is handy for beginners, but it can be unpredictable, so most photographers choose one mode themselves.
Why continuous AF matters for moving subjects
Imagine a child running toward you. In single-shot mode, the camera focuses when you half-press, say at 5 metres. A second later, when you take the photo, the child is at 3 metres. The plane of focus, which you learned about in what is focus, is still at 5 metres, so the child is blurred.
In continuous mode, the camera keeps moving the focus as the child comes closer. Many cameras even predict where the subject will be at the moment the shutter opens. The child stays sharp.
| Single-shot (AF-S / One-Shot) | Continuous (AF-C / AI Servo) | |
|---|---|---|
| What it does | Focuses once, then locks | Keeps adjusting while you hold the button |
| Best for | Still subjects: portraits, products, landscapes, buildings | Moving subjects: sports, children, pets, wildlife, vehicles |
| Focus and recompose | Works, because focus stays locked | Does not work; focus follows whatever is under the point |
| Will it take a photo before focus is found? | Usually no: it waits for focus | Usually yes: it may fire even if focus is not perfect |
Remember:That last row matters. In single-shot mode, many cameras will not take the picture until focus is confirmed. In continuous mode, many cameras take the photo when you press, even if focus is still adjusting, so you do not miss the moment. Most cameras let you change this priority in the menu.
Continuous AF works with AF area modes
Continuous autofocus is where AF area modes like zone and tracking, from selecting AF areas and focus points, really work. Continuous AF keeps adjusting the distance; tracking keeps moving the focus point across the frame to stay on the subject. Together, with subject detection, modern cameras can follow a bird across the sky or a player across a field.
Tip:Use continuous AF with burst shooting (continuous drive mode) for action. Several frames in a row give you more chances of a perfect moment, and the camera keeps refocusing between frames.
Back-button focus
Normally, the shutter button does two jobs: a half-press focuses, a full press takes the photo. Many photographers separate these jobs. They set the camera so that a button on the back, often marked AF-ON, does the focusing, and the shutter button only takes the photo. This is called back-button focus.
| Shutter-button focus (default) | Back-button focus | |
|---|---|---|
| To focus | Half-press the shutter | Press the back button with your thumb |
| To keep a focus locked | Hold the half-press | Simply let go of the back button |
| Switching between still and moving subjects | Change the AF mode in the menu | Leave it in continuous: hold the back button to track, release it to lock |
| Learning curve | None | Takes some practice |
The big advantage is that you can leave the camera in continuous AF all the time. Holding the back button tracks a moving subject; letting go locks focus for a still one. You do not need back-button focus to take sharp photos, but many sports, wildlife and wedding photographers like it. You can set it up with the button customization you learned in basic camera customization.
A simple way to choose
- Will the subject's distance change before or while I shoot? If no, use single-shot. If yes, use continuous.
- Is the subject moving across the frame? Add zone or tracking area mode.
- Is it fast and unpredictable? Add burst shooting and subject detection if available.
Common mistakes
- Single-shot AF for moving subjects: focus locks on where the subject was, not where it is.
- Focus and recompose in continuous AF: the camera refocuses on whatever is under the point after you move.
- Half-pressing too early with moving subjects in single-shot: the longer you wait, the further the subject moves from the locked distance.
- Turning on back-button focus before an important shoot without practice: missed photos while your thumb learns the new habit.
How professionals work
Many professionals who photograph people and action leave their cameras in continuous AF with subject detection most of the time, often using back-button focus, so the camera is ready for both still and sudden moments. Landscape, product and architecture photographers usually stay in single-shot, or focus manually, because their subjects never move. In every case, they choose the mode based on one question: will the distance change?
Practical examples
A dog running to its owner
- Situation
- In single-shot AF, every photo of the running dog shows sharp grass behind it.
- What to do
- You switch to continuous AF with zone area and burst shooting.
- Why it works
- The dog's distance changes every moment; continuous AF follows it.
- Result
- Most frames show the dog sharp, mid-stride, ears flying.
A product on a table
- Situation
- You photograph a watch for an online shop and want to compose with the watch off-centre.
- What to do
- You use single-shot AF, focus on the watch face, hold the half-press and recompose.
- Why it works
- The watch does not move, so locking focus is reliable.
- Result
- A sharp watch face in a balanced composition.
Key points
- Single-shot AF focuses once and locks; continuous AF keeps adjusting while you hold the button.
- Canon calls them One-Shot and AI Servo; Nikon, Sony and others use AF-S and AF-C.
- Use single-shot for still subjects and continuous for anything whose distance changes.
- Continuous AF works best with zone or tracking areas, subject detection and burst shooting.
- Back-button focus separates focusing from taking the photo, so one mode can handle both.
Frequently asked questions
What is the difference between AF-S and AF-C?
What is AI Servo on Canon cameras?
Can I use focus and recompose in continuous AF?
What is back-button focus?
Conclusion
Single-shot autofocus is for subjects that stay still; continuous autofocus is for subjects whose distance changes. Combine continuous AF with the right area mode and burst shooting for action, and consider back-button focus once the basics are comfortable. Next, you will learn when and how to focus by hand.
Finished reading? Track your progress through Focus and depth of field.