The following is an excerpt from The Fujifilm X-T5: 134 X-Pert Tips to Get the Most Out of Your Camera by Rico Pfirstinger.
AF-S or AF-C?
Your Fuji X-T5 features two basic Auto Focus modes that can be selected with the focus mode selector at the front of the camera:
■ AF-S (AF Single) is meant for stationary subjects. When you half-press the shutter button, the camera will focus on the object covered by the active AF frame and lock the distance (as long as you keep the shutter button half-pressed). You can either fully press the shutter button to take the shot, or you can take your finger off the shutter release and try again.
■ AF-C (AF Continuous) is meant for moving subjects, especially those that move toward or away from the camera. When you half-press the shutter button, the camera starts focusing on the object covered by the active AF frame and continuously adjusts the distance to the moving object while you keep the shutter button half-pressed.
While AF-C focuses using the set working aperture, AF-S can open the aperture beyond the working aperture to improve the AF performance in poor light. This also improves the focusing accuracy due to the reduced depth of field caused by the wide-open aperture.
When shooting with AF-C in poor light, it helps to keep the aperture wide open.
Single Point AF vs. Zone AF vs. Wide/Tracking AF
AF/MF SETTING > AF MODE lets you choose between SINGLE POINT, ZONE, or WIDE/TRACKING autofocus. The X-T5 also offer an ALL option, which lets you seamlessly select one of the three Auto Focus modes simply by changing the size of the focus frame or zone. You should definitely set your camera to ALL.
Single Point
■ Single Point AF mode is my recommended AF setting for most applications. In this mode, you can manually select one of up to 425 available focus frames. Try to avoid old habits like using only the center frame in concert with the focus-and-recompose [60] technique. It’s better to first compose the shot and then select a suitable AF frame that covers the part of the image you want to be in perfect focus. This helps you avoid focus errors that invariably occur when you pan the focus plane. Such focus errors may be irrelevant with long focal lengths and small aperture openings (larger depth of field) but focus errors can be quite unpleasant with wide-angle lenses, a wide aperture opening (small DOF), and in situations with a short distance between the camera and the subject. Single Point AF can be used in concert with both AF-S and AF-C.
Shooting with minimal depth of field, you can’t afford to use a focus and recompose habit because it would quickly lead to soft results that appear out of focus. Instead, compose the shot, and then focus using a single focus frame that covers the part of the image that is supposed to be in focus.
Zone AF
■ You can think of Zone AF as an extension of Single Point AF. Basically, an AF zone is a particularly large AF frame that consists of a matrix of smaller AF points. Zones are available in sizes that cover 3 x 3, 5 x 5, or 7 x 7 out of a total of 117 AF points. Like Single Point AF frames, AF zones can be moved around within the image area. Since they are larger than focus frames, AF zones make it easier to focus on moving subjects. In Zone AF mode, the camera will usually start looking for something to focus on in the center (crosshairs) of the selected zone and will then expand its search toward the edges of the zone until it finds a target. Like Single Point AF, Zone AF works in concert with either AF-S or AF-C.
Wide/Tracking AF
■ When you combine Wide/Tracking AF mode with AF-S, you get Wide AF mode. The camera scans the entire image frame and automatically selects several focus frames. It’s a bit like rolling dice, since the camera is simply looking for areas it can easily focus on. It doesn’t know what’s important in a scene. This changes when Wide/Tracking is used in concert with AF-C: this results in Tracking AF which offers real 3D tracking of moving objects; that is, objects that not only move toward or away from the camera, but also left, right, up, and down within the image frame. To track such an object, select Wide/Tracking and AF-C and pick one of the available AF points. To start the tracking process, make sure the selected point covers the moving object you want to track. Half-press the shutter button to start the tracking process. While you keep the shutter button half-pressed, the camera will automatically follow the selected subject as it moves across the image area.
Selecting an AF frame or AF zone
The X-T5 allows you to use the focus stick or the touchscreen to select a focus frame or zone. Make sure that the focus stick is configured as described in the previous tip.
Focus Stick
■ Pressing the focus stick opens the FOCUS AREA screen, where you can move around the focus frame or focus zone by tilting the stick in any direction. You can change the size of the frame or zone by turning the front or rear command dials. In AF mode ALL, doing so also changes the AF mode (Single Point, Zone, Wide/Tracking). In the FOCUS AREA screen, pressing the rear command dial resets the size of the zone or frame to their default values. Pressing DISP/BACK centers the position of the AF frame or zone.
■ You can also directly move the focus frame or zone around simply by tilting the focus stick without pressing it first. This is the easiest way to adjust the position of the focus frame. However, to have additional options like changing the size of the frames, you must first press the focus stick to get to the actual FOCUS AREA screen.
Pressing the focus stick opens the FOCUS AREA screen, where you can select a focus frame or AF Zone and change their sizes. Using the convenient AF mode ALL, changing the size cycles through AF modes Single Point AF (A), Zone AF (B), and Wide/Tracking AF (C).
Touchscreen
You can also use the touchscreen to change the position of a focus frame or zone. Make sure the touchscreen-AF interface is set to AREA mode, and then tap anywhere on the screen to select an AF area or zone.
You can even use the touchscreen like a trackpad to change the position of the focus frame or zone when you are looking through the electronic viewfinder (EVF). You can select the active trackpad area with SET UP > BUTTON/DIAL SETTING > TOUCH SCREEN SETTING > EVF TOUCH SCREEN AREA SETTING.
Of course, for all of this to work, the touchscreen must have been enabled in the first place, so make sure that SET UP > BUTTON/DIAL SETTING > TOUCH SCREEN SETTING > (camera symbol) TOUCH SCREEN SETTING is set to ON.
Choosing a suitable AF frame or AF zone size
The X-T5 offers 117 or 425 different AF frames in Single Point AF, and each frame comes in six sizes. You can change the size of an AF frame by pressing the focus stick and turning one of the command dials left or right to decrease or increase the frame size.
AF frame size affects the efficiency of CDAF and PDAF. A basic rule to follow is: Make your AF frame as large as possible and as small as necessary.
This is why:
■ With a larger AF frame size, the camera has more to work with and a better chance to find contrast in a target, especially when the light conditions aren’t optimal. There’s also a better chance the camera will be able to use the faster PDAF method. When PDAF isn’t possible, the camera will fall back to the slower CDAF.
■ With a smaller AF frame size, the autofocus becomes more accurate. A small AF frame gives you better control over exactly what the camera is focusing on. Avoid AF frame sizes that are larger than the part of your image that needs to be in focus. For example, if your AF frame is larger than the head of the person you are focusing on, there’s a chance that the camera will instead focus on the background behind them, especially if that background contains a lot of contrast.
To get tiny parts of an image in perfect focus, it’s best to choose a small AF frame size.
In a similar fashion, you can change the size of AF zones by pressing the focus stick and then turning the command dial left or right. You have a choice of three AF zone sizes: 3 x 3 (default), 5 x 5, or 7 x 7 out of 117 frames.
Since we can regard AF zones as very large AF frames, the same rules apply. Larger zones are more convenient, and they potentially offer a faster AF response, but they are also potentially less accurate than smaller zones.