How to Autofocus in Live View and Movie Mode with a Nikon D5100
As with viewfinder photography, you can opt for autofocusing or manual focusing a Nikon D5100 during Live View shooting, assuming that your lens supports both. If you use the kit lens, set the lens switch to A for autofocusing. Follow the steps involved in choosing the autofocus settings and then actually setting focus:
Choose the Focus mode (AF-S or AF-F) and AF-Area mode.
You adjust both settings via the Quick Settings screen. The button that takes you to that screen is the Info Edit button. The camera restricts you to using the Face Priority AF-Area mode in the Auto and Auto Flash Off modes and Wide Area mode in the Miniature Effects mode.
If you set the Focus mode to AF-F, the autofocus system perks up and starts hunting for a focus point immediately.
Locate the focus frame in the Live View display.
The appearance of the frame depends on the AF-Area mode, as follows:
Wide Area and Normal Area: You see a red rectangular frame. (The figure shows the frame at the size it appears in Wide Area mode; it's smaller in Normal Area mode.)
Face Priority: If the camera locates faces, you see a yellow focus frame around each one. One frame sports corner brackets inside the frame. The brackets indicate the face that the camera will use to set focusing distance.
If you don’t see any yellow boxes but instead see a plain red frame, the camera can’t detect a face and will set focus as it would if you were using Wide Area mode.
Subject Tracking: A focusing frame appears.
In AF-F mode, the frame turns green when the object under the frame is in focus. The frame blinks any time focus is being reset.
Use the Multi Selector to position the focusing frame over your subject.
In Face Priority mode, you can use the Multi Selector to move the box with the double-yellow border, which indicates the final focusing point, from face to face in a group portrait. In the Wide Area and Normal Area modes, press OK to quickly move the focus point to the center of the frame.
In Subject Tracking AF-Area mode, press OK to initiate focus tracking.
If your subject moves, the focus frame moves with it. To stop tracking, press OK again. (You may need to take this step if your subject leaves the frame; press OK to stop tracking, reframe, and then press OK to start tracking again.)
In AF-S autofocus mode, press the shutter button halfway down to start autofocusing.
Wait for the focus frame to turn green.
What happens next depends on your Autofocus mode:
AF-S mode: You also hear a little beep (assuming you didn't disable the beep, which you can do via the Beep option, found on the Shooting/Display section of the Custom Setting menu). Focus is locked as long as you keep the shutter button pressed halfway.
AF-F mode: Focus will be adjusted if the subject moves. The focus frame turns back to red (or yellow or white) if focus is lost; when the frame turns green and stops blinking, focus has been achieved again. You can lock focus by pressing the shutter button halfway. In most cases, the camera will reset focus on your subject when you press the button even if the focus frame is already green.
(Optional) Press the Zoom In button to magnify the display to double-check focus.
Each press gives you a closer look at the subject.
As when you magnify an image when you’re viewing photos in playback mode, a small thumbnail appears in the corner of the screen, with the yellow highlight box indicating the area that’s currently being magnified. Press the Multi Selector to scroll the display if needed.
To reduce the magnification level, press the Zoom Out button. If you're not using Subject Tracking mode, you can also press OK to quickly return to normal magnification.