Page 83 - (DK) Advanced Photography Guide

FO CUSING 81

CALIBRATING AF FOCUS LOCK

DSLR phase-detection AF is fast, but it can be imprecise, as With Single-shot AF selected, focus is locked as long as the
the lens sometimes focuses slightly behind the subject or shutter button is half-pressed. This lets you recompose and
slightly in front, known respectively as back and front shoot without the focus distance changing. This technique
focusing. Many DSLRs let you calibrate individual lenses is useful if you want to shoot an off-center subject that
to compensate for this shortcoming, and the details are would otherwise be outside the AF area. Locking focus
saved to the camera so that they may be applied whenever with Continuous AF is slightly more complicated.
that lens is attached. You can calibrate accurately by using Professional cameras and lenses often have a dedicated
a commercial distance scale that enables you to take focus lock button that pauses AF. Consumer cameras don’t
precise measurements and correct such errors. usually have such a button, but you can assign the task to a
customizable function button if your camera allows this.

AUTO

Auto (or AF-A) is a mix of Single-shot and Continuous AF.
If the subject is static, the camera will lock focus when the
shutter button is partially pressed down, as for Single-shot.
But if the subject then moves, the system will start tracking
the movement exactly as it does when using Continuous AF.
Although this sounds ideal, there’s often a very slight lag
before AF begins to track the subject. This pause can be
enough to miss the moment you wanted. If your subject
is likely to move, Continuous AF is a better option.

BEST FOR
FOCUS YOUR CAMERA
◾ ◾ Studio photography Set Single-shot AF and Single point selection (see
◾ ◾ Wildlife and macro subjects that are still but may move p.83) on your camera. Select the central AF point, then
move your camera so that it covers the subject. Press the
◾ ◾ Most portrait work
shutter button halfway to activate and lock the focus.

RECOMPOSE THE SHOT
▲ Auto AF is not generally the best mode for shooting wildlife. Keep the shutter button held down and move the
The exceptions are animals that are relatively tame and are camera to compose the shot correctly. Press down fully
behaving in a predictable way. on the shutter button to take the picture.

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