Choose the right AF mode

NPhoto - - Sharpen Up Your Slr Skills -

Ac­cu­rate fo­cus­ing is, of course, vi­tal for sharp pho­tos. The ma­jor­ity of cam­eras across the Nikon range of­fer the same three aut­o­fo­cus op­tions – sin­gle-servo AF, con­tin­u­ous-servo AF and auto-servo AF. Choose sin­gle-servo when the sub­ject is sta­tion­ary, as once the cam­era achieves fo­cus it stays locked at that dis­tance.

If the sub­ject moves closer or far­ther away af­ter fo­cus is locked then they’ll be blurred in the photo. If you want to track a mov­ing ob­ject, then con­tin­u­ous-servo is the AF mode of choice. Here, the cam­era never locks the fo­cus, con­stantly ad­just­ing the fo­cus dis­tance in re­sponse to move­ment de­tected by the ac­tive AF points. The down­side is that if your sub­ject be­comes ob­scured then the cam­era will po­ten­tially re­fo­cus else­where. Higher-end Nikon cam­eras let you fine-tune the sen­si­tiv­ity and speed of con­tin­u­ous servo to avoid this.

Auto-servo AF might sound like the per­fect com­pro­mise when you’re try­ing to work quickly. It ini­tially locks onto the sub­ject cov­ered by the fo­cus point but will then au­to­mat­i­cally switch to con­tin­u­ousservo AF to track the sub­ject when the fo­cus point dis­cerns a change in dis­tance. The drawback is that you’re re­ly­ing on the cam­era to make a judge­ment call on whether the sub­ject is mov­ing or not, and hav­ing to wait that split-sec­ond longer to trig­ger fo­cus track­ing might make the dif­fer­ence to get­ting the shot or not.

De­spite the Usain Bolt-style ac­cel­er­a­tion built into the likes of the D500 and D5, you can’t ex­pect the cam­era to reach top aut­o­fo­cus speed from a stand­ing start. If the sub­ject is small in the frame or lacks contrast for the AF sen­sors to ‘bite’ onto, then there’s also a risk that the cam­era will fo­cus the lens back and forth, hunt­ing for the sub­ject. But you can give your cam­era a fight­ing chance by pre-fo­cus­ing at roughly the dis­tance at which you an­tic­i­pate the ac­tion will take place. In some sit­u­a­tions, it may even be bet­ter to pre-fo­cus on an area and switch the lens to man­ual fo­cus to lock the set­ting in, as Andy ad­vises be­low…

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