Trap Autofocus - Nikon D300 Complete Manual

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turning on Focus point using Display mode on the

PLAYBACK menu and then navigating to the page that

shows that information during image playback.

There's good news, too:

Focusing can occur over a large area. Only the D2 series

can claim to cover as wide an area of the image frame as

the D300, and those earlier cameras had gaps in the

middle of their coverage that the D300 doesn't have. The

D300 can focus on subjects far more off-center than can

its predecessor, the D200.

Low light performance covers a wider area. The fifteen

crossed sensors in the middle of the autofocus sensor

array cover a wider area than those in the D200 or any

other camera Nikon has made. Even the D2 series, which

had nine very large crossed sensors scattered over the

frame didn't quite cover as much contiguous area for low-

light performance as the D300.

Focusing is integrated with metering. The reason why Auto

Area is so good at recognizing people in a frame has to do

with the integration with the metering sensor, which

provides the color information that tells the autofocus

system where skin tones occur in the frame. Likewise, if

you select 51point 3D tracking, the meter provides pattern

recognition information to the autofocus sensors, which

helps them determine where in the scene your subject has

One important thing to note: in terms of user control, the

Autofocus Area settings range from total (bottom selection on

the control switch: Single Point) to none (top selection on the

control switch: Auto). If you find that you don't have enough

control of the sensor area used for focusing, try using the

Autofocus Area mode setting immediately below the one

you're using!

Trap Autofocus

If you've used a Nikon film SLR, you may have encountered a

special autofocus mode called "trap autofocus." On some

Thom Hogan's Complete Guide to the Nikon D300