I. CAMERA FEATURESAND OPERATION 11
Autofocusing Techniques:
Off-Center Focusing Pointsvs.
“FocusLock and
Recompose”
Fine-Tuning Your Camera
with Custom and
PersonalFunctions
Some mightthink that it’s a good idea to keep the shutter button half-pressed all the
time, butbattery life will be shortened significantly by that technique. The best balance
between power consumption and AFperformance is to anticipate picture-taking
opportunitiesand do not press the shutter button halfway until just a second or two
before pressing allthe way for the shot.
The 45-pointArea AF sensor covers a significant portion of the picture area, especially
with the originalEOS-1D and EOS-1D Mark II. However, many photographers never use
the off-center focusing points, preferring the old-fashioned method oflocking focus with
the center pointand then recomposing for the actual image. Before multi-point AF
cameraswere available, “Focus Lock and Recompose” (FLR) or manual focuswere the
onlychoices available. That’s no longer the case.
FLR issufficiently accurate for photographing distant subjects, but it can cause focusing
errors, especiallybackfocus, when photographing subjects within about 15 feet of the
camera. Thisis often the case during portraiture. For optimum focusing performance
with close subjects, we recommend avoiding the FLR technique. Instead, use an off-
center focusing pointor focus manually.
EOS-1 classdigital SLRs are equipped with an extensive variety of Custom Functions
(C.Fn) and PersonalFunctions (P.Fn) that allow photographersto tailor many aspects of
camera operation according to personalpreferences. Although there are minor
differencesin the quantity and variety of C.Fns and P.Fns according to individualcamera
models, mostof them are consistent across the product line. For the purposes of this
document, we willconcentrate on C.Fns and P.Fnsthat affect AF performance with EOS-1
classdigital SLRs.
Custom Function 4allows the photographer to control which button on the camera is
used to startor stop AF. It also ties in with AE Lock when the camera is setto an AE
mode.
•C.Fn 4-0 (the default setting) starts AF and AE when the shutter button is pressed
halfway. AELocks automatically upon focus completion when the camera is set for the
combination ofOne-Shot AF and Evaluative Metering. With other AF modes or metering
patterns, AELock can be initiated manually by pressing the AE Lockbutton on the
backof the camera.
•C.Fn 4-1 switches AF start to the AE Lock button, and starts AE Lockin AE modes with
anymetering pattern when the shutter button is pressed halfway. This mode is
popular with sportsphotographers and some photojournalists, especially those who
originallylearned photography with manual focus SLRs. It works particularly well with
USM lensesthat have distance scales, because such lenses feature full-time manual
focusing even when the lensis set for AF. With C.Fn 4-1, the photographer can
manuallyfocus such a lens at any time, and then start or stop AF independently from