The
advantages of AF-On with AF-C in Release priority
You're
always ready for action photography.
The "Focus, then Compose" technique can still be
easily used.
Switching to manual focus with telephoto lenses is easily
accomplished at any time by simply releasing the AF-On button
and manually turning the focusing ring.
-
Note: To use the "Focus, then Compose" process with
AF-On Only and AF-C focus mode, Release Priority (FPS Rate)
must be used. If the AF-C focus mode is set to Focus Priority,
then the shutter will not fire once the camera is shifted
for desired composition (since the area now in front of active
AF sensor would be out of focus).
Admittedly, it does take some time to get
adjusted to using the AF-On button. Initially there will be
some fumbling at times to locate the AF-On button with your
thumb. This problem is compounded by the fact that the vertical
release AF-On button is in a different (more vertical) position
compared to the horizontal release AF-ON button. With practice,
however, it will soon become second nature.
**Alternative
Solution: One can also use the "Focus, then Compose"
process in AF-C mode with Shutter Button activating AF (CSM
a5 in default setting). Simply press the AE-L/AF-L button
to lock AF and then recompose. To do the same when using the
vertical shutter release, you must use CSM a8 to reprogram
the vertical AF-On button to function as an AE-L/AF-L button.
This method works, but I prefer to completely separate AF
from shutter release by setting CSM a5 to AF-On only.
Some
photographers question the accuracy of AF-C for routine photography
since they find that the camera often continually adjusts
focus on a "stationary" subject. They consider this
a sign that the camera is "hunting" for the correct
focus. In actuality the camera is simply doing what it is
supposed to be doing—continually adjusting focus after
subject or camera movement. Often it is the camera that is
moving—slightly shifting the active sensor position
horizontally and/or vertically across a three-dimensional
subject. You can check this out easily for yourself by focusing
on a two-dimensional, high contrast subject (such as a brick
wall) with camera locked in position on a tripod. The camera
will focus quickly and accurately, without hunting, whether
in AF-S or AF-C mode.
Note:
In low light with low contrast subjects, the D2X can be slow
in acquiring focus. The focus indicator oscillations that
are occurring in this situation may actually be due to "hunting"
for correct focus rather than adjusting to subject/camera
movement. The result may be out of focus images. In these
situations, it may be best to use AF-S, which locks focus
once acquired, or to manually focus.
Other
photographers complain of a problem using the AF-On button
for AF acquisition when using telephoto lenses with VR. Since
the AF-On button does not activate vibration reduction, they
feel that VR "kicking in" as the shutter button
is depressed can blur images. I have not noticed this problem,
but I tend to partially depress the shutter button as I get
ready to take a photo, allowing VR to activate before fully
depressing the shutter button.
