ewelch
wrote:
AF-S is actually the type of lens that has the focusing motor in
the lens in Nikon nomenclature. For example, the D40 and D40X only
autofocus with AF-S lenses.
I'm fully aware of that: hence my "argh" exclamation at the overloading
of the term. Single-Servo-AF is also often called AF-S. Continuous-
Servo-AF is AF-C. We have two things that AF-S means. That
didn't have anything (much) to do with the question. AF-S pertaining
to lenses is different from AF-S pertaining to cameras. But one
can spell out the servo thing if people need cluing in--I guess.
Continuous mode is for photographing moving subjects (sports,
birds, cars, kids) where the subject will move out of the focus
plane while focus in the single mode would not follow.
In AF-Single, a moving subject is still tracked if was in motion when
the lock was made. AF-Continuous will catch motion that starts up
after the initial focus is made that wasn't there initially. It keeps
reapprising the situation. If you are using one of the 3/4 AF modes
that permit tracking to a different sensor than the initial one used,
then if the subject moves so far/fast that it can use another sensor,
it will. Focus tracking with AF-S works fine if you AF a moving subject.
With AF-C, if the subject isn't moving at when you first engage the
AF system, but then later starts moving, then that is also tracked.
Thus the single mode is for normal everyday shooting where you
don't need follow focus.
Have you noticed the difference in getting in-focus shots that are
extreme close-ups between AF-S and AF-C? Perhaps it's just me,
but I find I do better with AF-C. For example, the 105VR; use
that and get closer than I dunno, 1:4, 1:5 or so, and you're bobbing
around a fair bit. With AF-C, I get more keepers.
You lock the focus when you touch the
shutter release and then while it's locked you recompose and press
the shutter release the rest of the way to get the photo.
What does "lock the focus" even mean, really? How is this any
differerent than leaving your camera on AF-C, tapping your AF-On
button to focus once--or holding it to focus continuously until
you like it--then releasing your focusing button and recomposing,
then shooting? You can focus and recompose set to AF-C just as easily as set
to AF-S; more so, maybe.
It's kind
of the way you work with a Leica rangefinder. Focus with the spot
in the middle and then recompose. Obviously not the way to shoot
football. For example, with portraits it works way better than
continuous mode where the lens will hunt in and out looking for
better focus.
It does seem to, doesn't it? But the subject's eye isn't really moving,
is it? I use the 105VR for portraits a bit, and I don't keep the AF
system constantly engaged for that reason. But why would I have
to be in AF-S mode to do that? How is this any different that tapping
the AF-On, touching up the focus by hand if you want to and can
manage to see, then releasing the shutter?
Both serve their purpose and neither is a cure-all. It's not
either/or. And don't forget, manual focus works great too.
Great is overstatement. If I had to rely on my eye (which is 20/20)
I wouldn't get many, especially in low light. I've tried shooting
the Ai-S 105/2.5 at f/2.8 in indoor, nighttime lighting, and it is quite
tough to nail the eye. About the only time I override is for fence
shots where you're shooting through a grating, or for real macro
work (1:1 or thereabouts). Otherwise my idea of when it's in
good enough focus is often not what the green dot thinks.
I was
shooting a hummingbird the other day in a dense bush and if I had
relied on AF I would not have gotten any photos in focus. With
manual focus I got lots of photos of the little buggers gathering
nectar.
Why? Was the background tricking the AF system into being more
attractive than the birds? Were they too small for the get good
coverage of the AF sensors? Did you know where they were going
to be so you prefocused in the general vicinity and relied upon an
aperture that was small enough to include them?
I know I couldn't possibly focus fast enough and accurately enough
to follow hummingbirds in the general case. It would take a lot of
set-up and observation. Consider a 300mm lens at 30' away. At f/8,
you have something like a 1' depth of field of so. But if you were
closer than that, or with a wider aperture, it's worse. Half the subject
distance to 15' and open up a stop to f/5.6, and you now have a DoF
that's under 2". That's asking a lot for eyeballing--at least for me.
I wish otherwise, but that's just the way it is. With a 2" target zone
on a subject that small, I need any help I can get. Running AF-S
lenses in AF-C mode certainly helps. Hard to get it settle down though
on little targets, but it still does much better than I can.
It's pretty simple really when you consider the logic.
I'm afraid I'm not there yet then. I haven't figured out what AF-S
buys you over just tapping the AF-On key and letting go of it and
being in AF-C mode.
And if you operate that way, you stop cursing the AF selector lever,
because if it's AF-C, it doesn't flip off of its setting. I guess the people
using it set to S keep messing up. There's another thread where they
curse it a lot. This doesn't happen to me, because if you leave
it in AF-C mode, you all three without trouble. Grab the lens and
twist if you want to MF sometime or other. Hold the AF-On button
for continuous focusing. Tap it for one-time--and roll over to AF-L
if in focus priority not shutter prioirty. With the camera set to AF-C,
you get all those. With AF-S, well, you don't. There must be something
I'm not seeing about what makes AF-S a desirable lever setting.