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Why Use AF-ON Button?

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But it seems to me that you are effectively disabling the ability to get focus confirmation when you use this setting, specifically with small DoF's, say on a 1.8 50mm.

On the D200, the AF-S is essentially a non-entity when you use the AF-ON button. If you push AF-ON, then re-frame to spot meter on another subject, you are essentially ruining the focus you had on the first subject anyway, so you might as well use AE-L on the spot first, then focus on the subject -- I would rather have a slightly out of exposure image than a slightly out of focus image.

Also, in AF-S, you now have to use your thumb to not only select the focus point -- which I'm always doing to try to stay one step ahead of my subjects -- but now you double up the job of that wonderful opposing thumb, and make it do focus as well.

I hope you are following what I am saying.

Basically, I see a significant degradation in the ability to get sharp focus images unless I use f/8 or higher on AF-C with high shutter speeds with AF-ON -- in that situation, this would make sense; otherwise, using the AF-ON button essentially means you are going to be using AF-C only. The advantage you get is that you can continue to hold the AF-ON button and shoot away regardless of whether you are actually in sharp focus or not.

I suppose I could be missing some setting that would make it so AF-S works after you release the AF-ON button and move to another subject, or that you could move the frame and still claim to actually have true focus on the original subject, but I doubt that the laws of lens and DoF physics can be bent -- even by Nikon. Or, I could just be really bad at it, and I need more practice.

Please, change my mind on this, I'm not an expert, and I'm always open to new ways of utilizing the technology. But I just can't see it working well unless you have sufficient DoF and high shutter speeds.

--
http://dlensphoto.blogspot.com/
 
photorover said:
But it seems to me that you are effectively disabling the ability to
get focus confirmation when you use this setting, specifically with
small DoF's, say on a 1.8 50mm.

On the D200, the AF-S is essentially a non-entity when you use the
AF-ON button. If you push AF-ON, then re-frame to spot meter on
another subject, you are essentially ruining the focus you had on the
first subject anyway, so you might as well use AE-L on the spot
first, then focus on the subject -- I would rather have a slightly
out of exposure image than a slightly out of focus image.

Also, in AF-S, you now have to use your thumb to not only select the
focus point -- which I'm always doing to try to stay one step ahead
of my subjects -- but now you double up the job of that wonderful
opposing thumb, and make it do focus as well.

I hope you are following what I am saying.

Basically, I see a significant degradation in the ability to get
sharp focus images unless I use f/8 or higher on AF-C with high
shutter speeds with AF-ON -- in that situation, this would make
sense; otherwise, using the AF-ON button essentially means you are
going to be using AF-C only. The advantage you get is that you can
continue to hold the AF-ON button and shoot away regardless of
whether you are actually in sharp focus or not.

I suppose I could be missing some setting that would make it so AF-S
works after you release the AF-ON button and move to another subject,
or that you could move the frame and still claim to actually have
true focus on the original subject, but I doubt that the laws of lens
and DoF physics can be bent -- even by Nikon. Or, I could just be
really bad at it, and I need more practice.

Please, change my mind on this, I'm not an expert, and I'm always
open to new ways of utilizing the technology. But I just can't see it
working well unless you have sufficient DoF and high shutter speeds.
Click to expand...
I'm not sure I'm following what you're saying. Are you saying that using the AF-ON if you focus and then reframe you have lost focus if you have a very skinny DOF?

If that is what you're saying, how does using AF-S and a half-press make matters better?

Just trying to understand the thinking.

Leroy
 
You are following.

It makes it better in that I get my metering first, then recompose to focus, then get the focus confirmation "beep" (if you have it turned on) and are able to shoot in a small DoF with as accurate a focus as possible.

I posted my "P.S. " to the wrong post above, I meant to ad it to my own post to clarify how I have learned to use the AF-ON button. I do not allow the AF-ON to be the only way the camera focuses. I use the AF-ON button when in AF-C mode, and I use the standard shutter release in AF-S mode.

--
http://dlensphoto.blogspot.com/
 
photorover said:
You are following.

It makes it better in that I get my metering first, then recompose to
focus, then get the focus confirmation "beep" (if you have it turned
on) and are able to shoot in a small DoF with as accurate a focus as
possible.
Click to expand...
Ah. So you're metering, then holding the AE-L, recomposing, half-press for focus, then full-press for shutter release. Which means the problem is you don't have two thumbs, one for the AE-L and one for the AF-ON. ;-)

I wish there was a way to press AE-L and have it hold exposure until release but I don't know of a way.

The implication is that you're using A or S mode. I don't come across this problem because I use M mode so my exposure is always locked.

So yes if you do that very often (AE-L and recompose), AF-ON might not be your cup of tea.

Leroy
 
lwiley said:
photorover said:
You are following.

It makes it better in that I get my metering first, then recompose to
focus, then get the focus confirmation "beep" (if you have it turned
on) and are able to shoot in a small DoF with as accurate a focus as
possible.
Click to expand...
Ah. So you're metering, then holding the AE-L, recomposing,
half-press for focus, then full-press for shutter release. Which
means the problem is you don't have two thumbs, one for the AE-L and
one for the AF-ON. ;-)

I wish there was a way to press AE-L and have it hold exposure until
release but I don't know of a way.

The implication is that you're using A or S mode. I don't come
across this problem because I use M mode so my exposure is always
locked.

So yes if you do that very often (AE-L and recompose), AF-ON might
not be your cup of tea.
Click to expand...
On the D300 you can use F6 to make the AE-L hold exposure - set it to 'AE lock (hold)'. Then you can press and release the AE-L and it will hold your exposure. It keeps the exposure held until you press AE-L again or turn the camera off.

So you do not need two thumbs to use AF-ON even if you set your exposure first in A or S mode.

I don't know about the focus beep because I don't have it turned on but you always have the green dot in the viewfinder.

Leroy
 
Not sure it has been mentioned yet.

AF-On comes into handy when shooting landscape/cityscapes and using Braketing Bursts.

I first focus with AF-On, recompose, shoot the bracketing burst (e.g. using the fn button if you use the D300) and be sure all shots retain the same focus - otherwise each shot would have refocused on the new target after recomposing. In D300 I assign this combination to a custom-bank.

Again always when shooting static stuff I find it useful to focus and forget in order to concentrate on composing the shot then. But this is more of a psycological reason...

I find it less interesting for tracking objects where AF-C + Dynamic area make the game just using the shutter release button.

A more advanced thought: I generally prefer to use AF-on to decouple the moment of focus from the shutter release: first press AF-On, then recompose and take pict. Others in the forum don't mind using AF-On in combination with shutter release (both pressed at the very same moment), but then if you also need Fn or Preview for another function you must become an octopus to manage your camera... :)

g
 
Since I started using it, I can't imagine ever going back to focusing with the shutter-release button (except when I give the camera to someone else to take a picture).
--
Ron
CP5700, D70, D300
http://www.pbase.com/ronhrl

Every man has a right to his opinion, but no man has a right to be wrong in his facts. --Bernard Baruch
 
OK but let's say you see kids running around and need to take pictures of them pretty quickly. If my camera is in AF-S mode, then I would have to stop what I'm doing, flip the switch to AF-C. But during this time, I lost my opportunity. I can't tell you how many times I missed a shot or the picture was blurry because I was in AF-S mode. Yes, the focus confirmation beep helps in letting you know if the picture is in focus or not, but doesn't help if you need to be in AF-C mode regardless for that shot where you need to track movement.

In essence, using AF-ON exclusively with AF-ON button with AF-C, I am practically taking the advantage of both worlds (AF-C and AF-S). Therefore, I am ready regardless if my subject is static or moving.
photorover said:
I do see a great value in learning to use the AF-ON button in
conjunction with the AF-C function, but in leaving the setting in
it's default state so that I can also use the focus lock confirmation
"beep" I get when using AF-S.

--
http://dlensphoto.blogspot.com/
Click to expand...
--
-Dan
 
Another trick you can use to lock focus without using the AF-ON button is:

Find subject and focus using the shutter release button
Release shutter button
use your left thumb to switch the AF-S, AF-C, Manual lever to manual.
press the shutter button to take the picture.

This works for stationary subjects only.
 
I've been on again off again with this button but I've been using it steadily now for a few months. Only problem I find is that since I'm a right eye dominant shooter, my thumb gets in the way of my glasses sometimes and causes smears on my glasses.
--
Fiat Lux
 
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