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AF-ON Focusing Method, D700 & D800 compared.

Mike Blume , Jan 31, 2013; 12:55 a.m.

I count myself among a group of Nikon shooters who routinely decouple autofocus initiation from the shutter button and assign it to the AF-ON button only. We find this shooting method provides certain efficiencies which have been well described in a recent post here on Pnet. I would guess that those of us who prefer this shooting method are in the minority of all Nikon users. Many are totally unaware of this method and many others have given it a trial and found it did not suit their needs. Be assured I am not here to proselytize but merely to provide information to those who may find it useful.

When this shooting method is employed it is important to note certain differences in the behavior of the D800 camera and other Nikon dslrs released prior to that camera. These differences have been described (and disparaged) in several threads on this site and numerous other photography sites. However the descriptions I have found are generally fragmented and often incomplete with the result that I have not seen a fully parsed summary of the results. This post is submitted in an effort to provide such a summary.

The following is a comparison of the D700 & D800 used in AF-ON shooting mode.
Settings and operations common to both cameras are:

  • Lens: Any Nikkor AF lens. For my tests I used the Nikkor 24-70/2.8, AFS ED
    • AF-S Priority Selection: FOCUS. AF-C Priority Selection RELEASE; (default values). See exceptions noted below.
    • AF Activation set to OF-ON button ONLY.
    • AF Area mode set to SINGLE POINT.
    • Select focus point.
    • Focus lens with the AF-ON button.
    • Reframe the subject such that the object under the initially selected focus point is clearly out of focus. This is the meaning assigned to all following instances of “reframe” or “reframing”.
    • .

*********************************************************************************

D700:
1. AF-S Mode.
1.1. Acquire focus by press & release of AF-ON button. After reframing the shutter release will not fire the shutter. If the shutter release remains pressed the shutter will fire only if and when some object enters the area of the initially selected focus point. This is the routine method of trap focus with the D700.

1.2. Acquire focus by pressing the AF-ON button and keep button pressed. Focus remains locked while reframing and the lens does not refocus (initially set focus distance remains unchanged). The shutter release will fire the shutter. This is the common method of focus/lock focus/reframe & shoot.

2. AF-C Mode:
2.1. Acquire focus by press & release of AF-ON button: Focus remains locked while reframing and the lens does not refocus (initially set focus distance remains unchanged). The shutter release will fire the shutter. An alternative method of focus/lock focus/reframe & shoot.

2.2. Acquire focus by pressing the AF-ON button and keep button pressed. While reframing the autofocus remains active causing the lens to refocus on whatever object falls under the initially selected focus point. The shutter release will fire the shutter with no delay.

2.3. When AF-C Priority Selection is set to FOCUS (non default): Acquire focus by press & release of AF-ON button. After reframing the shutter release will not fire the shutter. If the shutter release remains pressed the shutter will fire only if and when some object enters the area of the initially selected focus point. This is an alternative method of trap focus with the D700. Note that it is identical to the behavior in AF-S mode (1.1 above).

********************************************************************************

D800:

3. AF-S Mode:
3.1. Acquire focus by a press & release of the AF-ON button: After reframing the shutter release will fire the shutter. Focus remains locked while reframing and the lens does not refocus (initially set focus distance remains unchanged). Essentially identical to the behavior of D700 described in 1.2 above, focus/lock-focus/reframe & shoot.

3.2. Acquire focus by pressing the AF-ON button and keep button pressed: After reframing the results are identical to 3.1 above. Note that in spite of the fact that AF remains engaged, the lens does not refocus.

4. AF-C Mode:
4.1. Acquire focus by a press & release of the AF-ON button: Identical to behavior in AF-S Mode, as described in 3.1 and 3.2 above.

4.2. Acquire focus by pressing the AF-ON button and keep button pressed: While reframing AF remains active causing the lens to refocus on whatever object falls under the initially selected focus point. The shutter release will fire the shutter.

4.3. Setting the AF-C Priority Selection to FOCUS (non default) causes no change in the behavior as described in 4.1 and 4.2 above (with the possible exception in conditions 4.2 that there may be a very brief delay in shutter firing until focus is reacquired).


REMARKS:

D700 users note: You can leave the camera set to AF-C mode for all shooting. The only exception being when you require trap focus you must switch to AF-S mode. Alternatively you can change the AF-C Priority Selection to FOCUS (involves menu selection and thus more awkward).

D800 users note: You can also leave the camera “permanently” set to AF-C mode with no penalty in functionality. The three alternative shooting methods described in 3.1, 3.2 and 4.1 above all produce an identical outcome. More the pity that the change introduced with the D800 provided two redundant shooting methods at the cost of disabling the ability to focus trap.

Responses


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Georges Pelpel , Jan 31, 2013; 01:27 a.m.

Thanks for this detailed explanation. What about VR?
I understand that with the D800 VR will be activated by the AF-ON button. Is VR deactivated if the AF-ON button is released and when the shutter is pressed.
Is it necessary to keep the AF-ON button pressed in order to keep VR on?

Francisco Disilvestro , Jan 31, 2013; 02:00 a.m.

Is it necessary to keep the AF-ON button pressed in order to keep VR on?

No, the VR will be activated either by the AF-ON or the shutter is half pressed

One note about the D800, if you select autofocus activation by AF-ON, it will work in "Release priority" for both AF-S and AF-C, regardless of whatever you configured. The shutter will fire even if you never pressed the AF-ON button

Ilkka Nissila , Jan 31, 2013; 03:46 a.m.

Francisco, that is not quite correct. With the D800, if you select focus priority, AF-ON AF activation, and AF-C, and then press and hold the AF-ON slightly ahead of the shutter release button, the famera will focus and then take the shot. If you set release priority, it'll take the shot immediately after the shutter button has been pressed, before focus has been achieved.

If you press the shutter release slightly before AF-ON, or if you don't press AF-ON at all, the shot will be taken in either mode immediately, as far as I can determine. This is what has been altered from the D3/D700 generation; in focus priority the older cameras would not take the shot at all if there was nothing in focus under the active AF sensors.

Francisco Disilvestro , Jan 31, 2013; 07:11 a.m.

Ilkka, You're absolutely right. Thanks for pointing that out.

Mike Blume , Jan 31, 2013; 04:17 p.m.

Yes, Francisco. Ilkka is absolutely right. He has simply restated what I wrote in my initial post. It's all there if you read it carefully.

As for VR, since I don't own a VR lens I cannot give a reliable answer.

Francisco Disilvestro , Jan 31, 2013; 08:21 p.m.

Hi Mike,

The only thing I did not see in your post is that the D800 will take the shot even if you don't press the AF-ON at all, in any of the possible modes.

Mike Blume , Jan 31, 2013; 11:12 p.m.

Hi Francisco,
Another interesting quirk of the D800 is that, when set to Focus Priority in either mode, the only circumstance where the shutter will refuse to fire is when one attempts to focus on a blank wall or in light too dim to allow focus. Not that this observation is of any value in practice, but such is the case.

Andrew Garrard , Feb 01, 2013; 07:54 a.m.

Thanks for the summary, Mike, though I'm not sure I'd have left the trap focus difference as an apparent afterthought!

I think Ilkka (?) was previously making the point that there is a minor distinction between AF-S and AF-C modes. With AF-S, the camera will automatically stop trying to acquire focus once an initial focus has been acquired; with AF-C it will continue for as long as it's being asked to autofocus (this is the obvious distinction, not the minor one...) Using AF-S on a moving subject, you can be assured that the lens at some point locked on the subject when the lens stops focussing. With AF-C, it's hard to tell whether the lens is moving because it's trying to track the moving subject, or because it simply hasn't reached focus yet (or is totally failing to do so). When trying to focus on a small garden bird swaying in the breeze, this distinction has been important: I can arrange enough depth of field to cover branch sway, but knowing whether I've locked on the bird at all is useful - hence, especially in a hurry, I can't just press and release AF-On in AF-C and hope it's done the right thing. I appreciate that the distinction is minor, but I've used it.

If we're being authoritative, is it worth mentioning the behaviour with chipped manual-focus lenses? My understanding, and I've not tried it (though it makes sense logically), is that the camera will pay attention to focus priority if it thinks it's trying to autofocus the lens. Therefore a manual focus lens chipped to look like an autofocus will trick a D800 - and everything else - into performing trap focus. Obviously it doesn't matter whether you're using AF-On or the shutter button to "focus" in this case.

Mike Blume , Feb 01, 2013; 06:48 p.m.

Andrew,
I left the trap focus issue as a remark only because I was resisting the temptation to further edtorialize on this subject. You know my views. :(

It's hard to comment on what you have written since it isn't clear to which camera you are referring.

With the D800 there is essentially no difference in behavior between AF-S and AF-C modes when one uses the technique described at sec. 4.1. In AF-C mode the added functionality is described in sec. 4.2 and is obviously the preferred technique when trying to capture a moving bird. The change in behavior when one switches to FOCUS priority is stated in sec. 4.3. This will ensure that your bird is in focus before the shutter releases.

As for the D700, at default settings one must use AF-S to achieve trap focus. Otherwise anything that can be done in AF-S mode can be duplicated in AF-C.

PS I just happen to own one of the better chipped MF lenses available, Zeiss ZF.2 100/2.0. When I get a chance I will see how it behaves.


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