D700 AF-ON button

[dspindle]

<p>I'm confused about the AF-ON button on the D700. If I assign AF to the AF-ON button only (not the shutter release) does the AF-ON button lock focus? In other words can I focus on my subject using the AF-ON button....let go......and then recompose and press the shutter release? Or do I need to hold down the AF-ON button while recomposing and pressing the shutter release? (I'm using Single Point AF)<br>

Thanks,<br>

Dave</p>

[al_derickson]

<p>It locks it in the sense that focusing is only working while the AF-ON button is pressed. When you release it the lens stays at whatever focus it was. It doesn't lock it in any of the modes where focus is kept on a moving subject.</p>

[joseph_smith3]

<p>Dave, it works as you described it in your sentence beginning "In other words..." It works the same in S or C. I use it all the time on my D 700. In AF-S, I focus with AF-ON pushed, then release it to lock the focus, then recompose, then trip the shutter at the right moment. For something like birds in flight, set AF-C, focus on the birds as they are moving by pressing down the AF-ON button, then trip the shutter when you want to capture continuous action.<br>

John Gerlach has a very good article on AF-ON at his web site. I suggest you look for it by Googling Gerlach back button focusing. That article convinced me to try it.<br>

Joe Smith</p>

[blumesan]

<p>The result of using the AF-ON button in <strong>AF-S</strong> mode might be other than what you expect. Yes, a <strong>push and release</strong> of the button does lock focus to the distance of the object under the selected focus point. However if you have set the AF-S priority selection (CSM a2) to the default (Focus Priority), when you reframe <em>the shutter will refuse to fire if the object under the selected focus point is no longer in focus</em>. This is true for the D700 and is what makes trap focus possible with this camera. The behavior of the D800 is different. </p>

<p>Further, if one wishes to lock focus and then reframe (such that the object under the focus point is no longer in focus), you must <strong>press and hold the AF-ON button</strong> to allow the shutter to fire.</p>

[hans_janssen]

<p>Why don't you try it?</p>

[dspindle]

<p>Thanks, everyone. Just what I needed. Your help is much appreciated!<br>

Hans......haven't received camera yet. Any day now! Was just reading up and getting ready.</p>

[kevin_beretta]

<p>Focus trapping is very useful if, for instance, you want to shoot runners coming around a track at the same point every time. Or models on a catwalk. You can manually focus somewhere in mid-air close to where you are positioned. Press the shutter when the runner gets closer. As he hits focus, the camer a will fire. You need to set the camera to only shoot when in focus and AF-ON set to only focus with AF-ON and not with the half-press on the shutter. Even easier with a remote. Put the camera on a tripod and press and hold the remote when the runner is close.</p>