Started Jan 25, 2013 | Discussions thread
chlamchowder Senior Member • Posts: 2,083
Re: AF-ON button behavior

With all due respect I don't think you have really learned how the current cameras operate when you have AF activation set to AF-ON only.

Set the camera AF activation to AF-ON Only. Set priority selection to focus priority. Set it this way for both AF-C and AF-S mode. Now point the camera at something that is out of focus. Do not press the AF-ON button. Now press the shutter button. The camera takes a photo.

Yes, that's exactly what happens. If there's no AF operation going on (i.e., AF-ON button not being held down), the camera just releases when you hit the shutter.

It doesn't matter whether you have the camera in AF-C or AF-S mode. There is no difference between focus or release priority behavior. You lose ALL focus priority logic. Who cares about AS-S lens manual AF override at this point?

There is still a difference when the AF-ON button is held down. In either AF-S or AF-C mode, the shutter won't release until the AF drive gets to where the camera wants it to be.

With focus priority set, try completely defocusing the lens. Then press AF-ON, and hit the shutter release immediately after, before the lens can reach the desired focus position. You'll notice a lot more shutter delay, because the camera won't release the shutter until it can focus the lens. In release priority, you can fire the shutter while the lens is still trying to get there (resulting in a heavily defocused image, assuming you're fast enough to beat the lens AF drive).

When shooting a burst in AF-C while holding down AF-ON, you'll also notice that the frame rate 'hiccups' when the subject is coming in so fast that the lens has trouble keeping up, or minor FPS slowdowns when the subject makes quick movement changes that aren't anticipated by the camera. In release priority, the camera just blasts off at full speed regardless of whether the AF system is actually keeping up.

At least that's how the D600 operates when the back AF-L/AE-L button is set to AF-ON, which removes AF operation from the shutter button. They might have made it so that there's absolutely no difference between focus and release priority on the D800 regardless of whether the AF-ON button is pressed, but I don't know - I only played with one for a few minutes, and I didn't test that.

If you want AF-S lens manual AF override you can have exactly the same capability with the old camera behavior in release priority mode.

Yes, but then you won't get the camera to slow down the framerate to keep up with unpredictable, fast moving subjects. You also won't be able to mash AF-ON and the shutter button, and have the camera fire as soon as it gets things in focus.

Perhaps I'm missing something. I'm certainly open to hearing where I am going wrong on my understanding of the new behavior.

Hopefully I explained the difference in a way that isn't completely convoluted, and hopefully the D800 and D4 actually behave in the same way as the D600, and don't just completely ignore focus/release priority altogether. Anyways, it'd definitely be nice to have a setting governing how the camera interprets release/focus priority, like having two focus priority options ("strict" focus priority that allows for trap focus, and "loose" focus priority that can only lock the shutter while the lens AF drive is running).

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