AF-ON (Canon) - The AF-ON button allows you to trigger auto focus independently of the shutter release 'half-press'. Note that you can re-program the exact function of the AF-ON button through Custom Functions menu.


 (Canon)(AE/FE Lock) - Press to trigger automatic exposure and lock the exposure for the next shot; hold the button to lock the exposure for more than one shot. When an external flash is mounted, press to trigger flash exposure lock (via a pre-flash).


AE-L/AF-L (Nikon) - (Auto Exposure/Auto Focus Lock) - Pressing this button locks the current exposure and focus, they remain locked for as long as you hold the button even if you press or release the shutter release button.)

One Shot
(focus lock on half-press) / AI Focus (locks but monitors movement) / AI Servo (continuous predictive focus)

* AI Focus mode initially locks just like One Shot mode but monitors the focused subject.  If the subject moves it will automatically switch to an AI Servo operation.




AF-Area Mode (enabled thru menu) – Single Point, Dynamic Area, Auto Area, 3D Tracking


Auto-focus mode (AF Button)
AF-A (Auto select; switches between AF-S and AF-C automatically)
AF-S (Single-servo AF. Focuses once, then locks AF for you to recompose and shoot)
AF-C (Continuous-Servo AF.  Keeps focusing as the subject moves.)       



Back Button Focus on a Nikon D7000, etc.

1.) Assign the AE-L, AF-L button to AF-On. Menu - Custom Setting Menu - (pencil).
2.) Controls - Select F5 “Assign AE-L/AF-L button.” Select “AF-On.”
3.) Custom Setting Menu - Autofocus - Select A1 “AF-C priority selection” Select “release.”
4.) Set AF-S priority selection to “release” mode.


Back Button Focus on a Nikon D3100, D3200, etc.

1. Menu - Set Up menu (wrench) - Buttons

2. AE-L/AF-L button

3. Select AF-ON


Back Button Focus on Canon Cameras:


Go To Menu - Custom Functions -  Shutter/AE Lock Button"



EOS Rebel T3: C.Fn 7 (option 1 or 3)
EOS Rebel T3i: C.Fn 9 (option 1 or 3)
EOS 50D: C.Fn IV-1 (option 2 or 3)
EOS 60D: C.Fn IV-1 (option 1, 2, 3, or 4)
EOS 7D: C.Fn IV-1 (Custom Controls — Shutter, AF-ON, AEL buttons)
EOS 5D Mark II: C.Fn IV-1 (option 2 or 3)
EOS-1Ds Mark III: C.Fn IV-1 (option 2 or 3)
EOS-1D Mark IV: C.Fn IV-1 (option 2 or 3)



  Explanations of On-Screen Options (taken from Canon Learning Center )

0: Metering + AF start (note: there’s no slash here)

Factory-default setting. You activate camera’s meter and AF by pressing shutter button half-way down. Rear AF-ON button also does same if it’s pressed, so you don’t get the benefits of removing AF activation from the shutter button when this option is set.

1: Metering + AF start / AF stop

AF is still at shutter button. Pressing the rear button will actually LOCK the focus; potentially useful if you shoot a lot of moving subjects in AI Servo AF and prefer to activate AF with a conventional half-press of shutter button. Focus is unlocked by removing thumb from back-button.

2: Metering start / Meter + AF start
Back-button AF activation. Shutter button no longer activates AF, but of course fires the shutter. Metering is continuously updated — if you shoot a sequence of pictures, the camera takes a fresh meter reading for each one. There’s no locking of exposure, unless you separately press the AE Lock button (this last item is not possible on some EOS models).

3: AE Lock / Metering + AF start
Back-button AF activation. Difference between this setting and option 2 directly above is that when you press the shutter button half-way, your exposure is locked and won’t change until you pull your finger off the button entirely. Thus, if you shoot a sequence of pictures in any auto exposure mode, the exposure setting used for the first shot is used for each subsequent shot. Can be useful if you were using back-button AF to easily lock focus and shoot a series of portraits, where you wouldn’t expect lighting to change.

4: Metering + AF start / Disable
Similar to setting “0” above, but now, the camera’s rear AF-ON button is disabled. AF activation is at the shutter button. Convenient if you’re worried about accidentally pressing the back-button and don’t want to use back-button AF.

Carl P. Stillitano – Instructor
CPS Photography • 520 Broadway • Pitcairn , PA   15140
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