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"Back Button" AF

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I've seen "Back Button" autofocus mentioned and used a lot in tutorial videos - especially for shooting sports and wildlife. I think I get it - program one of the back buttons to be the AF trigger and to lock that in as long as you hold the button (or toggle the button? not clear on that either).

What I'm having a hard time figuring is out how exactly to set this up on my #Alpha 9 (a9) - what is this function called in the menu so I can assign it to a custom button?

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Hi Bengineer,

Yes, it is true that you can customize many of the buttons on Sony cameras.  The full frame 35mm cameras are the largest of the bodies in our lineup and therefore have more space for more buttons.  The early models of our cameras came with a button labeled AF/MF.  Later models came with a button labeled AF-ON, (Some people customized the AF/MF or AF-ON Button for other functions). The AF/MF button does function essentially as either a switch that can be rotated for either autofocus or/ Manual Focus.  Can be customized for either hold or toggle in the customization menu. If it’s customized for “HOLD” then it will focus if the button is held in. If it is customized to “TOGGLE” then you would press it to initiate focus and then press again to not focus.  Or if the switch is set to “MANUAL FOCUS” you would press shutter release to focus but then when you press the button in on the AF/MF Switch you would be able to focus manually by rotating the focus ring on the lens.  If this button is customized to toggle then you would press once to enter manual focus and press again to exit manual focus.

You have an a9 (ILCE-9) so you don’t need to worry about this.  The AF-ON button is simply a press to initiate focus. If you wanted to go into manual focus many of the lenses (But not all) have a switch that allows either AF (Auto focus) or MF (Manual Focus).  Also, the lower part of the dial to the left of finder (Focus Mode) can be set to either AF-S, AF-C, DMF or MF (Manual Focus).

For anyone else reading about this and you want to research and learn more about your camera or customizing please read my post “Where do I find more information on my camera"

By the way: If you are wondering why I keep referring to our cameras models as ILCE- model number.  That’s the internal Sony model name of your camera.  ILCE stands for “Inter-changeable Lens Camera E-Mount”.  If you have a lens from Sony that typically, (but not always) starts with SEL2470GM2 that “SEL” stands for “Sony E-Mount Lens”.

In the deeper menu system Sony does not label as “Custom Button”.  The call it “Custom Key”. Newer models of cameras do have a dedicated AF-ON Button, used for back button focus, (ILCE-7C, ILCE-7M3, ILCE-7M4, ILCE-7RM3, ILCE-7RM4, ILCE-7SM3, ILCE-9, ILCE-9M2, ILCE-1). Of course, the APS-C sensor cameras from Sony like the a6000 series of cameras also offers the ability to customize buttons as well.  But since the bodies are smaller you have less buttons to customize.

The newer cameras mentioned above that already have the AF-ON Button do not have to customize anything.  Some of the buttons on the camera already come pre-customized from the factory. Some of the pre-customized buttons are labeled, some are not labeled.  The AF-ON button is labeled and is pre-customized to perform autofocus.  You press the button and hold in while focusing.  Depending on your focus mode, (on the ILCE-9 camera it is the lower of two stacked dials to the left of the viewfinder, Standing from behind the camera), either AF-S (Single Shot AF) or AF-C (Continuous AF). This AF-ON Button will behave differently.  With AF-S you place your focus point on the stationary, non-moving subject. Press your AF-On button in and the camera will calculate the focus distance from the image sensor to the placement of focus are on the subject, (Focus area is the C2 button preconfigured from the factory. Focus area can also be found on the function menu by pressing the FN button to right side of LCD). Focus Area can also be found in the deeper menu as well.  Anyway… using AF-S calculates the focus distance but should you the photographer or the subject step forward or back, (thus changing your distance to the camera) you would need to take your finger off the AF-ON button, repress so the camera can re-calculate the distance from image sensor to subject again.  While if you change the focus mode from AF-S to AF-C the a9 will continuously calculate focus 60 times per second. So, if your subject or you move even just the slightest amount the camera will adjust.

Now, why would you want to use back button autofocus?  Well, when you press the focus button the camera takes a tiny fraction of a second to calculate the distance.  So, if you are using the shutter release half press you are calculating the distance and a full press fires the shutter.  By using the AF-ON button the camera has pre-performed the calculation already and has focus on the subject already. So, when you press the shutter, you don’t have to wait for any of this to happen.  The focus work is already completed.  It just speeds things up fractionally.  One important thing to note is not only does the AF-ON button come pre-configured and customized to perform Autofocus but the shutter release button is also configured to perform autofocus with a half press as well.  For those folks that are going to use AF-ON exclusively you might consider turning off the focus option on the shutter release. On the alpha-9 (ILCE-9) you would press the menu button to left of viewfinder, go to tab 1, (Maroon color with a white camera and a number 1), Go to Page 6 5th line down “AF w/shutter” and turn off. This will disable the focus feature from the shutter release. You would then only be able to focus using the AF-AN Button.  Of course, first decide if this is how you prefer to do your focusing.

If you have other buttons you would like to customize on the alpha 9 (ILCE-9) you can do so by pressing menu, go to Tab camera 2 (purple), go to page 9 and see “Custom Key”.  Yes, there are three custom Key lines.  The one with the little graphic of a mountain is to customize the buttons when in still photo mode, (Program, Aperture Priority, Shutter Priority, Manual).  The Custom Key with the film strip and sprocket holes is for customizing the same buttons but with functions that are more specific to video.  So, when you change your mode dial from one of the still settings to the little icon with the same graphic icon, (film strip with sprocket holes) you are now in the video mode and when you press the same buttons, they can have a customization different than what you had for stills. So for instance in video, you might want a feature liking Picture Profile, Audio or Zebra Striping).  You can have quick access to those by simply customizing these buttons for video. The third line down is Play Back Custom Key and has the graphic of the universal play arrow that we are all familiar with from using CD’s, DVD’s, Cassette Tapes VCR (I’m dating myself). You can learn more about custom key here for the ILCE-9:

Hope that answers your question on the Back Button Focus.

Thank You


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  • Solution

It requires only one change in the menu to accomplish this.  No biggie.  You have to remove the AF from activating from the shutter release button.  The AF-ON button is already active on the cameras right out of the box.  the menu you are looking for is in the 1st set on page 5.  Look for "AF w/ Shutter" and turn it OFF.  T22i9852E84F91B37BCE.thumb.jpg.6a05f620d1a96fe5847711afffef41de.jpghat's it!

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  • 1 month later...

@pm-r thanks for the concise reply - exactly what I needed. Just got back from my first weekend shooting "back button" and I really picked it up quick. It really made a difference on some things that were really challenging for me - like when my subject is going between obstacles and I need to re-lock on to the horses and not the gates. Definitely a lot more 'keeper' from this weekend than before!


#Alpha 9 (a9) #FE 100-400mm F4.5-5.6 GM OSS 1/2000 | f9 | ISO 400

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I find it unnecessary for these cameras, honestly... but thats just me. I love the snappy AF of the a9/a9ii/a1 and the tracking is great (although I rarely use it)--- I live in ZONE literally most of the time-- my subjects arent slow and usually have a bunch of things to distract around them532i75F06AE039B0DBC1.thumb.jpg.ed2231e1aba264b692ee2a812cb6264d.jpg

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Hey Ben, on my Sony a7RIV and my Sony a1, go into Operation Customize > Custom Key Setting and apply it to the button of your choice. What you want to set for that button is: AF/MF Selector Hold (this is the key). Now when you push this button it acts as a toggle to go from AF to MF - you do not have to push and hold. Leave your lens switch to AF and your Dial on the camera to MF. Simple and it works. Let me know if you have any issues... BTW - you can either leave your main shutter button on or off on your camera - really doesn't matter...

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