Back button AF: One shot or AI Servo?
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RonMJ
Registered: Feb 24, 2012
Total Posts: 53
Country: United States

I'm going to try back button AF on my 5D2. Which AF mode to you use with BBAF, and why? One shot, AI Servo, or AI Focus? Thanks!



tgawczynski
Registered: Mar 24, 2006
Total Posts: 82
Country: United States

I didn't think it really mattered... I use it all the time on AI Servo. Maybe I've been doing it wrong. haha



RobDickinson
Registered: Sep 25, 2009
Total Posts: 3578
Country: New Zealand

I have mine on AI servo and tap it if I want 'one shot'.



msalvetti
Registered: Dec 20, 2003
Total Posts: 2901
Country: United States

I use back button in all AF modes. I think once you start using it, you won't stop.

I don't find a back button tap in AI Servo as reliable as One Shot, so if One Shot is appropriate, I'll switch to it from AI Servo. On my 7D, I can also set the DOF button to toggle between one AF mode and another, but that only works as long as you hold it down, and often that's awkward.

Mark



EB-1
Registered: Jan 09, 2003
Total Posts: 23206
Country: United States

Servo.

EBH



schlotz
Registered: Jan 06, 2002
Total Posts: 2946
Country: United States

Ron, bbaf is a setting to separate the af function from the shutter button so that half depressing the shutter does NOT engage the af function. Instead the af is controlled by the * button. It matters not the mode you have the camera in, one shot, ai servo or ai focus. The * button will control the af regardless.



G-Gore
Registered: Sep 18, 2005
Total Posts: 421
Country: United States

Both modes, but in dark conditions, when I have flash on, you need to switch to One Shot to be able to use assist light from the flash.



stargazer78
Registered: Jan 19, 2009
Total Posts: 383
Country: United States

RobDickinson wrote:
I have mine on AI servo and tap it if I want 'one shot'.




This is not a good idea.

A.I. Servo is optimized for tracking moving subjects, and therefore sacrifices precision for faster focus acquisition. One-Shot does not make that same compromise, and therefore has stricter parameters for focus accuracy.




garyvot
Registered: Apr 02, 2003
Total Posts: 3140
Country: United States

One Shot. Unless I'm shooting something moving, then AI Servo.



skibum5
Registered: Jan 21, 2005
Total Posts: 16898
Country: United States

RonMJ wrote:
I'm going to try back button AF on my 5D2. Which AF mode to you use with BBAF, and why? One shot, AI Servo, or AI Focus? Thanks!



I mostly don't use. I find the front button much more natural. When not using a big lens with an AF stop button for certain circumstances you may need to use it at times, bit when not needed I keep it off.
SOme like it, some don't. Despite forum talk, not all sports shooters on the sidelines actually use it, while some do, plenty don't (other than, as I said, during certain particular circumstances when using certain lenses).



PhilDrinkwater
Registered: Feb 24, 2010
Total Posts: 1958
Country: United Kingdom

schlotz wrote:
Ron, bbaf is a setting to separate the af function from the shutter button so that half depressing the shutter does NOT engage the af function. Instead the af is controlled by the * button. It matters not the mode you have the camera in, one shot, ai servo or ai focus. The * button will control the af regardless.


Definitely. It's nothing to do with the focus mode.

To answer the question - I use both. If I need accuracy I use one shot. If I need to track movement I use AI servo. I personally wouldn't use AI servo unless I was tracking movement - you will lose some accuracy for using it.



PhilDrinkwater
Registered: Feb 24, 2010
Total Posts: 1958
Country: United Kingdom

stargazer78 wrote:
RobDickinson wrote:
I have mine on AI servo and tap it if I want 'one shot'.


This is not a good idea.

A.I. Servo is optimized for tracking moving subjects, and therefore sacrifices precision for faster focus acquisition. One-Shot does not make that same compromise, and therefore has stricter parameters for focus accuracy.




Agreed. It's not a good idea but I know a lot of people do it.

Really a person needs to make a decision which they use more - if they need tracking focus most of the time, it might make sense to do this for the occasional shot which would ideally be One Shot.



RobDickinson
Registered: Sep 25, 2009
Total Posts: 3578
Country: New Zealand

I do switch to singe sometimes in the rare instance its more appropriate. Considering I mostly shoot landscapes anyhow..



dgdg
Registered: Jul 20, 2011
Total Posts: 2962
Country: United States

I certainly found AI servo was poor for static objects with the 5DII, but with the 5DIII it may be different, perhaps just as good if one sets AF priority?



diverhank
Registered: Aug 07, 2012
Total Posts: 226
Country: United States

PhilDrinkwater wrote:

This is not a good idea.

A.I. Servo is optimized for tracking moving subjects, and therefore sacrifices precision for faster focus acquisition. One-Shot does not make that same compromise, and therefore has stricter parameters for focus accuracy.




In theory, it sounds very logical but in practice, I think it's a myth. Imho, AI Servo is just as good. Take a look at the great BIF shots on this forum and tell me that the focus could have been better...I beg to disagree. They are shot using AI Servo, correct? And they are perfect, correct?



badlydrawnboy
Registered: Mar 19, 2006
Total Posts: 1856
Country: United States

Both. I have the depth of field button set to toggle back and forth between One Shot and AI Servo. Then I have Custom Function modes set up as follows:

C1: A-priority (@f/1.2 or whatever widest aperture of mounted lens is) and One Shot focus. This is for portraits of mostly stationary subjects for precision focusing. However, if the subject starts moving, I just hold down the DOF preview button and AI Servo engages.

C2: A-priority (@f/2.8) and AI Servo. More for moving subjects I want to isolate from the background. But if I want more precision in focus, I just hold down the DOF preview button for One Shot.



dgdg
Registered: Jul 20, 2011
Total Posts: 2962
Country: United States

Badly,

What are you using for autofocus points? When you toggle between focus modes with the DOF button, you'll not be able to easily toggle different AF areas. The reason is, the DOF button is the only button that can alternate between the current AF point and the registered AF point. Once you set that DOF, your out of luck.

The one issue I am working on is I would like 61 point AF for servo, and single point for One shot. Have not found a quick way to toggle this. Maybe I'll just need to set it for center point with surrounding assist for both.



badlydrawnboy
Registered: Mar 19, 2006
Total Posts: 1856
Country: United States

On C1 I have it set to single focus point, top center. On C2 I have it set to expanded focus point (not sure of the terminology, but where each of the squares around a selected focus point are used/highlighted). I've set up C3 to track moving subjects across the frame, and am using the 61-points in AI Servo on that.

I just select the focus point set-up I want using the focus point button on the back of the camera in each custom function mode, and choose "save all settings".



Pixel Perfect
Registered: Aug 16, 2004
Total Posts: 19928
Country: Australia

badlydrawnboy wrote:
On C1 I have it set to single focus point, top center. On C2 I have it set to expanded focus point (not sure of the terminology, but where each of the squares around a selected focus point are used/highlighted). I've set up C3 to track moving subjects across the frame, and am using the 61-points in AI Servo on that.

I just select the focus point set-up I want using the focus point button on the back of the camera in each custom function mode, and choose "save all settings".


This was the only way I could see that would do what dgdg wants. Setup separate C# settings.



ifxbonz
Registered: Mar 02, 2004
Total Posts: 1737
Country: United States

stargazer78 wrote:
RobDickinson wrote:
I have mine on AI servo and tap it if I want 'one shot'.




This is not a good idea.

A.I. Servo is optimized for tracking moving subjects, and therefore sacrifices precision for faster focus acquisition. One-Shot does not make that same compromise, and therefore has stricter parameters for focus accuracy.



I would bet you that 85% of full time sports shooters including me use BB AF in servo mode. It sacrifices nothing! and I would argue its delivers more accurately focused images than with the shutter button alone.

I shoot everything BB AF.

Andy



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