BBF, AF and AI Servo

[stevet1]

I just got into back button focus, and I like it a lot. It's a lot quicker, I think, but I have a question.

I haven't had a chance to experiment with moving subjects yet, so I'm not sure of something.

If I am in AI Servo mode, do I keep my finger on the BBF button as I follow the subject, or should I keep my finger off the button and let the AI Servo take care of things?

If I keep my finger on the BBF button, are the autofocing and the AI Servo working at cross purposes?

Does BBF work best in single shot mode?

If I understand it, AI Servo works best when the subject maintains the same distance, but what if you have somebody running let's say a zigzag pattern, moving either toward you, or away from you?

How should I handle that?

Thanks,

Steve Thomas

 

[weepete]

if you take your finger off the focus button your camera won't focus. So if you are wanting to track your subject using AF you need to keep the button depressed. There is a technique that uses tapping on the focus button to attain focus quickly and right before a shutter release, but in general you'll want to keep it pressed.

AF and AI servo don't work at cross purposes so thats fine, AI servo just tells your camera to constantly focus using the AF points.

BBF works best with AI servo IMO, as you can manually lock the focus by taking your finger off the focus button, though sometimes it's useful to have the AF point illumination on and that's only avalible in one shot.

There are a few modes of autofocus (dependant on your camera model), mine has one for subjects that are changing direction erraticaly. Often you can fine tune the AF further, make the tracking fast or slow, give priority to shutter release of focus etc

 

[zombiesniper]

Everything stated above is bang on. The one question about AI servo and zigzagging subject. AI servo will track all subjects. Crossing subjects. Closing subjects, Still subjects.
What camera do you have? Some have a couple of AF fine tuning functions while others have dozens of tuning functions.

 

[stevet1]

I just got into back button focus, and I like it a lot. It's a lot quicker, I think, but I have a question.

I haven't had a chance to experiment with moving subjects yet, so I'm not sure of something.

If I am in AI Servo mode, do I keep my finger on the BBF button as I follow the subject, or should I keep my finger off the button and let the AI Servo take care of things?

Steve Thomas

I have done some reading in the meantime, and I guess I've found my answer.


Using Back Button Focus and AI Servo Together

by Hannah Stonehouse Hudson

Using Back Button Focus and AI Servo Together | Life is Short - Find an Adventure - Outdoor Adventures with Hannah Stonehouse Hudson

“If I hold the back button down (while in AI Servo, NOT One Shot – see below), the camera and lens will continually focus on the subject as it moves, so I can stay in one place and capture the action around me.”

“AI Servo (AKA as AF-C on Nikons) is the best auto focus mode for fast moving subjects. AI Servo continues to focus on the subject as long as you hold the back button down. This is perfect for when animals (or humans, or machinery, etc) are moving around you. You can continually frame the shot as you move your camera, holding the back button down, and clicking the shutter when you have an image you like in the frame. This allows you to shoot without burst or sport mode because the camera is focusing on the action as it happens, and you can just click away as the subject goes by without waiting for the camera to re-focus.”

Unfortunately, this does not work in movie mode in my Canon Rebel T6.
Continuous autofocusing is not available in movie mode in that camera model. I will have to record a short movie, stop the recording, recompose my shot and refocus, shoot another short movie, and then string them together later in a film editing computer program.

Thanks for your help.

Steve Thomas

 

[TWX]

Unfortunately, this does not work in movie mode in my Canon Rebel T6.
Continuous autofocusing is not available in movie mode in that camera model. I will have to record a short movie, stop the recording, recompose my shot and refocus, shoot another short movie, and then string them together later in a film editing computer program.

The T6 is a constrast-detect autofocus, right? Since it's in the budget line this unfortunately does not surprise me.

I'd looked into the T6i and T6s, also known as the 750D and 760D, and I ended up with the 77D because the T6s, while being nearly identical to the 77D as the first of the Rebels to have the pro-style top-screen and extra dial around the D-pad on the back, didn't have the latest Dual-Pixel AF sensor. The 77D sits at a weird spot, they named it the 770D for the Chinese market, which pretty clearly establishes its legacy based on the T6s/760D, though amusingly with a model number lower than the T7i/800D that it's a step-up from.

I found a video where someone showed enabling autofocus on the T6, but basically it looks like its AF capabilities are not especially good in live-view or video.



Unfortunately it looks like it autofocuses in video mode about like how my old Rebel XS autofocuses in live-view, which is to say, it really wasn't worthwhile. The XS didn't have video capability at all, live-view was basically only useful for manual focus, and with the low-res screen, it wasn't especially good for that either.

The T6 looks like a nice enough camera for still photography through the viewfinder, basically SLR-style shooting, but doesn't look like it's particularly well suited to live-view stills or video where one wants the camera to automatically handle functions like autofocus.