7D Mark II - Focus Discussions

This discussion was all in the context of a senior picture shoot. That was clear. What wasn't and still isn't clear is the reason why. He tried several time to explain it to me and said it had something to do with the way continuous drive "overrides" the focus in one shot. Honestly, it doesn't make sense to me either, I'm just sharing what I was told. He was confident in his position and seems to carry some credibility based on his credentials.

On a senior picture shoot hoping with no small movements (lol) I would go with One shot and single drive.

wisv1k wrote in post #17675231
This discussion was all in the context of a senior picture shoot. That was clear. What wasn't and still isn't clear is the reason why. He tried several time to explain it to me and said it had something to do with the way continuous drive "overrides" the focus in one shot. Honestly, it doesn't make sense to me either, I'm just sharing what I was told. He was confident in his position and seems to carry some credibility based on his credentials.

It's easy enough to try it for yourself. Get one-shot AF lock on something, then shoot a burst of shots while aiming your camera all over the place, at different distance subjects. With every Canon camera I've ever owned, I get exactly what I expect: focus distance stays where it got AF lock, no matter where I point the camera while shooting continuous. I count on this to be the case, because I often use one-shot to set focus distance, recompose a bit, and then shoot a burst to ensure I get a keeper (no hand shake, no one blinking or twitching, etc). I'd have noticed if the camera were overriding and refocusing.

Archibald wrote in post #17675222
There are differences...

Check out what Chuck Westfall has to say about it here. (Scroll down a bit.)

That helps clear it up for One Shot vs AI Servo, for me at least. Now the question of Single Shot vs Continuos Drive remains.

mwsilver wrote in post #17675134
... It's unclear why Continuous shooting with One Shot should fail if you are shooting a static object on a tripod unless the issue is the vibration caused by the repeated rapid movement of the mirror.

I agree here, in fact. However, once AF is achieved on your tripod set up, why give the camera reason to adjust? One shot or AI servo, in either case, don't refocus.


IMHO in this example we are just using bad practices to force the camera to find a way to mess up.

Archibald wrote in post #17675140
One Shot allows you to easily recompose without the focus changing on you. ...

How? As soon as you recompose and take another shot, the camera will AF a second time for the re-composed shot.

Unless we are talking about BBF, in which case, both one shot and AI servo will provide the same functionality of NOT refocusing when the shutter is released. In this situation AI servo and One shot will behave the same way.

Archibald wrote in post #17675222
There are differences...
Check out what Chuck Westfall has to say about it here. (Scroll down a bit.)

One really interesting takeaway from Chuck's explanation is that in lower light conditions, One-Shot AF mode is superior to mimicking one-shot by using one of the AI servo modes combined with a quick press and release of the AF-ON button (BBF, long enough to get focus confirmation). He mentions that the One Shot mode actually takes more time to converge on more accurate focus under these conditions. I had always figured these techniques were equivalent in all scenarios, and that BBF users had no reason to ever use One-Shot AF. Now I know better!

IN BBF, One shot, OR AI Servo,

-If you are using BBF, and do not have AF tied to the shutter button,
-If you take your thumb off of the button,

Then the camera IS NOT re-focusing during a burst shot.
Full Stop.

Any missed shot/blur/lack of detail occurring when you are not asking the camera to refocus, when the camera simply CAN NOT refocus, clearly can not be caused by the camera re-focusing.

Find another cause.

- Subject motion,
- Tripod motion, (they are all flexible )
- Mirror slap (rarely the cause, but possible)
- Accidentally touching the manual focus ring,
- Accidentally zooming a non parfocal
- Earthquakes... etc.

If you are shooting in One Shot, with AF tied to the shutter button in burst mode, you are doing it wrong.

My shutter button is meter only. If you are referring to me.

Believe me, I get it. I agree with your assessment 100%. Again, just sharing what I was told.

CyberDyneSystems wrote in post #17675277
IN BBF, One shot, OR AI Servo,
-If you are using BBF, and do not have AF tied to the shutter button,
-If you take your thumb off of the button,
Then the camera IS NOT re-focusing during a burst shot.
Full Stop.

Right. Having an FTM-capable lens, and having FTM available after AF lock (custom function), should be the only way you can re-focus after the lock, during the burst. On some lenses, it is conceivable that this could be done unintentionally due to location and sensitivity of the focus ring, but not super likely.

CyberDyneSystems wrote in post #17675277
If you are shooting in One Shot, with AF tied to the shutter button in burst mode, you are doing it wrong.

I'm doing it wrong then, and getting it to work. I do exactly this, for still subjects, all the time, with and without minor recomposing. Half press to focus, slight (or no) reframing, full press to get a burst. In this context, the point of the burst is either because I'm shooting at the limits of shutter speed I can handhold, or I'm shooting a group of people and I want to be sure I have a shot where no one is blinking, yawning or making a derpy facial expression. Redundancy, basically. I use BBF only for moving subjects, birds and wildlife mostly.

While many shoot static objects using AI servo successfully and I have on occasion use it myself I prefer one shot. I only shoot static in servo when I don't have time to switch.

Ha,...while One shot can and will work with half press most would say your on the wrong side of the tracks. ( just ran outside and pulled the trigger lol ) on this little guy. Yup works.

I do believe that was the first time my camera has been in one shot this year. Took 10 or 12 in just over a second

IMAGE LINK: https://flic.kr/p/xywQ​CX

Jeff nice shot. Were you in One shot mode in continuous or burst mode when you took the picture?

Hey hows your day going Peter ,..that was the entire point to the shot and going out to the garden to do a comparison.

as above in AIservo

IMAGE LINK: https://flic.kr/p/xzaG​mZ