5d mk3 Ai servo and recompose at half pressed button

I noticed that on AI servo and having the focus point central that once I recomposed (button still half pressed) it tried to re- focus on the centre point again..
Am I doing something wrong (settings)?

AI Servo is for things in motion. If you're shooting still subjects, use oneshot. AI Servo will follow the established focus point if you move the camera.

You should be using the back button focus function.

Wallace River wrote in post #16514378
AI Servo is for things in motion. If you're shooting still subjects, use oneshot. AI Servo will follow the established focus point if you move the camera.

Yes but many on this forum believe that AI servo is the best setting even with portraits as the subjects can move a lot..

Nick_Reading.UK wrote in post #16514396
Yes but many on this forum believe that AI servo is the best setting even with portraits as the subjects can move a lot..

In this case you select the proper Af point.

For recompose you can either use BBF with AF removed from shutter(lift thump off back button when recomposing) or you could also set back button to AF stop which will stop the shutter from focusing.

Wallace River wrote in post #16514378
AI Servo is for things in motion. If you're shooting still subjects, use oneshot. AI Servo will follow the established focus point if you move the camera.

This..

Nick_Reading.UK wrote in post #16514396
Yes but many on this forum believe that AI servo is the best setting even with portraits as the subjects can move a lot..

I read this forum a lot and I don't remember seeing this.

saea501 wrote in post #16514420
I read this forum a lot and I don't remember seeing this.

https://photography-on-the.net …/showthread.php​?t=1344042

Al servo on 5D3 is *almost* as accurate as one shot even for still subject. Thus mine is on al servo 100% of the time.

To answer OP's question, of course the camera will try to refocus! That's the whole point of al servo!

People use 5D3 mainly to move away from focus recompose as it has so many available points for you to choose from.....using center point then recompose isn't how 5D3 is meant to be used....you have 6D for that

If you insist, either use bbf, assign a button to stop AF, or switch to one-shot mode.

kin2son wrote in post #16514481
Al servo on 5D3 is *almost* as accurate as one shot even for still subject. Thus mine is on al servo 100% of the time.

To answer OP's question, of course the camera will try to refocus! That's the whole point of al servo!

People use 5D3 mainly to move away from focus recompose as it has so many available points for you to choose from.....using center point then recompose isn't how 5D3 is meant to be used....you have 6D for that

If you insist, either use bbf, assign a button to stop AF, or switch to one-shot mode.

True, I need to get quicker at moving my focal points...

Nick_Reading.UK wrote in post #16514367
I noticed that on AI servo and having the focus point central that once I recomposed (button still half pressed) it tried to re- focus on the centre point again..
Am I doing something wrong (settings)?

Yes, you are doing something wrong, you cannot focus recompose with AI servo active. To be able to recompose the picture you need to lock focus before you move the AF point, in one shot focus the camera locks the focus when you half press the shutter, so you can move the camera around and focus doesn't change. The whole point of AI servo is that it never locks focus, so long as your finger is pressing the button it will continuously be refocusing on whatever is under the AF point.

Therefore if you focus on your subject and recompose so the AF point is over something else, it will focus on that instead (as you are seeing). You can use back button focusing to select focus on your subject, then release the back button to lock focus and allow you to recompose, but then you are effectively using one shot and not AI servo.

If you want to use AI servo, then you need to select a suitable AF point and keep that where you want to focus (on the nearest eye in the case of a portrait).

AI servo can be better for portraits when either you or the subject are moving, particularly when shooting wide apertures for shallow DOF. If you are using smaller apertures and neither of you is moving around much, then one shot and focus recompose will be OK.

Nick_Reading.UK wrote in post #16514367
I noticed that on AI servo and having the focus point central that once I recomposed (button still half pressed) it tried to re- focus on the centre point again..
Am I doing something wrong (settings)?

Just confirming what was said above, you are using the wrong AF mode. AI servo is designed to track moving subjects. It does this by constantly refocusing (never locks focus in the way One Shot does). So, when you move the AF point off your subject to recompose the camera refocuses on whatever is now under the selected FP.

Two solutions.
1. Change to one shot mode.
2. Set up the camera for Back Button Focus - This takes focusing off the shutter button onto a separate button. You can then press the back button to fucus, release it to "lock" focus, recompose and then press the shutter button to take the image without the camera refocusing.

I use option 2 as my camera is almost always in AI Servo mode.

Nick_Reading.UK wrote in post #16514490
True, I need to get quicker at moving my focal points...

Setup separate points for horizontal and vertical shooting positions. In addition program AF-ON button to use center AF point.

On 5dmk3 I don't mind using AI servo even for still targets. Just need to make sure 1) Keep AF point on target all the time, or 2) Release back button focus and make sure shutter is not setup to AF. In my older camera moving AF from shutter button to back button would remove AF from the shutter. On 5dmk3, you can have AF both on the shutter and back buttons (* and AF-ON) at same time, so 3 separate buttons doing AF in AI servo mode.

You should be using the back button focus function.

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Even with BBF if OP re-composes, he is messed up, isn't it?