1DX bracketing & focussing

Just a quick query as I never had this problem before.

When you set your 1dx to auto bracketing my understanding is the auto focus will focus the camera at the outset and will then take all 7 bracketed shots without refocusing.
I have done thousands of bracketed shots over a number of years and never had an issue before but tonight I was doing a low light shot at Manchester airport in auto focus on my 70-200 f2.8 mk2. Tripod mounted with IS turned off and the 2 second shutter release used to eliminate vibration etc. The first and last shots were spot on but the shots in between are out of focus.

To avoid this occuing further I reverted to manual focus for the rest of the shoot.

10 weeks ago Canon replaced the shutter assembly to try and fix the muck on sensor issue but I am now thinking that this may be causing a focus issue.

Hoping someone might be able to give me some thoughts as I am probably going to have to send it back yet again !!!

Might be a stupid suggestion but you weren't in Servo mode by any chance?

I have not encountered this problem with my 1DX, perhaps because I us Back Button focus so my AF is off when I take my thumb off the AF on button. Might work for you, I find it much better than using the shutter release button for AF but it can take some getting used to.

Thanks
I will check the servo mode setting and see what that setting was on but it has never affected the shots previously. When I do these they are shutter remote shutter release or timer release so the camera is never touched while the bracketed shots are happening to avoid any shake or movement. With the 2 sec timer release the camera will take all 7 shots automatically one after the other so the shutter button is never touched.

But the main issue is I don't believe that the camera should change focus during the bracketing series. The first bracketed image is sharp and several in the series are out of focus slightly. I have never encountered this in tens of thousand bracketed photos but last night in auto focus that is all it would give me.

If you have focus on the shutter button, and are in AI Servo mode then the AF will be constantly on while you hold the shutter button. It won't matter if you are using the buttons on the camera, or the one on the release. AI Servo assumes that you want to track the subject no matter what else the camera is doing. If you are tracking a moving subject, you still might want to bracket the exposure, especially if it is a difficult situation. It would not be good of the AF system was stopped during that process. If you want the AF to be locked, use the camera in One Shot AF mode which stays fixed once the camera has locked focus, or use MF.

Alan

I understand the fact that if you are continiously pressing the shutter release for each of the bracketed shots then it will keep tracking a moving subject and refocus but when you shoot bracketed and use the 2 second delay timer shutter it will take all 7 shots one after the next automatically without you having to touch the camera so why would the focus change?
I have shot like this for years and never noticed a problem until last night and it is the first time since the shutter assembly was replaced.

It doesn't help the Op with the problem here, but it's interesting to see how differently we use our cameras. I've had Canon cameras with bracketing capability since 1991, but I've used it ten times, I think. Eight of these to test how it worked.