Shutter speed changed itself?
 

4 shots taken within 10 seconds; no light change. All @ AV and f/7.1; Spot Metering and ISO 400
1. 1/4000
2. 1/1600
3. 1/1000
4. 1/4000

Why did shutter speeds change and how do I get Mk II to optimize the scene, (by choosing #2 or #3 automatically like my 40D does in AV)?

Did you press the AE-lock button? That normally eliminates such changes.

In any case, on Tuesday or so we should have new firmware available that will give us manual control. No one outside of Canon and their partners knows exactly what to expect, but you should be able to avoid the changes that you recently experienced.

Thank you very much Jon. No, silly me, I did not even think of pressing AE-lock button and I shall test that today. It appears that AV Mode on Mk II is not as intuitive as it is on 40D?

Right now, everything is automatic in video mode. There is no M, Av or Ap for 5D Video. However, the new firmware should give us "M" mode. Hopefully, we'll get Av and Ap as well. We will see!

Are we talking still photos or video here? I think that Brendan is talking about stills as video never has a shutter speed of 1/4000. John certainly is talking about video. The Exposure Lock button does function for stills but you wouldn't normally use it for repeated shots of the same subject without changing light conditions.

I am not sure why the exposure should vary like that shot from shot. I do find that in automatic mode when fixing the aperture that the shutter isn't always correct & after reviewing the photo I sometimes need to switch to manual to get the correct exposure.

Thank you, for hitting the nail on the head, Nigel. The images above are stills.

In Live View Function settings I selected Stills & Movie. It may be that Jon is implying that if I had selected "Stills only" (and AE Lock?) I would have had the intuitive response I get from 40D, [that is, in AV Mode I select the f/stop, ISO, metering, WB and let the camera find the fastest shutter speed in the prevailing conditions of light and camera shake].

But now you have defined the problem well and I look forward to more answers.

If you used spot metering, then it isn't surprising that the exposure changed a bit between shots in a scene that contains a lot of contrast. In spot metering, just the small circle in the center of the viewfinder is used for metering.

Amn't I glad I asked the question and I thank you all for developing the question so that Pete could answer it. All my centre-focus-points were off the birds ... so that's when to think twice or more before spot-metering. Thank you very much, Pete. I wish I could have found that out for myself but, hopefully I'll know the next time.