Grossly over exposed images during rapid shooting Canon Mk III

[Bundu]

Recently I had a problem with my new Canon 5D Mk III. My passion is photographing birds in flight and suddenly and ocasionally during rapid shooting the images are grossly over-exposed. I use manual exposure of 7.1 or 8.0, Auto ISO, High-speed continuos shooting, AI Servo AF mode and AF area selection.

The images below illustrate tha issue. All of a sudden the ISO shoots up from 800 in normally exposed images to 12800

in the over-exposed photos?

Has anyone experienced the same problem and if so how was it resolved/

[wq9nsc]

I shoot fast moving sports both indoors and out and when possible I lock shutter speed, F stop, and ISO but if there is tremendous light variance across the field of play then I will set ISO to auto.  I have tried different metering modes and found that evaluative tends to work very well in oddly lit sports venues. I have never run into grossly under or over exposed images in a high speed sequence and I shoot a lot of these sequences with the 1DX 2 set at 14 FPS and the 1DX at 12 FPS.

As I have noted in other threads, I wish Canon manuals had the detail and specificity of the excellent technical writing found in Tektronix test equipment manuals but this metering mode footnote from my 1DX 2 manual may offer a clue as to some of the variation based upon metering mode (paraphrased to avoid having to enter graphic images from camera display screens):

In evaluative metering, the exposure setting will be locked when you press the shutter button halfway and focus is achieved (in one shot AF mode).  In partial, spot, and center weighted, the exposure is set when the shot is taken (Pressing the shutter button halfway does not lock the exposure).

So what happens with exposure lock in servo af mode as to metering in various modes the manual doesn't make clear.  You might try a sequence set to evaluative metering and see if the results are different.  

Rodger

[BurnUnit]

When shooting with Auto ISO, does the camera allow you to set a maximum ISO speed?

[wq9nsc]

At least for the 1DX and 1DX 2 you can restrict the range available to Auto ISO by setting upper and lower limits for auto ISO via the menu and I suspect this is true for the other Canon bodies with auto ISO available.

Depending upon mode and custom settings the camera may override this setting.  It would be nice if these restrictions and exceptions were in easy-to-use table form but with the Canon manuals a lot of the important stuff is in the footnotes. For example if safety shift is enabled, then the actual ISO selected by the camera program can go outside of the restricted range when necessary for to provide for a standard exposure.j

Rodger