Random EXIF data with same camera settings

Question

I have a few problems with exposition with my Canon 70D: with same camera settings I get random EXIF data for focal lenght and aperture.

This is the setup

Table with white paper as white background.
Two strobe flash lights with umbrellas at the each side about 45° angle (triggered by hot shoe trigger on camera) manually set power, no TTL.
Canon 70D camera on tripod.
Camera settings in "M": ISO 100, 1/160, f9.0, Metering Mode: Evaluative metering.
I use a 18% grey card to get proper white balance, set the WB to "custom" and get the WB data from the picture of the grey card.
I also use an exposimeter to check that I have the best metering and it is all fine.
Subjects are bags or similar leather products.

After I take pictures, that should all be the same exposition, I notice that there are a few difference between the photos. In fact I took two consecutive photos, not touching the camera or anything, of the same subject on the table, and one looks darker than the other (actually I can't show the products because they are trademarks).

Surprisingly, when I went to check the EXIF data, I found that they are quite different than the camera setup, and that seems explaining why some photos are darker/brighter than others.

Why that happens? Is my camera malfunctioning?

Please check the two screenshots (sorry the software is not in english but you can guess...=.

Mario · Accepted Answer

I could finally verify that the problem was 100% caused by the lens. It was internally unstable and in certain position the internal connections were not communicating the right values to the camera body (or they were completely isolated).
This problem seems at first random happening, then after more shootings it got worse and in the end the lens got stuck and would not zoom anymore. If you shake the lens, you can hear some little thing (maybe a little screw) going around.

Michael C · Answer

It looks like you've probably got 'Safety Shift' enabled and set to option 1: 'Shutter speed/Aperture' in your 70D's menu. It's found under the "Custom Functions" menu at 'Menu → Custom Functions (Orange Tab) → C.Fn I: Exposure → C.Fn I -6 Safety Shift'.

It also looks like you're using a manual flash triggering method that the camera does not detect.

Thus your camera is not taking into account any of the light from the flashes and is assuming only the ambient light is there to illuminate your subjects.

It's all covered on page 367 of the EOS 70D Instruction Manual

Random EXIF data with same camera settings

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