I'm using the EF 100mm f/2.0 USM lens on an EOS 5D Mark IV body. There seems to be a specific focusing distance (about 1.5 m) below which all photos come out at least one stop underexposed when relying on the camera's metering system.
The following two photos were both taken through the viewfinder in aperture priority mode using evaluative metering. The subject distance is about 1.5 m.
As you can see, the camera's metering system chose a much darker exposure for the first photo, with the only difference being that the camera was slightly further away from the target in the second photo.
This happens in both AF and MF and seems to depend solely on the focusing distance, rather than the actual subject distance. When changing focus in MF mode, I can easily see the jump the metering system does when crossing the focusing distance at which the effect starts. I can provide more examples if needed.
This does not happen in live view. It seems to be specific to mounting the EF 100mm f/2.0 USM lens on the EOS 5D Mark IV body, as it does not happen with any of my other lenses on the EOS 5D Mark IV body and it also does not happen with the 100mm f/2.0 USM lens on my EOS 750D body. Both bodies and the lens in question run the most recent firmware at the time of writing this.
What is causing this effect? I will probably return the lens since this makes shooting with it very difficult and I didn't like it that much overall anyways, but it would be nice to know what is wrong so I can avoid this problem in the future.
I do not think that my question is a duplicate of this question. The jump in exposure is very sharp and happens at a specific focusing distance, rather than continuously changing with focusing distance as I would expect with light loss at high magnification factors. Furthermore, the magnification is not particularly high as the subject distance is about 1.5 m. I am fairly certain that the issue is with the metering. Indeed, when using manual mode to circumvent all metering or live view shooting to use a different metering system, everything works as expected.