I recently got a SEL50F18 OSS APS-C Lens for my Sony a6000. As it is my highest aperture lens (f/1.8), I did some experimentation with raw files and tried to push the limits in Lightroom with highlights and shadows. I do know that my Sony a6000 hasn't the biggest sensor, but it's currently my highest dynamic range camera (vs. Nikon D5000). The problem also only occurs with this lens.
I chose this picture, taken with full aperture, as it has the most problem with increasing the shadows. Depending on the dynamic range of the image, the problem isn't as visible.
While I can without problems lower the highlights to -100 in Lightroom to recover awesome details, I can't increase shadows over +10 without revealing this polygonal artifact.
raw unedited exported to jpeg:
raw highlights -100; shadows +100: exported to jpeg
Here is a version with heavily increased brightness to expose more of the shape:
I don't understand this behavior at all. I'd be very happy if someone could explain why this happens when boosting the shadows and how I can prevent it and still have the ability to recover depth data.
Note that this does not occur when focus point is on a near object with indirect lighting.