See soft halo when changing focus on zoom lens

[mlevin77]

I'm using an Alpha 6000 with a Sony E 55-210mm f/4.5-6.3 OSS E-Mount Lens (Silver). I just noticed (when taking pictures of the moonrise, so maybe the weird settings is why I only now saw this) that when I change the focus, there's a very soft (hard to notice, not sharp edges) halo in the image, whose diameter changes as I change the focus back and forth. Any idea what this is likely to be? Normal? Dirt somewhere?