Having trouble making a mask without halos

[rbanks88]

I think I must be doing something wrong. Surely Lightroom can make a mask that cleanly darkens an area by -1.00 without creating horrible artifacts.

Here's a detail of the "straight" image:

Here's with the overlay on to show the color range mask. What's causing the white ring?:

Here's what happens when I reduce exposure by 1.00:

Is there a way to avoid the dark and light rings around the area I’m darkening? 

Thanks,
Russell

[Michael J. Hoffman]

It seems to me at first glance, that the image you're editing already has significant artifacts, and by darkening the selected area, you are creating contrast that just amplifies the artifacts in the original image. 

Are the screen shots showing part of the image at 100% zoom (It seems probable). What size is the original image, and what format is the original image? Perhaps it could benefit from some AI sharpening or similar work prior to trying to create a 1-stop adjustment along those edges. 

[rbanks88]

Thanks for the quick response, Michael. 

Those aren't artifacts on the photo—it's a shadow from an outdoor chair, and the sun is passing through a tight plastic mesh as the metal tubes make a dark shadow., creating sort of a moiré effect. But I can see how the software might be confused by it. 

However, I do find, even with clean edges, Lightroom has a tendency to make halos and dark lines (often adjacent to each other) when I make reduce an area's exposure by 1.0 or more. I notice it even more often when I use the HSL luminence slider to darken a specific color. Hence, I’ve started doing that sort of thing with masks, either in Lightroom Photoshop. 

I wonder if having the ability to feather mask edges in Lightroom might help. I find myself sometimes editing the mask Lightroom has made by using the feathered edge of the brush tool. It would be nice just to have feathering slider. Sometimes there's just no alternative to diving in to Photoshop and pushing pixels around!

Thanks for your help,

Russell