Haloing in focus stacks often happens when each source frame has very shallow depth of field, so edge transitions don’t overlap cleanly. Based on the result reported here, stopping down from about f/3.2 to f/8 solved the problem because each frame contained more in-focus detail and smoother overlap between slices.

So the main fix is to capture the stack with greater depth of field per shot:

• use a smaller aperture, such as f/8
• keep enough overlap between focus steps
• avoid changing composition between frames

If Helicon Focus radius changes don’t help, the issue is likely in the capture rather than the render settings. In macro work, a slightly narrower aperture usually reduces stacking artifacts much more effectively than trying to correct halos afterward in software.

In short: to avoid halos, increase depth of field in the source images and ensure the stack has adequate overlap.