To be frank, I discovered the above (effect of LED centering ring) accidentally.
I had my original Astrolux S2, showed it to an acquaintance who also wanted one and I ordered for him. When I tested the new Astrolux S2 and my older Astrolux S2, I noticed that my Astrolux S2 didn’t have a donut hole, whereas the new Astrolux S2 has a donut hole (at short distances).
I was wondering what’s the difference between the old and the new Astrolux S2 — and on closer inspection, that’s when I noticed that my original S2 does NOT have a centering ring on it, whereas the new one has the centering ring (causing the donut hole).
If I had known my original S2 was missing a LED centering ring I would have complained to Banggood about the missing part, but that’s already been several months ago). Anyway, I have been using my Astrolux S2 (with the missing centering ring) for some time now, and have not experienced anything out of the ordinary — hoping there wouldn’t be a risk for it to get a short?