It has a great beam shape in either zoomed or flood positions and I just wanted to further minimize the rings. I thought that they originated from the shiny grease inside the head and removed it but the anodizing is rather reflective by itself, so I actually made it worse.
I think that some members have used kind of a black film, but I can find any reference to a specific kind. Or it could be a matte black grease.
I have a spray tin of heat resisting paint from a car shop, it is fairly matt. It needs heating up for hardening, but if that is not possible: there's no wear inside an aspheric head, it works just as well without hardening.
Actually there might be some wear. If he’s talking about the inside of the bezel, that usually has an o-ring rubbing against it every time the zoom is cycled. Depending on how high quality the light is, the edge of the pill might also scrape slightly against it. Another thing is the inside of the bezel is usually a precision fitted part. If you spray plasti-dip in there, the pill will no longer fit inside.
You can however, paint the inside of the pill and top of the star. That’s a no-wear area.
A couple coats with a “Sharpie” marker will give a near zero-thickness coating with a little anti-wear properties too; good enough to test your ideas without spending much. Not quite a ‘flat’ or ‘matte’ finish but would show if further efforts would be worthwhile. Can be wiped away clean with various paint thinners or alcohol when you want it off.
Thanks guys for your suggestions. Indeed, the reflective tube walls that make some of those rings rub against the inner tube wich holds the pill, so stuff like the liquid rubber would not work there. Actually, I am not sure even the paint would work fine there, so tight is the tolerance there.
But the pill is a definitely shiny area so I will go step by step and paint the pill first using a paint like djozz suggested and see if I can live with the result.