Dan, I very often make photos with a black BG obtained in camera in a very simple way: I take a back lit flower against a stark shade that is easy to find with a back light and with a 200mm lens. In this case the BG was the hedge in shade of my garden. Then I expose for the highest tones of light in the subject with the Mode Spot so the BG turns fully under exposure becoming black. If the black is not total I darken it a bit more in PS. In this care there were two small spots left of green that I cloned very easily. In those cases the lens aperture has nothing to do with the BG.
Dan, thanks for your interest in this photo.
Great composition, especially the arrangement of the arcs and in particular the green leaf on the left complementing the pink petal on the right. The silver delineation is the icing on the cake. No nits at all.