That’s not a deliberate effect. This is just how the Reflex Nikkor 500/8 renders bokeh. The mirror inside the lens is essentially doughnut shaped and reflects the image back into itself. So technically speaking, there is a massive gaping hole in the middle of the lens. This is why you see the ring effect in the out-of-focus blur.
What is the effect toward the bottom that looks like a line of circles?
That’s not a deliberate effect. This is just how the Reflex Nikkor 500/8 renders bokeh. The mirror inside the lens is essentially doughnut shaped and reflects the image back into itself. So technically speaking, there is a massive gaping hole in the middle of the lens. This is why you see the ring effect in the out-of-focus blur.
Edit: Corrected a Typo.