Ah, good for you to notice. That was 1000mm f/11 Nikkor Reflex cata-dioptric lens. Invented by the Russian genius lens designer Maksutov in th 1800's, the light going through this lens is reflected by a parabolic mirror into a small mirror in the center of the lens and back to the sensor, this lens was a prototype of the first telescope. Its donut-like bokeh is a signature of all mirror lenses known as "poor-man's long lens".
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