Aperture ring on a lens/zoom evolves over the years, from a ring with aperture values, auto-gear/lock ring to no ring on a current digital lens. However, this Vivitar lens has a unique ring, which can be turned to both sides for auto or manual aperture sizes. The 'auto' here means that the aperture keeps open at 2.8 until the shutter button is pressed and the aperture reduces the size you set during the exposing.
The lens front piece turns during focusing. The lens length extends a little bit when focused to the shortest distance
There are five aperture blades, which do not form a regular-shape hole at the smallest aperture setting.
Interesting. I've never seen one like this before.
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