Vivitar T01 barrel
The lens barrel with the focus ring on top. This is smooth and resistive. The full throw is about 180 degrees. The front element does not rotate so the use of filters is optimised. The lens also internally focuses so its length does not change. Nice!
This ring also has the distance scale in meters (green) and feet (white).
The second (static) ring marks out the aperture, so this can be read against the distance scale. There is an orange infra-red mark. As is apparent the aperture range is f/2.8 to f/16.
The third ring is the aperture dial itself. This has six rather vague clicks. It is not particularly easy to rotate due to the fourth burled ring, which just sits there but gets in the way of turning the aperture ring.
Something I do not understand: the aperture ring has two sets of markings. One extends from 2.8 (in red) leftwards past 5.6 (in orange) to 16 (marked with a circle). This range is operational. The second set of markings extends to the right with all green numbers. This set is not operational so I don't know why they are here.
Vivitar 28mm 1:2.8 Auto Wide-Angle TX Mount (made by Tokina)