---------- Post added 11-26-19 at 07:27 PM ----------
The aperture ring is mounted near the front of the lens. I found it very easy to grasp with the grooved or serrated surface and due to its positioning, no hunting. ........There are six settings/positions: 16.. 11.. 8.. 5.6.. 4.. 2.8. No button(s) on this 24mm and I can't comment further, as I am very unfamiliar.
The green marking of " 24mm" (without quotes) is next to the 2.8 setting. The wider focus ring, located closer to the mount, works nicely.
Give me a shout if you have a comment or question and I'll try...........
Regards
jake
---------- Post added 11-27-19 at 10:49 AM ----------
You are right, there is no button for preview. The lens is stopped down using the aperture ring with the 6 positions illustrated in the photo. Through the viewfinder on my K5IIs the changes can be seen when rotating the aperture ring.
Last edited by jakester11; 11-26-2019 at 07:28 PM.