Originally posted by Wormtographer Sorry... the infamous Pentax half dome whitish/yellowish thing has no other function that I know of, other than as an actual landmark, presumably (Asahi Co. presumes) where you are expected to hold the lens--so that you are neither on the focus ring (in this case closer to the front lens element) nor the aperture ring (in this case closer to the camera body).
So the dome just lets you navigate between focus and aperture rings, while giving you a resting ring for your finger.
How cool is that!
Nope.
The dome is an aid to mounting the lens. The dome must match the lens release lever on the body when mounting the lens. Well, that was in the non-autofocus camera days, now the lens release button has moved
It is/was much easier to match the dome (which you can feel with your finger and hence use in the dark) with the release lever than try to find and match the two small red dots
I guess I just revealed my age...