Originally posted by RWJ3399 Might anyone have any suggestions on what I may be doing wrong/if this is a common (and fixable) issue?
Welcome to the Pentax Forums!
As noted above, when using the aperture ring with K-mount lenses on a Pentax dSLR, the lens will remain full open when shooting in any of the automated exposure modes. Likewise, optical DOF preview will also remain wide open. The modes that support aperture ring are M, X, and B.
Since your lens has the "A" position, it is best to leave it there unless it is being used on a bellows or when using extension tubes for close-focus or macro. Doing so will allow support of all automated exposure modes as well as metered manual in M and X modes. P-TTL flash will also work. There is an additional consideration that applies to the Pentax-A 50/1.7, that being that the aperture ring is prone to becoming difficult to move due to breakage of a small plastic part. Prevention is to leave it on the "A" position and not borrow trouble unless it is being used on an older film camera such as an ME Super. If yours does break, there is a fix, but it requires partial disassembly. The aperture ring on my copy of the lens is still good, but it stays on the "A" position.
Steve