My opinion is there is a non compatibility between some lenses and camera electronic. Mirror flops happens to my K-r on these casses:
Pentax 50mm f1.4: never
Pentax 18-55mm kit lens: never
Pentax 35mm f2.4: never
Pentax 135mm f2.5: never
Sigma 18-200mm f3.5-6.3: never
Vivitar 70-210mm f2.8-4.0: usually
Samyang 18-28mm f4-4.5: sometimes
Carl Zeiss 50mm f1.7 contax mount converted to PK: allways
Rikenon Ricoh XR 28mm f2.8: never
So, on my experience using different kind of lenses, mount material, wrong pin connections, or metering reading, donīt really knows for sure, produce the effect of erratic mirror flops.
Last edited by wax; 09-16-2011 at 03:24 PM.
Reason: actualization 16709/2011