The infamous "mirror flop" problems reported by users of various Pentax DSLR cameras may be caused by a malfunctioning aperture control mechanism. In this video, I simulate an aperture mechanism fault by holding down the aperture lever on a Pentax K-r and attempting to operate the camera with the lever held down. The camera, which otherwise functions normally, starts mirror flopping once I power cycle it, yet the camera returns to normal as soon as I let go of the aperture lever.
This explanation for the mirror flop problem applies primarily to less advanced Pentax camera models which have a linked aperture and mirror mechanism, including the K-r, K-30, and K-50. I'm not sure whether this holds for the Pentax K-7, K-5, or K-3, which do have independent motors for the mirror, shutter, and aperture lever, but it's entirely possible for this to be the cause of the mirror flop issues in these cameras. I've written about this before at http://www.pentaxforums.com/forums/6-pentax-dslr-discussion/189224-mirror-flop-problem-revisited.html.
While I've done this before without damaging the camera, please note that I am not responsible for any damage to your camera resulting from the procedure demonstrated here. This video was shot with a Pentax K-5 and D FA 50mm Macro lens.
