Hi folks.
I just got a
used Pentax-D Fa* 50mm f/1.4 from KEH for an absolute steal.
However, after using it to shoot a family dinner tonight, I noticed some pretty erratic exposures when reviewing the images on my K-1 (running firmware 2.10, the latest). From one image to the next, the exposure was hopping all over the place. Given that I was shooting in manual mode and in continuous drive mode
(NOT bracketing), this was odd. The exposure ought to have been identical from frame to frame, since the camera's settings and the scene I was shooting weren't changing between shots. One image would be over exposed and the next would be under exposed, and the next after that would be right on the money or, just as likely, two stops too dark.
When I got back home I began running a few tests and
took this video of the issue as it happened.
It looks like the aperture is sticking, but there is not evidence of oil (or anything else) on the blades. The strangest bit of all is that when the aperture gets stuck in the stopped down position, it can be reset by cycling the power switch on the camera body.
This made me start wondering that perhaps this stuck aperture was a firmware issue rather than a sticky blade issue. To test this theory, I repeated my tests on my only other KAF
4 lens, a D-FA 70-210mm; but, the 70-210mm stops down and opens up again just peachy-keen.
If you have had any experience with this, please let me know! I'm thinking that I'll be sending this lens back to KEH for a refund. I would love to keep it if I could get it working properly, it absolutely SLAPS!
Am I missing something obvious, or is this 50mm lens defective?