Originally posted by Marc Sabatella How steady was your tripod? Is it possible the scene changed ever so slightly between shots to cause the meter to read differently? Also, did you try this at a variety of focal lengths? It's possible the lens is telling the camera it's not *quite* f/2.8 at some focal lengths.
Thanks for your reply.
My tripod is not VERY steady but I've done the testing few times and I don't think it's related to the slight movement of the tripod or ball head.
Besides, this issue happens at different focal lengths.
Originally posted by RawheaD Heh, interesting. I'm noticing the same thing :-D
What's funny is that it's also the case even if the shutter speed seems to be correct.
That is, an f2.8 shot @ 1/80s looks brighter (half stop?) than an f4 shot @ 1/40s.
Hmm. Since metering is done wide open, I wonder if the aperture mechanism is closing the blades too far. I.e., the f2.8 shot is the "correct" exposure (since it's shot wide open), but all the other ones are turning out slightly *underexposed*, because the calculated aperture/shutter speed is correct, BUT, the blades are being stopped down about a half stop too far. That's the only mechanism I can think of that'd explain this.
As for Sleepy's example, it's not inconceivable that the calculated shutter speed for f2.8 is 1/60s; it could just be on the border line between 1/60 and 1/80 (I believe there aren't any shutter speeds that would go between those, like 1/70s).
I tried several focal lengths and the problem seems to go away @ 50mm, but any wider... 35mm, 28mm, or 16mm, the same deal.
Very, very interesting.
Thanks for your reply and testing.
I guess there's something wrong with the K-7 since you have the same issue as mine and I don't see this issue on my K10D.
Hopefully Pentax could get the fixed in the next firmware.