Originally posted by crossover37 So I took two test shots with my camera and I shot the first one at F1.4, ISO 1600, 1/125...the second shot is F2.8, ISO 6400, 1/125. Both of the shots should have the same amount of light but why is the one shot at F2.8 ISO 6400 brighter? The depth of field is shallower though. I bought this lens used and was testing it out.
F1.4, ISO 1600, 1/125
IMGP8942 | Flickr - Photo Sharing!
F2.8, ISO 6400, 1/125
IMGP8943 | Flickr - Photo Sharing! If your lens is missing an A position on the aperture ring, or if you turned the aperture ring off the A position, the lens will only stop down in M mode. In Av mode (the only other mode the camera will use with a lens without the A position) the lens does not stop down, but rather shoots always wide open. This would account for the brighter image at 6400 - two stops more light than at 1600.
There are well documented metering errors with anything from the K10d (which I own) and later camera bodies when the lens is not set to an automatic aperture. The lens will expose in M mode correctly at only one aperture, and will overexpose in one direction and underexpose in the other.
The problem is specifically with the focusing screen which is designed, in the later cameras, to give a brighter image. Replacing the focusing screen with the L series screen (I personally have the LL-60 with grid lines) results in accurate metering. I was worried that it would cause erroneous exposure with the DA lenses, but they expose the same. I use five lenses routinely, my three DA series and my two M series lenses. Replacing the focusing screen with the LL-60 gave me correct metering with all five lenses - and anything else I put on the front from time to time.