I've recently noticed an oddity with using screwmount lenses in Av on the 
K100D. Underexposure.

I've been testing it today, and I'm seeing 1-2 stops of underexposure, but only 
with screwmount lenses. I get a good exposure with K/M lenses wide open (only 
way they're usable) and good exposure in M mode.

For example, I'm getting 1/160th at f2.8 in manual with the 105/2.8 ST, pointed 
at an evenly lit white sheet of paper in M mode, centre-weighted metering. I'm 
getting 1/400th in Av, all settings being equal (I'm literally twidlling the 
mode dial to compare). The D didn't do this, and I'm getting identical 
exposures with my M 50/2 and Kiron K 28/2, as well as good exposures with the 
DA 16-45 and A 70-210.

This is weird. And sad, I prefer just running in Av mode to pure manual.

-Adam


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