Originally posted by MrApollinax And actually this sheds more light on your issue. If I am not mistaken, as I have not shot a fully manual lens on my K100DS for a while, the K100D will take the photo wide open when set to Av. In order for you to stop down the lens and meter correctly using the AE-L button you must be in manual mode.
correct. (I had to dust off a K mount lens to test) when using a manual (pre-A) K mount lens, it will only meter correctly using AV, wide open. when you mount the lens it will stay wide open, no matter what you change the aperture to. so unless you plan on only using the lens at f2, you will have to use M mode and do stop down metering with the AE-L button. with this method, you adjust the aperture to what you would like (you can check DOF by selecting 'optical' in the preview method section in the custom settings menu) then press the AE-L button. this will stop down the lens to the aperture you set (using the aperture ring) meter the light and then set an appropriate shutter speed. then you trip the shutter.
I am going to assume the K100DS' menu is the same as the K110D here.
in the 'custom setting' menu, make sure your settings are like this:
AE-L bttn on M expsr >2
FI with S lens used >2
Using aperture ring >2
Preview method >2
(this one is optional, but needed if you want to check DOF in the viewfinder)