Exposure problems with adapted lens

I've attached a couple of my OM lenses and it appears that it is not adjusting the shutter speed correctly. When aperture is wide open it looks fine, but when stopped down to f11 or f16 the image is much darker. It does this in Aperture priority, P or i-auto. I've been through the forum and the settings and can't find anything that might affect this.

Any help would be appreciated.

Edit: I should have added it's an E-P1. The images are underexposed..

 

Underexposed.

 

I played around with it some more today. When using the kit lens I usually have exposure compensation set to -0.3. I changed it to +0.3 and it helps quite a bit. There is still a noticeable difference in the exposure. Not sure if this is normal or not.

I took a set as an example. This is from a Soligor 28mm OM mount that I bought in 1985.

28mm at f4:

Subscribe to see EXIF info for this image (if available)

Same lens at f8:

Subscribe to see EXIF info for this image (if available)

 

Ok, if this is normal that's ok, I can work around it. I thought maybe there was a problem with a setting somewhere. Thanks for the response.

 

I think you are right. I went back and checked EXIF, and they are labeled correctly, based on the shutter speed. These were taken after I changed exposure compensation. I guess it had more of an effect than I thought. These are the only two I took after changing it. So it appears the conclusion is that it's inconsistent, and bracketing is your friend.