Hi Littledrawe,
Nice to see your post
I actually have exactly the same extension tubes, found second hands for few bucks recently, and also had trouble in making a proper macro picture.
I used a manual facus pentax 50mm /1.7 A lens for that, and I noticed that I can not set the aperture (manually on the lens or via the camera in Av mode) as required.
When mounting the tube on the lens, everything looks ok. Moving manually the small metallic "finger" (what's the name in english?) would trigger the diaphragm properly.
But when I mount the lens+ tube on the K5, while turning to fix it, I can see the diaphrag opening as wide as possible (so it sticks f1.7) and nothing can be done to close it.
I guess that what you have too, overexposure because your lens is actually opened at its maximum and not at the f16 value you set.
If somebody knows how to fix that