I have an old Pentax 50mm 1:2 lens (from a Pentax Asahi K-1000) and a Vivitar 28mm f2.8 that I am trying to adapt to fit on my Canon Rebel t2i. I purchased two of these adapters but I cannot figure out how to attach them to my lenses. I've watched every video I could find on YouTube, and all of the demos show the adapters simply clicking into place. But when I line up the red dot on the back of the adapter with the red dot on the lens and twist, the adapter gets stuck. See photos for starting and end-stuck positions.
According to the videos I watched, the metal spring should move past the metal ridge until it locks down into place (about 30° I think). I've tried depressing the metal spring and twisting, but that doesn't seem to do anything. I don't have an eyeglasses screwdriver, so I stuck an Xacto knife between the spring and the metal ridge, but the adapter still wouldn't budge.
Both lenses mount on my Pentax K-1000 just fine. What am I doing wrong?