| That looks like a really really good eyecup. I have not seen it on any Pentax Camera until now. The big hard rubber thingie of the 645 is not the greatest, especially if you were eyeglasses.
I had a more flexible screw on eyecup that was lying around and it roughly fits the thread on the 645 eyepiece. The fit was not perfect and I use two drops of red locktite to secure it. |