Im using a manual pentax 50mm in reverse on extention tubes for on my k50 for macro photographs. I also use a pentax afg-200 flash with diffuser. When i started taking pics with this set up it worked fine but after a while i started seeing a white or over-exposed center of the frame of each shot. This happened to me before with the same set up using my old k-x and then i thought it was not setting up the cam to use old lenses and when i got my k-50 i set it up to use old lenses via the instructions on this site. It works fine with the lenses on not in reverse with no problems. Lenses and mirror are all clean. Anyone els ever have this problem?