Hello there. I recently got an great kodak aero ektar 7" F2,5. The focusing wide open is a bit hard, but it is logical in that kind of aperture. The problem is that when it is wide open, even focusing in infinity is a little blury, i dont know if this happend in all aero ektars or just in mine. :confused: Then, looking quite hard, i found that te rear element has a diferent serial number to the front element. (I can`t remember right now, but one is EE ans the other EM (1944-1943) So, set the ektar to infinity, and put it wide open, can i find a good sharpen image? Or it is normal that i find a bit blurry image on my ground glass? Regards. And sorry my english.