Originally posted by séamuis I just tried four different screw mount lenses on my MX. zeiss planar 50 ZM, auto-takumar 55, super-takumar 55 and SMC Takumar 55. the only one that actually worked was the Zeiss. none of them actually lined up at 12oclock so it would be useless anyway, but the aperture was visible in the window with the zeiss. I believe this is because of the placement of the aperture ring relative to the rear of the lens. the takumar's aperture rings simply aren't far enough forward on the lens to be seen through the window. so aligned or not, I don't think you will be able to utilize the window with takumars.
Thanks séamuis and everyone else who looked into it. I should have said that I knew this was a problem in two dimensions. I did assume that the index mark might not line up at 12:00 on various lenses (some of my Taks do, some don't, on my genuine Pentax adapter when in my ME Super or K20D). What I was more asking, and you just got at, séamuis, was whether the aperture ring was too close to the camera body or too far from it, in some cases, so that the Judas window would miss the entire aperture ring. Sounds like it will be a gamble, varying lens by lens, if I ever get an MX. I love the idea--and the engineering triumph--of a full-info viewfinder accomplished through electromechanical and optical means. (Of course all modern digis have full info, but it's less impressive when accomplished by digital read-outs.) So the MX is on my wish list, or maybe I'll switch it up entirely and get a Minolta SRT-102.
--Dave