I went to Bojidar's fantastic pentax site site and found this camera you mentioned from 1981.
http://kmp.bdimitrov.de/bodies/photos/ME_F_AF35-70f2.8.jpg
So its been just 28 years since pentax had autofocus, I wonder when they'll make a fully fuctional 1.4x autofocus teleconverter? You know, for sale not simply roadmapped. I always thought it had only been 22 years since they had AF with a 1987 issue date. But with an extra 6 years, one might assume an AF 1.4x TC may have gotten made two decades ago? I wonder what the engineering problems are to have taken this long?
I own a Tamron 1.4x MC4 and it auto focuses my slow aperture FA 80-320mm f5.6. So I do know its possible and this Tamron AF TC was discontinued like 5 years ago. I'm told that it offers full compatibility with SDM glass but I own no SDM glass.
Originally posted by Pål Jensen It is written by engineers with diagrams and illustration.
You are confusing AF point with sensors. Each AF point have two sensors; that is what the beam splitter is used for; splitting the beam to each sensor.
It is not correct that AF do not work at aperture slower than F:5.6. It has nothing to with blacking out as stated earlier. It works, but that depends on brightmess and contrast of the subject. It is just that it doens't work consistently enough. This according to Pentax technical paper. It has also been collaborated by user who has managed to get F:8 lenses to AF.
To me Canon F:2.8 AF looks like marketing speak as Pentax had this feature in the first AF SLR, the Pentax ME-F of 1981. It was manually engaged via a switch on the top of the camera body. Canon seem to do this automatically, I wont be surprised if Pentax does that to now that all lens info is transmitted to the camera....