I've found that this depends on the exact mount. I have 2 Tamron Adaptall>P/KA mounts. One allows a maximum aperture of F/4, the other allows up to at least F/2.5 for my 135/2.5. Don't know if one is AD/2 and the other plain Adaptall or just why this is. Haven't taken the time to find out, the 135/2.5 is the only one of 9 Tamron Adaptall lenses that I have that I consider a truly "above average" lens.Don
What are the 8 ones that are average or below? Andre
