I only added my first tamron adaptall lens 2&1/2 years ago & in this order:
Like New 500mm f8 Mirror
Like New 200-500mm f5.6 which came with PK-A adapter ;^)
Carefully used 300mm 2.8
I gotta say Tamron did a heck of a good job on their PK-A adaptall 2 mount. I use the 300mm 2.8 & PK-A with pentax 1.7x manual focus to autofocus assist teleconverter. The 1.7x is an amazing TC, though it is always confused for a true AF teleconverter which it is not.
Tamron did a great job on their old 2003 era discontinued 1.4x AF TC "MC4". Tamron seems to fully understand the workings of the Pentax mounts:
PKA & FA & SDM
As a bonus, if you can locate Pentax Monocular K and use it on 300mm Tamron adaptall 2 if makes a fantastic spotting scope due to the ability to open and close lens aperture. Monocular K is superior to Tamron's own Monocular.
I know all this because I own these items.
So theres nothing stopping you from getting like new used pro caliber Tamron adaptall 2 lenses and PKA adaptall mounts. May take a month or two but they are plentiful enough to find at right price. Out of everything I mentioned The Pentax Monocular K is toughest to locate. But well worth having if you own a 300mm 2.8 Pentax or Tamron. I think its like 31 years old now, from 1978. I found one new in the box a couple years ago.
Originally posted by thibs Agreed. I still think they days of Tamron Adaptall2 lenses was so cool when using multi brand bodies... A shame this isn't possible anymore