I did a quick overview on the lens on Wikipedia. Then I went to B&H to see if it is available and read the reviews. It appears that the Takumar design has been discontinued but they are still available on ebay (and reasonable priced at that) . But I need to read up more on this before I can make any kind of decision. On B&H the few reviews that I read on the Pentax are saying that the 100mm struggles with CA, which was my struggles with this photo. I did find some Groups on Flickr that feature Takumar and will peruse it some later this evening.
Sell me on it. Why Pentax SMC Takumar?