There are 2 versions of this lens. They look exactly the same. To tell the difference, look below the switch on the lens. If it ends with '1' its a version one lens. If it ends with '2' its a version two lens. The SMC 'K' version that Thoth has is the same as the version 2 lens. (ie. the K mount version of it) I have all 3, and personally, I find that the version 1 has a more gentle rendering, a bit less warm in color and little less contrast. However, I do find it to be a very nice lens and often prefer this style over the punchier ver 2 (bolder drawing style; more contrast). Ver1
http://www.flickr.com/photos/29329237@N07/8701181479/ 20130501-IMG_0119Canon EOS 5D by , on Flickr At about $180, I suspect its ver 1, but even that is a good price. Edit : There is a 135mm named as "K mount Takumar 135 f2.5" and you need to be a bit wary of this one. (ie. its not the SMC K135/2.5) This was a low end lens that was made in later years using the Takumar name and is often considered the worst of the Pentax 135mm Not that its totally bad, but the rest are considered better.