The Canon mount is bigger than the Pentax K mount, so I don't think you can adapt it easily, unless you use something like bellows, but this affects the focus range and increases magnification. That Canon lens is a really niche lens, Pentax has no native enlarger lenses right now.
I recently read the Tokina 100mm is the same optical design as the Pentax DFA 100mm (and previous Pentax 100mm like the non-WR DFA, FA, F). The Tokina has advantage that it has aperture ring and focus limiter. Pentax DFA 100mm WR has aluminium body, SMC coatings, WR and QS, and its smaller. So no, I don't think the Tokina will come out in Pentax K. Its one of the collaborations between Pentax and Tokina.
You can buy the older DFA version (has focus clamp and aperture ring, no limiter, no WR, and its bigger) or FA and F version (I think one of these has a focus limiter as well) for a good price. But honestly, I think the DFA 100mm WR is still priced very fairly. Its a great lens. More info about the Pentax 100mm lenses here:
https://www.pentaxforums.com/lensreviews/showcat.php?mcats=all&what=titledesc...=0&firstpost=1
Just keep in mind that the ones older than F series have slower aperture and might only have 1:2 magnification.
If you want to go beyond 1x magnification, you can try bellows and extension tubes, but for those you need a lens with aperture ring (so don't get the DFA 100mm WR). You can also look at the
Venus macro lenses that have recently been announced, they seem interesting. Fully manual, but you don't really need AF in the macro range.
Btw, there are a couple threads like "
macro by any means necessary", with great tips on how to use affordable lenses, reversing them, using tubes and bellows, to get really really good magnification.
Originally posted by naldopr 
Post #3 by stevebrot
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