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So many options ...
Sigma 105 ....
I own a few lenses , and if you can find one , try the Pentax A 100mm F4 Macro ( 1:2 ) , + a Pentax No1 close focus filter ..
If you want Auto focus , and $$ is not the issue , Sigma 105
Pentax lenses have a good rep overall .. + Plenty of used ones on Ebay
Tamron 90mm is certainly good enough , if the price is right .
I wish I owned them all ,
But my sharpest results have come from 50mm lenses combined with Tele macro converters ...
And soon ( come summer ) I will run all my lenses through a K20D to see whats what ... And after that , ill be selling stuff on Ebay ...