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I've owned and played around with the following macro's and macro-zooms on my Pentax K5ii over the last 2.5 years in order from first experienced to last experienced:
Tamron 90mm Macro
Sigma 28-80 Macro
Sigma EX DG 50mm F2.8 Macro
Sigma 18-250mm Macro
Pentax FA 50mm F2.8 Macro
Kiron 105mm F2.4 Macro
Sigma EX DG 70mm F2.8 Macro
Yes I developed an obsession for Macro lenses but I am feeling better now.
For macro and close focus work my favorites were the Pentax FA 50mm the Sigma 70mm and the Kiron 105 F2.4 Macro with honorable mention to the Sigma 18-250 and the Sigma 28-80 Macro.
Here are some examples all hand held:
Kiron 105mm Macro bee on goji berry flower_09-07-2014_190202 Pentax FA 50mm Macro - Really wish Pentax would have made a WR version of this lens. It would make me want to stay with Pentax. It was my favorite Pentax lens period.
mamosa_flower_pentax_50_macro_fa_2013_07_23_184956_IMGP2678 diadophis_punctatus_regalis_oq_2013_08_08_195037_IMGP3461 diadophis_punctatus_regalis_oq_2013_08_08_194307_IMGP3434 Sigma 70mm Macro thamnophis_elegans_vagrans_hybrid_10-22-2014_225854 chickadee_01-09-2015_115916 flowers_10-12-2014_165120
And for those of you who don't like snakes you might not want to see this.
Utah Gartersnake Variety_10-20-2014_174635