Is the pentax smc d fa macro 50mm f 2 8 worth buying used?

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From Pentax smc D FA Macro 50mm f/2.8: Pentax smc D FA Macro 50mm f/2.8: A macro lens by Pentax for Full frame cameras, 50mm f/2.8. Specs - Maker: Pentax - Focal length: 50mm (macro) - Maximum aperture: f/2.8 - Made for: Full frame sensors - Mounts: Pentax K - Stabilised: no - Autofocus: yes What it frames like - On full frame (Pentax K): as marked, 50mm. - On APS-C (Pentax K): like 75mm on full frame; f/2.8 gives about the depth of field ...

From Pentax smc D FA Macro 100mm f/2.8 WR: Pentax smc D FA Macro 100mm f/2.8 WR: A macro lens by Pentax for Full frame cameras, 100mm f/2.8. The earlier weather-sealed 100mm macro, with a different optical design from the HD D FA ED AW version.

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