Pentax smc da 17 70mm f 4 al if sdm vs pentax 16 85mm f 3 5 5 6?

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From [Pentax smc DA 17-70mm f/4 AL [IF] SDM: Pentax smc DA 17-70mm f/4 AL [IF] SDM](/gear/lenses/pentax-smc-da-17-70mm-f-4-al-if-sdm/): A zoom lens by Pentax for APS-C cameras, 17-70mm f/4. Specs - Maker: Pentax - Focal length: 17-70mm (zoom) - Maximum aperture: f/4 - Made for: APS-C sensors - Mounts: Pentax K - Stabilised: no - Autofocus: yes What it frames like - On APS-C (Pentax K): like 26-105mm on full frame; f/4 gives about the depth of field of f/6 there. - On the larger-sensor bodies of Pentax K: ...

From [Pentax smc DA* 16-50mm f/2.8 ED AL [IF] SDM: Pentax smc DA* 16-50mm f/2.8 ED AL [IF] SDM](/gear/lenses/pentax-smc-da-16-50mm-f-2-8-ed-al-if-sdm/): A zoom lens by Pentax for APS-C cameras, 16-50mm f/2.8. The original DA 16-50, replaced by the PLM version.

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