Is the pentax hd da 15mm f 4 ed al limited worth buying used?

Here is what the site says about that.

From Pentax HD DA 15mm f/4 ED AL Limited: Pentax HD DA 15mm f/4 ED AL Limited: A prime lens by Pentax for APS-C cameras, 15mm f/4. Specs - Maker: Pentax - Focal length: 15mm (prime) - 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 22mm 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 HD DA 21mm f/3.2 AL Limited: Pentax HD DA 21mm f/3.2 AL Limited: A prime lens by Pentax for APS-C cameras, 21mm f/3.2.

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