Sigma 400mm f/5.6 APO (manual focus) + 2x TC: my review.: Pentax SLR Talk Forum: Digital Photography Review
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Sigma / Carl Zeiss Jena (AF and MF) IF MC multic 400mm F5.6 Lens Reviews - Sigma Lenses - Pentax Lens Review Database
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Re: Anyone tried Sigma 400mm f/5.6 Tele-macro on K-1 yet?: Pentax SLR Talk Forum: Digital Photography Review
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