Pentax's premium DX telephoto prime — the DA 300mm f/4 with SDM motor and weather sealing.
The Pentax SMC DA 300mm f/4 ED IF SDM is a super-telephoto prime from Pentax for their K-mount APS-C DSLR cameras, providing a 450mm full-frame equivalent field of view. ED glass controls chromatic aberration at this focal length, IF maintains constant barrel length, and SDM provides fast and quiet autofocus.
The lens delivers 300mm (450mm equivalent on APS-C) at f/4, with ED glass, internal focusing (IF), SDM autofocus motor, and an APS-C DA image circle. Weather-resistant construction is included.
At 450mm equivalent on APS-C, the DA 300mm f/4 provides strong wildlife and sports reach with the fast SDM autofocus needed for tracking moving subjects. The DA-only designation means it is optimised for APS-C sensors. Pentax in-body SR stabilisation applies.
Test SDM autofocus tracking speed at 300mm. Verify ED glass condition. Check IF mechanism (barrel should not extend during focus). Inspect weather seals. Test focus accuracy at distance for sports/wildlife use.