What are the alternatives to the pentax hd d fa 150 450mm f 4 5 5 6 ed dc aw?

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From Pentax HD D FA 150-450mm f/4.5-5.6 ED DC AW: Pentax HD D FA 150-450mm f/4.5-5.6 ED DC AW: A zoom lens by Pentax for Full frame cameras, 150-450mm f/4.5-5.6. Specs - Maker: Pentax - Focal length: 150-450mm (zoom) - Maximum aperture: f/4.5-5.6 (it gets darker as you zoom in) - Made for: Full frame sensors - Mounts: Pentax K - Stabilised: no - Autofocus: yes What it frames like - On full frame (Pentax K): as marked, 150-450mm. - On APS-C (Pentax K): like 225-675mm on full frame; ...

From Wildlife and sport: Reach: Focal length is the first thing to sort out. - Sport from the sideline and larger animals: 70-200mm to 100-400mm on full frame. - Birds: 600mm full-frame equivalent and beyond. Birds are small and far away; a common saying is that you never have enough reach for them. Smaller sensors help here. A 100-400mm lens on APS-C gives the view of about 150-600mm on full frame, and on Micro Four ...

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