Is the canon ef 200 400mm f 4l is usm extender 1 4x good on aps c?

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From Canon EF 200-400mm f/4L IS USM Extender 1.4x: Canon EF 200-400mm f/4L IS USM Extender 1.4x: A zoom lens by Canon for Full frame cameras, 200-400mm f/4. A professional wildlife zoom with a built-in 1.4x teleconverter. Specs - Maker: Canon - Focal length: 200-400mm (zoom) - Maximum aperture: f/4 - Made for: Full frame sensors - Mounts: Canon EF - Stabilised: yes - Autofocus: yes What it frames like - On full frame (Canon EF): as marked, 200-400mm. - On APS-C (Canon) (Canon EF): like 320-640mm ...

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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