Canon EF 200-400mm f/4L IS USM Extender 1.4x is a top-end telephoto zoom with a built-in switchable teleconverter. c|net has posted a full review of EF 200-400mm f/4L IS with built-in 1.4x extender with some sample images.
An overall conclusion from their review is “superb image quality” for the EF 200-400mm f/4L IS 1.4x lens which is currently priced at $11,999. The super telephoto lens is designed for professional sports and wildlife photographers.
EF 200-400mm f/4L IS 1.4x lens includes an array of top-end features such as Power Focus for movie shooting, and IS “mode 3″ that only applies stabilisation at the point of exposure, aiding panning.
See below for price and availability for this lens.
Canon EF 200-400 f/4L IS USM 1.4x Price and Availability
Canon EF 200-400mm f/4L IS 1.4x Lens Review
From c|net review:
The Canon EF 200-400mm f/4L IS USM Extender 1.4X combines terrific optics, autofocus, and image stabilization with standout flexibility from a built-in telephoto extender.
You get you what you pay for with the Canon EF 200-400mm f/4L IS USM Extender 1.4X: superlative performance and flexibility.