Richard Bernabe, an internationally renowned landscape, wildlife, and travel photographer, published a review the Canon EF 200-400mm f/4L IS 1.4x lens, a professional “toy” that sells for ridiculous $12,000 (Amazon | Adorama | B&H). He used an EOS 7D and an EOS 5D Mark III for his shootings.

About the auto-focus he writes:

The Canon Camera Museum published the technical report of the EF 200-400mm f/4L IS 1.4x extender lens (Amazon | Adorama | B&H). About the development aims Canon writes:

We revamped four lenses in our EF super-telephoto lens series — the 300mm and 400mm in August 2011 and the 500mm and 600mm in May 2012 — to satisfy professionals and high-end amateurs. This product was developed with the aim of going one step beyond these lenses.

This lens is a super-telephoto lens with a built-in extender that has been newly designed so that one lens can cover a wide variety of shooting conditions and scenes. The extender switch lever lets users quickly switch the focal length range between 200-400mm and 280-560mm in one operation.

The lens carries a combination of fluorite and UD lens elements to deliver the image quality demanded of the super-telephoto lens series while also covering a focal length range of 200mm to 560mm with just one lens.

This high-power zoom lens is further equipped with superb operability alongside image stabilization functionality, reliable water and dust protection, and excellent durability.

The design carries forward the super-telephoto lens series’ design concept and sensibility suitable for a flagship model while aiming for a high-grade feel and presence. The lens silhouette, which tapers from the front toward the mount, expresses the beauty of converging light. Each part has been expressly designed so that photographers can give their full attention to the shot.

You can access the index directly:

Canerastuffreview reviewed the Canon EF 200-400mm f/4L  IS 1.4x lens and once more the outstanding properties of this not so cheap lens are confirmed. They conclude:

The Canon 200-400 mm performed in our test with the highest image quality we have come across for a Canon zoom lens, with and without the 1.4x converter. Flare and ghosts are incredibly well suppressed and in terms of resolution, the camera is likely to be the limiting factor. Professional sports, action, or nature photographers will quickly be convinced of the qualities of the Canon 200-400 mm f/4 with built-in 1.4x converter. Compared to lenses with a fixed focal length, the zoom range of 200 mm to 400 mm zoom delivers an excellent opportunity to frame precisely, while the picture quality remains high.
The sensational built-in converter prevents the laborious procedure of inserting a converter between a camera more than a kilo and a lens of more than 3 kilos. It prevents the frustration of missing just the right shot, because you were inserting a converter between the lens and the camera. The fact that under damp and dusty conditions you need to change the lens as little as possible is also important in order to maintain the highest image quality.

There is much more in the review, as sharpness comparison at different focal lengths, analysis of distortion, vignetting, resolution, center sharpness vs corner sharpness etc.

Lens specs:

• High-Performance Telephoto Zoom Lens
• Canon EF Mount
• Aperture Range f/4-32
• Built-in 1.4x Extender
• Three-Mode Optical Image Stabilization
• Ring USM Autofocus & Internal Focusing System
• Power Focus Mode for Smooth Focus Shift
• One Fluorite and Four UD Lens Elements
• Fluorine Front & Rear Lens Coating
• Highly Resistant to Dust and Water

Canon EF 200-400mm f/4L IS Extender 1.4x
Amazon | Adorama | B&H
rent it at Borrow Lenses

ephotozine posted a set of sample pics shot with the Canon EF 200-400mm f/4L IS 1.4x lens (Amazon | Adorama | B&H) and a Canon EOS-1D X. Regarding the auto-focus they write:

Focus was extremely fast when used in combination with the Canon EOS 1D-X, with AF tracking enabled to keep track of the high speed planes at the airfield.

ephotozine’s post comes with more samples, and a set of pictures of the lens.

Lens specs:

• High-Performance Telephoto Zoom Lens
• Canon EF Mount
• Aperture Range f/4-32
• Built-in 1.4x Extender
• Three-Mode Optical Image Stabilization
• Ring USM Autofocus & Internal Focusing System
• Power Focus Mode for Smooth Focus Shift
• One Fluorite and Four UD Lens Elements
• Fluorine Front & Rear Lens Coating
• Highly Resistant to Dust and Water

Canon EF 200-400mm f/4L IS Extender 1.4x
Amazon | Adorama | B&H
rent it at Borrow Lenses

Lenstip has 36 sample pictures shot with a Canon EF 200-400mm f/4L IS 1.4x (Amazon | Adorama | B&H) lens and a Canon EOS-1D X. Thanks Mark.

As much as this is a highly regarded lens, it is not inexpensive ($11,799).  Hence, someone might be interested to rent the EF 200-400mm f/4L IS 1.4x at Borrow Lenses (click here).

Canon EF 200-400mm f/4L IS Extender 1.4x
Amazon | Adorama | B&H
rent it at Borrow Lenses

• High-Performance Telephoto Zoom Lens
• Canon EF Mount
• Aperture Range f/4-32
• Built-in 1.4x Extender
• Three-Mode Optical Image Stabilization
• Ring USM Autofocus & Internal Focusing System
• Power Focus Mode for Smooth Focus Shift
• One Fluorite and Four UD Lens Elements
• Fluorine Front & Rear Lens Coating
• Highly Resistant to Dust and Water

c|net reviewed the Canon EF 200-400mm f/4L IS with built-in 1.4x extender, a lens that retails for $11,999. They attest a “superb image quality”, and write:

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.

The review has some samples shot with the 200-400mm.