Lens focuses very fast and accurate, great for birds in flight and other wildlife, light enough to carry all day and use hand held. However this lens is slow so it needs a lot of light. Wish canon would make the same lens with IS at a price mortals can afford.

extremely fast focus and light weight

needs lots of light to perform well

I bought this to replace another lens that failed several years ago, so I have had plenty of experience with it shooting various wildlife, primarily birds for large prints, typically up to 36 inches on a side, using a Canon 40D, then a 60D.This lens is capable of extremely high IQ images.

Consistent Output; Durable; Easily Interchangeable; Fast / accurate auto-focus; Lightweight

Maybe Soft Wfilters; Maybe Soft W Filters

A good entry level bird/wildlife lens. Takes a bit of practice to get sharp shots handheld.

Well made; Sharp; Not too heavy for a 400, but not exactly light either; Good value; Works pretty well with the 1.4x extender; Fast autofocus

It could really use IS

I purchased this lens for bird photography and am very happy with it so far. It is lighter than the 100-400mm Canon and have found that all my pictures are at 400mm anyhow. The lack of IS might be a problem for some especially in dusk/dawn situations when you need to slow the shutter down.

Durable; Fast / accurate auto-focus; Lightweight; Rugged; Strong Construction

Poor in Low Light

Brilliant optics, tack sharp wide open with aps-c , razor sharp on FF !! Wish canon had added IS to it to compensate for the slow aperture.

A very fast focusing lens on canon. MTF chart of the lens says all about the picture quality

I bought this for a trip to BC/Alaska, and it's my first Canon L lens. It may have cost me an arm and a leg, but it is solidly built and focuses very fast. I bought a monopod at the same time but it could really do with a pistol grip screwed into the lens's tripod bush when you're shooting hand-held...

I'm using this lens and an EOS 700D on an internet controlled astrograph. The build and the image quality over the entire field are both absolutely superb. Ultimate picture quality appears to be limited by the camera sensor, rather than the lens. Just amazing. Next, a x2 extender.

Canon classifies the Canon EF 400mm f/5.6L USM Lens as a "Super Telephoto" lens. It is super in image and build quality , but is not super in size . The 400 f/5.6 is relatively light in weight but very solidly built . It feels long and narrow in your hand - and feels even lighter than it is.

Never liked the EF 300 MM F4.0, the EF 100-400 mm was already better. But the 400 MM F5.6L surprised me. The IQ is very very good. For a short time I have had the EF 400 F2.8 ISL. The IQ of that lens is out of this world, as is the weight. You need a truck to get where you want to take your photo's.

Light; build-in hood; very nice IQ; nice Bokeh; cheap; 800 euro for a second hand

No IS; F5.6 with extenders makes it F8.0