Canon EF 500mm f/4L IS USM

A superb lens, fantastically sharp, nice contrast, great focusing speed, very robust (able to take some knocks, though best avoided if possible!), great full-time manual focusing - very smooth, when not hindered (see below). Great with the Canon 1.4x tele-converter, focusing speed still great, etc. Lovely!!! Stick a "Wildlife Watching Supplies" neoprene hood cover on, helps protect from knocks, and breaks up the "white".

Sharp, nice contrast, fast, robust - just plain gorgeous

More of a niggle really, when shooting on a bean bag (or 3) from the window/top of a , it can be difficult to manually focus, as the focussing ring tends to sit on the edge of the bag. I need to experiment more with various bag set-ups to get it right.

Canon 300mm F4 IS USM

Not needed yet, or on most of my Canon gear.

This is a fabulously sharp and very versatile lens for wildlife photography (I use it mainly for birds). Works extremely well with the Canon 1.4X TC and the 2X TC (there is a small but noticable loss of sharpness with the latter, but the lens is so good that even with the 2X TC the images can be stunningly detailed). The IS works extremely well even with converters attached, and despite some ambiguity in the instruction manual, it's highly recommended in all conditions -- even with the lens on a tripod (a gimbal mount is highly recommended, by the way -- I use a Wimberly Sidekick). Closest focus is 14 feet, which is OK for small birds with a 1.4 or 2X TC, but nowhere near enough for the basic lens. However, the autofocus is fast, silent, and reliable. It works superbly even with extension tubes attached. Have done enough with the 'AI Servo' tracking autofocus mode (EOS 1V) to realize how valuable this feature is for taking photos of moving targets (like swimming ducks or grebes). Many nature photographers debate between this lens and the Canon 600 f4 (the same debate affects Nikon users, I'm sure). There are times when the additional 100 mm of reach of the 600 would be valuable, but in my judgment the 500 is a more useful lens for most purposes because of its lower cost, smaller size (and weight!), and closer minimum focus.

optical and construction quality, fast and decisive autofocus, IS. Wished it focused closer -- a complaint pertinent to nearly all big telephotos. Small enough to fit in a carry-on backpack that will get through current airline size regulations (but definitely not tiny!). Pricey but worth it.

It's a bit heavy (comes with the territory of a 500 mm f4), and awkward to maneuver with the hood attached. Placement of the focus lock buttons is abysmally clumsy -- way out near the front of the lens. They're very hard to use without pushing the lens off target, even with a sturdy tripod. Switches are a little exposed and can be inadvertently set to something you don't want. "White" finish is vulnerable to scratching. The JRF neoprene camo lens covers are a good idea if you take this into the field -- not so much for concealment as for protecting the lens from blemishes.

Sigma 800 f5.6, various 400 mm lenses, old Leitz 560 mm f5.6

haven't had to use it and hope not to.

As an outdoor photographer specialising in bird photography I would say an absolute must to have this lens. Even having a good price it pays off in higher rate of good photos. Using it with the 2X converter you get a 1000mm f8. Asuming what Canon says that you win 2 stops due to the IS you have a 1000mm f4. I hve used this lens as described with a 2+ pushed 100asa film and got excellent results.

Sturdy built. Lightweight compared to others. Superb sharpness and contrast even when used with original 1.4X and 2X converters

Same as at the 300mm IS. The switches can be turned easily by accident into another position

Canon 300mm f2.8 L IS USM

Good