This is by far my most used telephoto lens for a lot of reasons. It offers excellent focal length for bird photography, especially when coupled with the EF 1.4x II or III. Optically the lens is nothing short of fantastic even with the 1.4x TC. The IS works great and is certainly useful in low-light situations.

I find the lens to be light enough to hand-hold and hike around with. The size is also small enough to shoot from the car conveniently. I can usually drive around with the lens sitting in my lap so I can quickly point it out the window for grab shots when doing roadside birding. The size of the lens is also convenient for traveling by air. I feel much more comfortable travelling with the 500mm f/4 than I do with my 600mm f/4 or 400mm f/2.8.

The minimum focus distance I short enough to that the lens is great for small warblers and sparrows. Another nice feature is the three position focus limiter which means that you can restrict the focus not only to distant subjects (great for photographing flying birds) but also to close subjects which is great for photographing small birds as they forage at close range.

The AF stop buttons are near the end of the lens barrel. This makes them very handy since holding the lens to use the buttons also means that you have your hand under the weight at the end of the lens. Holding the lens this way helps to make the lens steady when shooting hand-held. When using the 500 I also find it useful to customize the AF stop buttons so that they toggle between Ai-servo and One Shot AF modes.

AF preset is another great function available on the 500mm f/4L IS USM. I typically use this feature when watching water features or hummingbird feeders. I can set the focus on a perch near the water feature or at the port on the hummingbird feeder. I can continue to photograph birds in the vicinity and when a bird approaches the feeder I can rotate the switch on the lens barrel and instantly the focus is right at the feeder were I had pre-set it.

Aside from the price of this lens there really is very little fault that I can find with it and considering how much use I have personally gotten from the lens even the price isn’t so terrible.