Canon EF 100-400mm f/4.5-5.6L IS II USM

It is dawn at a marsh, your tripod legs are sinking into the mud, and a heron lifts off forty meters out. The white barrel comes up, the ring slides from 100 to 400 in one twist, and the shot is yours before the bird clears the reeds. Canon shipped this Mark II in 2014 to replace the 1998 original, the push-pull "trombone" version that birders had complained about for the better part of two decades. The new one zooms with a rotating ring, the way most people expect a zoom to work, and it does not pump dust toward the sensor every time you reach for length.

Optically this is the cleanest the 100-400 has ever been. Wide open at 400mm and f/5.6 it is already sharp in the center, which matters because that is exactly where you live when something has feathers. Stop down to f/8 and the corners come up for landscape work. The fluorite and Super UD elements keep chromatic aberration off the high-contrast edges that wreck telephoto images: a backlit branch, a gull against bright sky. Contrast runs high, a touch punchy, and color sits warm in the usual Canon way. Flare is well controlled, helped by the deep hood, though shooting straight into a low sun will still wash the frame.

The Image Stabilizer is the real argument for owning it. Canon rates it at four stops, and it gives you the panning options that telephoto work needs. Mode 2 detects a pan and stabilizes only the cross-pan axis, so following a banking aircraft stays smooth. Mode 3 holds correction off until the instant of exposure, which keeps the viewfinder from fighting you while you track. On a film body with no in-body stabilization, that is the difference between a usable frame at 1/125 and a smear. Picture an EOS-1V loaded with Tri-X, handheld at 400mm: the IS is doing work no other part of the kit can.

Who reaches for it is no mystery. Wildlife and bird shooters, the air-show and motorsport crowd, and landscape photographers who like to compress distant ridgelines into stacked planes. It is the lens that lives in the bag of anyone who shoots subjects they cannot walk up to. The downside is the variable aperture. By 400mm you are at f/5.6, and in forest shade or last light that costs you shutter speed you often cannot spare. It is also not a macro despite the 0.31x magnification people like to cite; it is a reach lens that happens to focus reasonably near.

The metering note is the filter thread. At 77mm you can stack a polarizer for glare off water and wet plumage, or a graduated ND for those compressed-horizon landscapes. Meter through the filter, or set the filter's exposure factor in Zone Light Meter so a two-stop polarizer does not leave your sky a stop and a half under. Against the Sigma and Tamron 150-600 superzooms, the Canon gives up reach but is generally regarded as faster-focusing and better-built, with resale that has held up, which is why working shooters keep buying it used.