Get used to talking in superlatives with the Sigma 300-800 f/5.6 EX APO HSM AF (Street: $6,200), affectionately called the "Sigmonster" by photo enthusiasts.
The Sigmonster is the longest zoom lens for 35mm-based cameras. At 12.9 pounds, it is also the heaviest production lens for 35mm-based photography. At 26 inches long, with lens hood, and a maximum diameter of 6.5 inches, it's not so much big as it is gigantic.
For all of its hugeness, it handles quite well on a sturdy tripod. The tripod collar mounts are well-balanced, and even without a gimbal tripod head, it was easy to pan and maneuver.
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This lens is solidly built and focusing and zooming are both internal, so the lens stays constant in length as you zoom in and out. The zoom collar provides good resistance, but lets you zoom effortlessly from 300mm to 800mm. There is no "zoom slippage" to be seen, even when the lens is pointed at severe angle. The manual focusing collar, closer to the front element, has a big radius, but it is easy to turn in either dedicated manual mode or AF mode for fine-tuning focus.
As expected with a lens of this size, there is a lens strap that attaches to mounting hardware on the tripod collar handle, and to a small dedicated strap collar nearer to the lensmount. Again, as is standard with super-telephoto lenses, there's no giant lens cap to be found. Instead, the lens ships in a well-constructed soft-sided rectangular carrying case with a wide strap for slinging over your shoulder. The included lens hood is just over four inches deep, and, in addition to helping reduce flare, offers a layer of protection to that huge front element.
Even with a camera attached, and the lens hood mounted outwardly, it is not ridiculous to hike a few miles with this Sigmonster. Slung over the shoulder, it actually hangs quite well for such a big piece of machinery.
At 300mm, the f/5.6 maximum aperture and close-focusing distance of just under 20 feet is nothing to write home about. There are plenty of smaller and faster 300mm lenses on the market, but really, no one is buying this lens for its 300mm characteristics. The real selling point is the portability of this 300-800mm f/5.6 zoom monster.
A 300mm f/5.6 that close focuses to just about 20 feet? Nothing special...
An 800mm f/5.6 that close focuses to just about 20 feet? Now that's something else!
And throw in all those other millimeters between 300 and 800, and you've got yourself a pretty amazing piece of optical engineering.