Focal Lengths: Since it's very hard to get close to most wild animals, wildlife specialists tend to work with long focal lengths. With a 1.5X/1.6X crop factor, the longer superzooms will take the budget-minded APS-C shooter into wildlife territory, as will one of the lower-cost supertele-zooms: 70-300mm, 80-400mm, 100-400mm, 120-400mm, 150-500mm, 200-500mm and the like. The full-frame shooter usually will want at least 400mm, which rules out the superzooms. Note that the lowest-priced 70-300mm zooms (those around $200) don't have the AF performance necessary for wildlife action (they will work well with nonmoving subjects), but the better ones can handle birds in flight and other wildlife action (not as well as the quicker and more accurate autofocusing pro lenses, of course, but better than bargain-basement zooms).
TOP TO BOTTOM: Sigma 120-400mm ƒ/4.5-5.6 DG APO OS HSM; Sony 70-400mm ƒ/4-5.6 G; Nikon AF-S 80-400mm ƒ/4.5-5.6D ED AF VR.
Aperture Requirements: Wildlife photographers often shoot at the lens' maximum aperture to get the fastest possible shutter speed to stop action and to throw the background completely out of focus to place emphasis on the subject (especially important in wildlife portraits). Thus, they prefer the fast pro supertelephotos: 300mm ƒ/2.8, 400mm ƒ/2.8, 500mm ƒ/4, 600mm ƒ/4 and 800mm ƒ/5.6. These lenses are very bulky and costly, but besides lens speed, they offer better image quality, better AF performance, and in the case of the last two, more reach than the lower-cost supertele-zooms.
Lenses for Travel
Focal Lengths: A superzoom is an excellent choice for the travel photographer because it provides the right focal lengths for most travel shots in a single, compact package. While the superzooms generally aren't as good optically as equivalent-priced shorter-range zooms (or prime lenses), they're easy to carry just about anywhere. Having a whole range of focal lengths literally at your fingertips can make the difference between getting and not getting lots of great travel shots.
CLOCKWISE FROM ABOVE: Sigma 24-70mm ƒ/2.8 IF EX DG HSM; Sony Zeiss Vario-Sonnar T* 24-70mm ƒ/2.8 ZA SSM; Tamron 18-270mm F/3.5-6.3 Di II VC PZD; Canon EF 24-70mm ƒ/2.8L IS USM.
Aperture Requirements: A lot of travel photography takes place handheld so you're generally going to lose some sharpness, and you're always going to be pushing at the limits of ISO and shutter speed settings on your DSLR. Plus, travel photography frequently includes night scenes and building interiors. Today's DSLRs provide good performance at higher ISO settings. This can mitigate the need for a superfast maximum aperture, but generally, for travel work, you want to have as much aperture at your disposal as possible. Image stabilization, whether in-camera or in-lens, also helps to offset the slower maximum apertures. Superzooms are relatively slow—ƒ/3.5 at the wide end, ƒ/5.6 or even ƒ/6.3 at the long end. A three-lens zoom kit or primes with fast maximum apertures will give you more latitude to shoot in variable lighting conditions, but fewer options for fast focal-length changes.
If your budget and baggage allotment allow, you can obtain better image quality by carrying the standard three-lens travel kit, which is pretty much the same as the landscape three-lens kit: wide zoom, normal zoom and tele-zoom. While lens speed is of little concern to the landscape shooter, faster lenses can be helpful for travel photography, which is more often done handheld and in dimmer lighting. But three fast lenses are much bulkier (and more costly) than a single superzoom, so consider what's most important to you: optimal image quality or minimal cost and bulk.