The zoom also allows you to set intermediate focal lengths—if you have 24mm, 35mm, 50mm and 70mm prime lenses, but 43mm would be just perfect for the shot you have in mind, the zooms let you go there and the primes don’t. Sure, you could just move in a bit with the 35mm prime or back up a bit with the 50mm, but that also changes perspective. Moving closer than the ideal distance for the shot you have in mind will expand perspective, not always a desired effect. And moving farther away will compress perspective, also not always desirable. The distances in this example aren’t that big a deal, but the point is, a zoom lens gives you more compositional flexibility than a set of primes.
Of course, you can’t beat a pro-level prime lens for sharpness. It’s also easier to correct all the aberrations that can affect a lens at a single focal length than for a range of them. But today’s pro zooms are very good optically, and many top professionals use them regularly.
Mid-range zooms go from wide-angle to telephoto, and so incorporate a variety of special elements to optimize performance. Low-dispersion (and extra-low-dispersion) elements minimize chromatic aberrations. Aspherical elements minimize spherical aberrations and distortion. High-refractive-index elements minimize aberrations and make for more compact designs, as they bend light more sharply than conventional elements. The presence of these elements doesn’t guarantee an excellent lens, but their absence probably indicates a non-excellent one.
Canon offers three pro full-frame mid-range zooms and one APS-C one. The EF 24-70mm ƒ/2.8L IS II USM is the flagship model, rugged and weather- and dust-sealed, with one Super UD and two UD elements to minimize chromatic aberrations and two types of aspherical elements to minimize spherical aberrations. If you don’t need that ƒ/2.8 maximum aperture, you can save 7.4 ounces and $1,000 with the EF 24-70mm ƒ/4L IS USM, which features a macro mode that takes you as close as 0.7X magnification. The EF 24-105mm ƒ/4L USM gives you more focal length at the long end for those who like tighter headshots with still pleasing perspective (but lacks the IS stabilization). If you have an APS-C Canon DSLR, the EF-S 17-55mm ƒ/2.8 IS USM gives you a pro-quality lens with focal lengths equivalent to 27-88mm on a full-frame camera.
Nikon’s extensive lens lineup includes three pro mid-range zooms—two full-frame ones and a DX model designed for APS-C DSLRs. The flagship AF-S Nikkor 24-70mm ƒ/2.8G ED features three ED elements and three aspherical elements to correct aberrations and optimize image quality, even wide open at ƒ/2.8, along with pro-grade dust and moisture resistance. If you don’t need the ƒ/2.8 maximum aperture, you can gain 35mm on the long end, plus vibration reduction (VR), with the AF-S Nikkor 24-120mm ƒ/4G ED VR, and save $600 in the bargain. For APS-C users, Nikon offers the AF-S DX Zoom-Nikkor 17-55mm ƒ/2.8G IF-ED, featuring three ED and three aspherical elements like the 24-70mm and providing focal lengths equivalent to 25.5-82.5mm on a full-frame camera.
Olympus offers the M.Zuiko ED 12-40mm ƒ/2.8 PRO zoom for Micro Four Thirds cameras (equivalent in field of view to 24-80mm on a full-frame camera). It features two aspherical, ED and HR (High Refractive) elements each and one aspherical ED, DSA and HD element each among its 14 in 9 groups, and is splash-, dust- and freeze-proof. MSC provides near-silent autofocusing.
Panasonic’s LUMIX G X Vario 12-35mm ƒ/2.8 for Micro Four Thirds cameras features four aspherical elements to control spherical aberrations and distortion, an Ultra ED element to counter chromatic aberrations and an Ultra HR (High Refraction) element for corner-to-corner sharpness. The lens is sealed against moisture and dust, and features Power O.I.S. optical image stabilization with near-silent operation for still shooting and movies.