Pro mid-range zooms generally have a fixed aperture, usually ƒ/2.8 or ƒ/4. The variable-aperture zooms in this focal-length range are commonly consumer kit lenses—good, but not pro-level performers.
The fast zooms—ƒ/2.8 and ƒ/2—are better suited for dim-light work than slower ƒ/4 lenses. The fast lenses can also produce more limited depth of field to throw the background really out of focus and concentrate the viewer’s attention on a specific portion of the subject. Generally, the bokeh—background and foreground blur—is more pleasant with the faster lenses, too.
On the other hand, the ƒ/4 zooms are compact, making them easier to carry, and the slower zooms cost less. If you don’t need the benefits of the faster lens like low-light capability and extremely limited depth of field, you’ll probably be better off with the slower option. And, by and large, the ƒ/4 zooms are sharper at ƒ/4 than the faster zooms are at ƒ/2.8.
Note that the effective angle of view isn’t the only thing that changes when you switch camera sensor sizes. The depth of field produced by a given aperture also changes. A 12mm ƒ/2.8 lens on an MFT camera provides the field of view and depth of field of a 16mm ƒ/4 lens on an APS-C camera and a 24mm ƒ/5.6 on a full-frame camera when focused at the same distance, providing the same framing and perspective. That’s why you should go with full frame if you like those extremely limited depth-of-field effects. To get the depth of field a 24mm lens provides at ƒ/2.8 on a full-frame camera with equivalent framing, you’d need a 12mm ƒ/1.4 lens on an MFT camera—and there aren’t any of those. Of course, if extremely limited depth of field isn’t important in your work, this won’t be a consideration.
Zoom lenses offer several advantages over a set of prime lenses covering the same range of focal lengths. First, obviously, are cost and bulk. It costs less to buy one zoom than several primes, and it’s easier to carry the one zoom around than a bag full of primes. The zoom also allows you to quickly reframe with the twist of a wrist, rather than having to physically remove one lens and attach another each time you want to frame tighter or more loosely. And, of course, minimizing the number of lens changes helps keep your sensor free of dust. 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.
While apparently a full-frame model is coming, all of Pentax’s DSLRs so far have been APS-C cameras. Pentax offers a pair of pro mid-range zooms designed specifically for the APS-C sensors. The flagship DA* 16-50mm ƒ/2.8 ED AL (IF) SDM features rugged weather-resistant constructio
n, and two ED plus three aspherical elements to combat aberrations and optimize image quality. The DA 17-70mm ƒ/4 AL (IF) SDM is only 2.8 ounces lighter, but adds 20mm to the long end (equivalent to 25.5-105mm on a full-frame camera vs. 24-75mm for the 16-50mm) and costs about half as much.
Samsung’s pro mid-range zoom is the NX 16-50mm ƒ/2.8 ED OIS for its APS-C mirrorless cameras. It features an ƒ/2.0 aperture at the wide end for full-frame-style minimal depth of field. A Ultra-Precise Stepping Motor provides quick, quiet AF, and Optical Image Stabilization minimizes the effects of handheld camera shake. Three aspherical, two ED and two XHR elements minimize aberrations, maximize performance and make for a more compact lens.
Sigma made its name as a lensmaker before getting into the camera business, and offers a wide range of lenses for both its own cameras and other popular brands. For full-frame DSLRs (and film SLRs), the 24-70mm ƒ/2.8 IF EX DG HSM features three ELD and two SLD elements to minimize aberrations, costs significantly less than other 24-70mm ƒ/2.8 lenses currently on the market and is available in mounts for Canon, Nikon, Pentax, Sigma and Sony DSLRs. The 24-105mm ƒ/4 DG (OS) HSM / A is a stop slower, but adds 50% to the long end of the focal-length range and is a member of Sigma’s much lauded Art lens family. It’s available in mounts for Canon, Nikon, Sigma and Sony DSLRs. For APS-C cameras, Sigma offers the 17-50mm ƒ/2.8 EX DC (OS) HSM, with two FLD elements (equal in performance to very costly fluorite), three aspherical elements and a focal-length range equivalent to 25.5-75mm on a full-frame camera. Sigma’s OS is available in Canon, Nikon and Sigma mounts, but not Pentax and Sony mounts (Pentax and Sony DSLRs have built-in sensor-shift stabilization that works with all lenses).
Sony’s flagship Vario-Sonnar T* 24-70mm ƒ/2.8 ZA SSM features a Carl Zeiss design, ED and aspherical elements, and an SSM Supersonic Wave AF Motor for quick, quiet autofocusing. The 28-75mm ƒ/2.8 SAM offers four aspherical elements and Sony’s SAM Smooth Autofocus Motor for about half the 24-70mm’s price. Both are full-frame lenses. For APS-C, Sony offers the DT 16-50mm ƒ/2.8 SSM, with ED and aspherical elements and SSM motor. Sony also makes mirrorless cameras, and offers constant-aperture mid-range zooms for them. For the full-frame a7-series cameras, there’s the Vario-Sonnar T* FE 24-70mm ƒ/4 ZA OSS, with Zeiss design, five aspherical elements and one ED element, and Sony’s Optical SteadyShot image stabilization, as well as the FE PZ 28-135mm ƒ/4 G OSS, with quiet power zooming. For Sony’s APS-C mirrorless cameras, there are two choices. The E Vario-Tessar T* 16-70mm ƒ/4 ZA OSS is a Zeiss design with Sony OSS stabilization, while the E PZ 18-105mm ƒ/4F OSS features Handycam-level power zooming for video and Sony’s OSS stabilization.
Tamron offers two ƒ/2.8 mid-range zooms for full-frame DSLRs and two for APS-C. The SP 24-70mm ƒ/2.8 Di VC USD features Tamron’s proprietary tri-axial Vibration Compensation and an Ultrasonic Silent Drive AF motor for quick, quiet autofocusing. Two XR (Extra Refractive Index) elements bend light more sharply to minimize aberrations and allow for more compact lenses, while three ED (Extra-low Dispersion) elements minimize chromatic aberrations. The SP 28-75mm ƒ/2.8 XR Di features XR, LD and aspherical elements to provide a high-performance, lower-cost alternative. For APS-C, there’s the SP 17-50mm ƒ/2.8 XR Di II VC with Vibration Compensation and XR, LD and aspherical elements, as well as the SP 17-50mm ƒ/2.8 XR Di II, without the VC, at a lower cost. All four are available in mounts for Canon and Nikon DSLRs, the SP 24-70mm also for Sony, and the SP 28-75mm and SP 17-50mm non-VC also for Pentax and Sony.
Tokina has a new AT-X 24-70mm ƒ/2.8 Pro FX lens for full-frame DSLRs in the works, but no further information was available at press time.