If there was an official lens of OP, it would be the wide-angle zoom. Take a look through the submissions to our Assignments galleries, contest galleries and the pages of the magazine, and you'll quickly notice how often the wide-angle focal length gets the call among nature photographers. The wide-angle zoom gives you framing and perspective options in that 16mm and 17mm to 35-40mm range (we're talking about full-frame DSLRs here). This is the range that lets you capture dramatic mountain vistas, cloudscapes, evocative near-far David Muench-style compositions and more. These lenses are available for full-frame, APS-C and Micro Four Thirds cameras in focal lengths that provide angles of view as wide as 114º to 122°, and you can change cropping instantly with the twist of a wrist—no need to fumble around and expose the sensor to the elements.
To find the best wide-angle zoom for your style and budget, we've broken down the key specifications and design elements. And we've created a comprehensive chart of what's available today in terms of wide-angle zooms for full-frame, APS-C and Micro Four Thirds cameras.
There are two basic wide-angle lens designs: symmetrical and retrofocus. DSLR and SLR lenses are retrofocus types because symmetrical designs would intrude too far into the camera body, interfering with the operation of the SLR mirror. Mirrorless cameras, with no mirror and a much shorter flange-back distance (the distance between the lens mount and the image plane), can use either type—in fact, pretty much any lens for which an adapter can be found.
For either type of lens, multiple elements are used to minimize aberrations and optimize performance. Lens design has come a long way in a relatively short time with the development of computer-aided design, which allows designers to see the results of various element combinations quickly, where in the pre-computer days, the manual calculations took much longer. Aspherical elements, whose curves vary from center to edges, eliminate or greatly reduce spherical aberrations and distortion, which especially affect very fast, very wide-angle lenses. Aspherical elements also help keep size down in wide-angle zoom lenses. Modern manufacturing processes make it possible to produce quality aspherical elements affordably.
Inside A Modern Zoom
The faster the lens (i.e., the larger its maximum aperture), the better off you are in low-light situations. With a faster lens, you can use a faster shutter speed (to minimize the effects of camera shake and subject motion) or a lower ISO setting (to maximize image quality) in a given light level, and the viewfinder image in a DSLR will be brighter for easier composing and manual focusing. (Note that using Live View mode with a tripod-mounted camera can make for easier manual focusing with any lens.) But faster lenses tend to be bulkier and more costly than slower ones, and faster lenses aren't always "better." Some have found, for example, that Canon's 16-35mm ƒ/4 zoom is actually sharper than their 16-35mm ƒ/2.8 (besides being lighter and less costly). If you need ƒ/2.8 (for selective-focus compositions or low-light situations), you need ƒ/2.8, but if you don't, you can save some money and bulk by going for a slower lens without losing image quality.
Variable Vs. Constant Aperture
Some zoom lenses maintain a constant ƒ-number throughout their zoom range. A 16-35mm ƒ/2.8, for example, has a maximum aperture of ƒ/2.8 at all focal lengths. With others, the maximum aperture gets smaller as you zoom from wide to longer focal lengths. A 12-24mm ƒ/4.5-5.6, for example, has a maximum aperture of ƒ/4.5 at 12mm and a maximum aperture of ƒ/5.6 at 24mm. This isn't a big deal with superwide zooms, as we're interested in the wide end where the aperture is fastest (it's more of a concern for supertelephoto zooms where you'll be using mostly the longer, slower focal lengths). But there are some things to keep in mind. Constant-aperture zooms tend to be faster and of better quality (and more costly) than the variable-aperture lenses. And the variable-aperture zooms change focus as they're zoomed; the constant-aperture lenses are more likely to be true zooms, which maintain focus when zoomed. AF systems will compensate for focus shifts automatically, and TTL metering will adjust for the changing apertures automatically as variable-aperture lenses are zoomed, but you'll have to compensate manually if using manual focus or a handheld meter.
At wide apertures, various aberrations reduce a lens' sharpness, and at small apertures, diffraction reduces sharpness. Each lens has a "sweet spot" aperture at which it produces sharpest results. Generally, this is a stop or two down from wide open, but if maximum resolution is crucial, it's a good idea to test your specific lens(es) to find the sharpest aperture setting(s). Keep in mind photo considerations, however. If you're doing a selective-focus shot to keep the viewer's attention on a specific portion of a subject, you'll want to shoot wide open to minimize depth of field; and if you need a lot of depth of field to get important foreground and background subjects sharp, you'll need to stop down.
Minimum Focusing Distance
One popular wide-angle effect is created by moving very close to a foreground object to make it large in the frame and using the zoom's wide angle to still show enough of the surroundings for an effective composition. The closer the lens' minimum focusing distance, the more pronounced this effect can be, because the closer you move to the nearby subject, the greater the perspective expansion. All of the zooms in our chart will focus down to one foot or less, so all can do this effect quite well.
A given lens, set at a given focal length and focusing distance, projects a given image on the focal plane (film or image sensor). This image doesn't change because you put a larger or smaller piece of film, or a larger or smaller image sensor, at the focal plane.
A smaller sensor just crops into the full image projected by the lens, reducing the angle of view and increasing the size in the image frame of everything in the scene. This isn't an increase in actual magnification; the subject's image at the image plane remains the same. But the tighter cropping makes the subject fill more of the frame while reducing the field of view.
This was significant in the early days of digital SLRs because those cameras had APS-C sensors that were smaller than a 35mm film frame. So lenses produce a smaller field of view on the digital SLRs than on 35mm SLRs. A 24mm used on an APS-C camera produces the framing of a 36mm lens used on a 35mm SLR. And the first DSLRs were based on film SLRs and used the same lenses, so you couldn't go as wide with the DSLRs and with the film cameras photographers were used to.
Today, this isn't a big problem. There are quite a few full-frame DSLRs with sensors that are the same size as a 35mm film frame, so there's no crop factor. A lens used on a full-frame DSLR frames just like it does when used on a 35mm film SLR. There also are a number of really short-focal-length zooms designed specifically for APS-C sensors, so we can do wide-angle work as well with these cameras as with full-frame models. A few superwide zooms for Micro Four Thirds cameras even provide the same field of view as the wide zooms for APS-C and full-frame cameras.
You'll note in the accompanying chart that the superwide zooms produce an angle of view of around 100º-115° at the wide end, but this means wide-end focal lengths of 12-18mm for full-frame lenses, 8-12mm for APS-C lenses and 7-9mm for Micro Four Thirds lenses.
Vignetting is a darkening of the image at the edges and corners. The image projected by any lens is brightest in the center and dims as you move away from the center. But the effect is most apparent with wide-angle lenses. The wider angle of view can also "see" the rim of a too-thick filter (or stack of filters) mounted on the lens. Stopping the lens down can reduce optical vignetting, while using a thin filter (and only one filter) can minimize that vignetting. All wide-angle lenses exhibit some vignetting; modern designs tend to minimize it. Some cameras offer in-camera vignetting correction (some call it peripheral illumination correction), and you can also compensate in postprocessing.
Chromatic aberrations are most evident in supertelephoto lenses, but can affect shorter lenses, too, especially zooms. Manufacturers employ low-dispersion elements to minimize chromatic aberrations, and better wide-angle zooms include some. These elements have designations such as ED, UD, LD, and SD. Fluorite (and FLD) elements are especially effective in reducing chromatic aberrations.
Different focal lengths create different aberration problems, so zoom lenses require more elements than prime (single-focal-length) lenses to offset them (an element that makes this aberration better might make that one worse). This tends to make zooms bulkier than primes (but far less bulky than several primes, which would be needed to provide the same range of focal lengths). But modern technology—computer-aided design, and new element materials and shapes—provides us with some excellent wide-angle zooms that aren't unwieldy.
Some cameras can compensate automatically for lens aberrations, vignetting and even diffraction when the camera manufacturer's lenses are used. Distortion, vignetting and chromatic aberrations can also be corrected in postprocessing using the camera manufacturer's software or popular image-editing programs like Adobe Photoshop and Lightroom.
| Do-It-All Zooms
There are a number of "do-it-all" zooms for full-frame and 35mm cameras, and a greater number for APS-C cameras, that go from wide-angle (28mm for full-frame, 18mm for APS-C) out to 200mm or even 300mm. Tamron even offers the 16-300mm ƒ/3.5-6.3 Di II VC PZD for APS-C, which provides full-frame-equivalent focal lengths of 24-450mm. These lenses are great when you want to carry just one lens or avoid lens changes (and the resulting dust on the image sensor assembly) in harsh conditions. But because of their wide range of focal lengths, their designs must contain compromises that result in less optimal performance at the wide setting than prime (single-focal-length) or shorter-range zooms that start at 16mm or 18mm. And, of course, 16mm is as wide as they go, while you can get shorter-range APS-C zooms that start as wide as 10mm. So, if you want to carry just one lens to handle everything, the all-in-one zooms are terrific, but if you specialize in wide-angle work, the shorter-range superwide zooms are better choices (and are also less bulky).