Lenses with long zoom ratios are popular with travelers who don't want to carry a lot of gear, and photographers who simply want to enjoy the benefits of an SLR without having to make frequent lens changes. There are always optical compromises necessary to design a lens with such a long zoom range, and the Nikon AF-S DX Nikkor 18-300mm f/3.5-5.6G ED VR ($999.95) does exhibit noticeable distortion and some softness toward the edges of the frame. But overall it's a strong performer, capturing detailed images from 18 to 300mm, and improving around the edges when stopped down. It's priced on the high side, carrying a premium when compared with the Nikon AF-S DX Nikkor 18-300mm f/3.5-6.3G ED VR ($699.95) and the Sigma 18-300mm F3.5-6.3 DC Macro OS HSM Contemporary ($398.20 at Amazon) , but if you're set on getting an all-in-one zoom, know that the Nikkor 18-300mm f/3.5-5.6G is one of the best bets in its class.

Design
The 18-300mm is a hefty lens. When set to the 18mm position it measures 4.7 by 3.3 inches (HD), and just about doubles in height when set to 300mm. The front element is on the large side, and accepts 77mm front filters. A reversible petal-style lens hood is included, as is a soft carrying case and standard front and rear caps.

Construction is a mix of metal and polycarbonate, with the outer barrel including both materials. The telescoping mechanism that extends while zooming includes outer and inner barrels; the former is metal and the latter polycarbonate. The metal elements, and the amount of glass needed to maintain image quality in a lens with such a long zoom ratio, account for its 1.8-pound weight.

The lens is designed for use with APS-C cameras from Nikon, and as such it bears the DX designation. When paired with a DX SLR, like the D3300 ($586.98 at Amazon) or D5500, it covers a field of view that's equivalent to a 27-450mm zoom on a full-frame body. You can also use it with a full-frame (FX) Nikon like the D610 in DX mode, which crops images to match the format of the smaller APS-C image sensor. Doing so limits the capture resolution, but if you move from a DX to an FX body, the lens won't be worthless.

Both the manual focus ring and the zoom ring are covered in textured rubber. The focus ring sits toward the base of the lens, while the zoom control rests right behind the front element. It has markings at 18, 28, 50, 105, 200, and 300mm. There's a locking switch that can keep the lens set to its 18mm position, which prevents the lens extending.

Other toggle switches control the 3.5-stop Vibration Reduction (VR) stabilization system. One switch turns it on or off, and another changes between Normal and Active modes. You'll want to use the latter when shooting from a moving vehicle or similarly unstable platform. A third switch controls the focus mode—the M/A position sets the lens to autofocus, but allows full-time manual override, while M is there for pure manual focus.

Focus can be locked as close as 1.48 feet (0.45 meter) as measured from your camera's image sensor. This close focus distance is constant throughout the zoom range, which means that you can capture photos at about one-third life-size (1:3 magnification) at 300mm. The 18-300mm isn't a true macro lens, a designation that requires the lens to reproduce items sans distortion, but the close focus capability certainly makes it a versatile tool. The Sigma 18-300mm also supports 1:3 magnification at its closest focus distance and 300mm setting.

Image Quality
I tested the 18-300mm with the 20.9-megapixel D500 ($1,496.95 at Amazon) . At 18mm f/3.5 the lens scores 2,587 lines per picture height on Imatest's standard center-weighted sharpness test. Image quality is strongest in the center, approaching 3,000 lines, and tapers off as you approach the edges of the frame. But the outer third still manages a strong 2,178-line score. Narrowing the aperture to f/4 doesn't have a huge effect on image quality—the lens resolves 2,612 lines there. It maintains a score of about 2,500 lines at narrower apertures through f/11, but drops to 2,189 lines at f/16 and a meager 1,570 lines at f/22. As with most lenses, you should try to avoid very narrow apertures, as they introduce diffraction, which detracts from sharpness.

Image quality remains strong at 50mm, but be aware that the maximum aperture narrows quickly. The lens loses more than half of its maximum light-gathering capability at 50mm, a focal length at which it opens to just f/5.3. It does show strong sharpness here, however, scoring 2,723 lines on the center-weighted test, with good performance at the outer third of the frame (2,306 lines). There's a slight bump at f/5.6 and f/8—about 2,800 lines at both settings—before diffraction cuts into image quality at f/11 (2,560 lines), f/16 (2,137 lines), and f/22 (1,491 lines).

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The edges of the frame appear softer at 100mm. At f/5.6 the center-weighted score remains excellent (2,493 lines), but the outer third of the frame drops to 1,765 lines. Stopping down to f/8 improves the edge quality significantly, to 2,230 lines, and bumps the average score to 2,688 lines. As expected, there's a slight hit in fidelity at f/11 (2,491 lines) and more significant drops at f/16 (2,031 lines) and f/22 (1,480 lines).

The overall score is solid at 150mm f/5.6—2,289 lines—but edges take a noticeable hit, dropping to 1,375 lines. Stopping down to f/8 improves the periphery (1,852 lines) and the overall score (2,256 lines at its peak). The best performance from edge to edge, however, is at f/11—the average score does drop to 2,472 lines, but edges improve to 2,221 lines. You should avoid shooting at f/16 (2,112 lines) and f/22 (1,564 lines) if possible.

At 200mm f/5.6 the lens is a solid performer through most of the frame, averaging 2,305 lines, and edges are soft, but not muddy (1,629 lines). Stopping down to f/8 nets improvements; the average score jumps to 2,490 lines, and edges cross the 1,800-line mark. Once again, f/11 gets you the best performance at the edges (2,182 lines), with a solid overall score (2,428 lines). Image quality isn't as good at f/16 (2,102 lines) and f/22 (1,594 lines).

Performance remains strong when the lens is set to 300mm. At f/5.6 the average score is 2,122 lines. Edge quality is weaker here—1,582 lines. Stopping down to f/8 offers modest edge improvement (1,693 lines) and a strong center-weighted average (2,352 lines). Peak image quality is achieved at f/11—the overall score is 2,365 lines and edges show 2,071 lines. There's a dip at f/16 (2,108 lines) and a significant drop at f/22 (1,592 lines).

Despite showing some softness along the edges at wide apertures, the Nikkor 18-300mm is a better, more consistent performer than the competing Sigma 18-300mm Contemporary. The Sigma lens can't put up the numbers that the Nikkor does. At its best, the Contemporary shows around 2,200 lines, but dips well below that mark at times.

Distortion is a fact of life with a long zoom design. At 18mm the lens shows significant barrel distortion, about 5 percent, which causes straight lines to be drawn with a noticeable outward curve. It quickly gives way to pincushion distortion, which gives the same lines the appearance of an inward curve. There's about 2 percent at 50mm, 2.5 percent at 100mm, 150mm, and 200mm, and 2 percent at 300mm. If you shoot JPGs you can set your Nikon SLR to correct the distortion automatically, and Raw shooters can easily remedy the issue via a profile correction in Lightroom ($9.99/Month at Adobe) .

Imatest also checks for even illumination. Lenses often shed less light at the sides and corners of the frame than at the center, which can be analyzed with a tool like the ExpoDisc, which covers the lens to capture a uniform white frame, and Imatest's Uniformity tool. At 18mm f/3.5 and f/4 the corners lag behind the center by about 2 stops (-2EV). Narrowing the aperture to f/5.6 cuts that differential to -1.2EV, and at f/8 the corners lag behind the center by about 1EV. Illumination at the sides of the frame is within the 1EV we look for in an image from f/4 onward.

Illumination is more even when zoomed. At 50mm and 100mm the sides and corners are quite close to the center in brightness. Corners show a -1EV differential at 150mm, 200mm, and 300mm f/5.6, but stopping down to f/8 rectifies this. Overall these are solid results from a long zoom lens. And again, JPG shooters can enable peripheral illumination correction to compensate, and the same Lightroom profile that removes distortion from Raw images also corrects for Uniformity.

Conclusions
A lens with a 16.7x zoom ratio is never going to deliver the same performance as a top-end prime lens or a shorter zoom. The Nikon AF-S DX Nikkor 18-300mm f/3.5-5.6G ED VR offers consistent sharpness throughout its zoom range, and while it does show significant distortion, it's easily remedied via an in-camera correction or Raw conversion software. It's one of the better long zoom designs we've seen, delivering better performance than similar lenses that undercut it in price. If you're a Nikon owner who is serious about an all-in-one zoom, and want to minimize compromises in image quality, spending the money on this lens is worth it.

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