Specific image quality issues
As always, our studio tests are backed up by taking hundreds of photographs with the lens across a range of subjects, and examining them in detail. This allows us to confirm our studio observations, and identify any other issues which don't show up in the tests. The Nikon 18-300mm turned out to be a reasonably good performer in good light, although rather weak at the long end of the zoom.
The 18-300mm has a pretty complex optical design, and as might be expected, this can cause problems with flare at times. It's reasonably well-behaved when the sun is in the frame at wideangle; as always you'll get a diagonal pattern of multicoloured internal reflections, but contrast holds up OK. The 9-bladed diaphragm results in 18-armed 'sun stars' if you stop down far enough to make this effect visible.
|18mm, F22, sun in frame||52mm, F16, sun just outside frame|
The bigger problem, shown in the second example, is what happens when pointing the lens into the light with the sun outside the frame, where you'll see significant veiling and loss of contrast. In this case, though, the effect isn't entirely malign - it also has the effect of lifting the shadows and making details more visible.
Background blur ('bokeh')
One genuinely desirable, but difficult to measure aspect of a lens's performance is the ability to deliver smoothly blurred out-of-focus regions when trying to isolate a subject from the background, generally when using a long focal length and large aperture. This lens can allow you to achieve quite substantially blurred backgrounds, especially at longer focal lengths and large apertures.
The 18-300mm, like most superzooms, isn't especially wonderful at rendering distant backgrounds, which tend to look a little 'busy' and hard-edged. But in the grand scheme of things, it's not hugely objectionable either. When used for close-ups, though, it generally gives attractively-blurred backgrounds that complement the subject nicely.
|300mm F5.6, Nikon D3200||120mm F5.6, Nikon D3200|
|Background, upper left||Detail, lower right|
The 18-300mm shows moderate lateral chromatic aberration at wideangle, along with significant yellow/blue fringing in the middle of its range (~50mm). Most recent Nikon DSLRs dating back to the D300 will automatically correct this in their JPEG output (although not the entry-level models), so a lot of users will never notice. But it won't necessarily be corrected automatically if you shoot RAW, although most modern processors have effective CA removal routines built-in (including Nikon's own software).
The example below gives an idea of what you can expect at 18mm, where CA tends to be most obvious. There's visible red/magenta fringing across much of the frame, turning to green/magenta in the extreme corners. But overall it's not too objectionable.
|100% crop, top left|
|18mm F8, Nikon D3200||100% crop, upper centre|
Distortion and distortion correction
Typically for a superzoom, the 18-300mm shows extreme distortion at almost all focal lengths, with strong barrel distortion at wideangle quickly giving way to pincushion distortion across the majority of the zoom range. Recent Nikon SLRs can (in principle) correct this automatically, either while shooting or using the Retouch menu in playback. Note though that the camera may well need to be updated with the latest 'Distortion control data' file for this to work properly (which is available to download from Nikon's websites).
The rollover below shows how the distortion looks in practice, comparing uncorrected camera JPEGs with versions of the same file corrected in-camera and using Photoshop's 'Lens Correction' module. The barrel distortion at 18mm is severe, and visually unattractive with this kind of geometric composition. The camera doesn't correct it fully using the Retouch menu option (even with the adjustment slider set to maximum correction), leaving vertical lines towards the edge of the frame noticeably bent. In contrast, the pincushion distortion is corrected completely.
18mm corrected in-camera
18mm corrected in PS
68mm corrected in-camera
68mm corrected in PS
*Adjustment parameters = +5 for barrel distortion at 18mm, -3 for pincushion distortion at 68mm
Softness at telephoto
The 18-300mm's main selling point is its long telephoto end - the longest of any superzoom to date. It's also distinguished by the fact that it maintains a maximum aperture of F5.6 at full zoom - third party competitors drop to F6.3. Its size, weight, and (presumably) price are a direct consequence of this.
Like most superzooms, though, it's really not terribly good wide open at telephoto - contrast is low, and it struggles to render much in the way of fine detail at all. Sharpness is OK in the very centre of the frame, but the further you move towards the edge, the worse things get. This is illustrated in the example below, shot at 300mm F5.6, which is pretty typical of our experiences with several copies of the lens. It's just not very sharp at all; there's scarcely any fine detail in the feathers, and a there's a blue 'glow' visible along high contrast edges.
|300mm, 1/640 sec F5.6 ISO 200||100% crop, centre|
|100% crop||100% crop, body|
Of course this has to be taken in context - the 18-300mm may not be performing brilliantly here, but to be fair no other all-in-one lens offers quite the same reach at all. And the image isn't entirely unusable - you just wouldn't want to crop it hard or print it too large. But if you're planning on shooting a lot in this range, you'd surely be better off with a 'proper' telephoto zoom.
Misfocusing at telephoto on D3200
In our real-world shooting using the D3200 as the test camera, the 18-300mm's softness at the telephoto end was compounded by a tendency towards slight misfocusing - taking the edge off whatever pixel-level sharpness was there. This didn't happen in every single shot, by any means, but was disturbingly prevalent nonetheless (and oddly seemed more common for images shot in portrait format).
The examples below illustrate this, with two images shot within a minute of each other from the same position and at the same settings. The first isn't particularly sharp, but is at least properly in focus. The second is slightly out-of-focus, and visibly soft in comparison. Unfortunately here's no way to tell these apart while shooting.
|300mm, ISO 100 F5.6, Nikon D3200|
This sort of focus error won't have any real impact if you mainly make small prints, or downsize your photos for sharing on the web. And, as we've said several tmes already, it's visually amplified here by taking 100% crops from a 24MP image. But it does have the effect of further reducing the critical image quality you can achieve with the lens.
One problem often seen with superzooms, especially on smaller SLR bodies, is that the lens will block the built-in flash at wideangle, resulting in a shadow in the lower center of the image. The 18-300mm's considerable bulk means that it's especially prone to this; on the D3200 we used for testing, it blocked a considerable area of the frame at 18mm, and shadowing only disappeared completely when the lens was set longer than 28mm.
|Nikon D3200, 18mm, 2m focus distance||Nikon D3200, 28mm, 2m focus distance|
Note that what we're showing here is essentially the worst-case scenario - on larger bodies such as the D7000 that lift the flash higher, shadowing is likely to be somewhat reduced.