The Tamron 18-270mm F3.5-6.3 Di II VC PZD performs reasonably well for a superzoom, although it's highly variable across the zoom range. It gives impressively sharp images at wideangle, but gets progressively softer at longer focal lengths, and is distinctly weak wide open at 270mm. But stopped down to F8 or F11, it's just fine.
|Sharpness||At 18mm sharpness is impressive right across the frame even wide open, and improves only marginally on stopping down, with best results around F5.6. The lens gets progressively softer on zooming in, however, with the corners of the frame suffering more than the centre. At longer focal lengths it's generally best shot at F8 or even F11 whenever possible. The lens lets you stop down to very small apertures, especially at the long end, but these are generally best avoided as sharpness is poor due to diffraction.|
|Chromatic Aberration||Chromatic aberration is most pronounced at the two ends of the zoom - there's barely any in the middle of the range (around 100mm). At both 18mm and 270mm it gives visually-objectionable green/magenta fringing. Note that Nikon SLRs will compensate for this in their JPEG processing, but other brands won't.|
|Vignetting||Vignetting is generally very low - at worst there's slightly over a stop wide open at 18mm, which pretty well disappears on stopping down the F5.6. Overall this nothing to worry about in practical use.|
|Distortion||Like all SLR superzooms the 18-270mm suffers from pretty pronounced distortion. At wideangle there's quite strong barrel distortion (3.2%), with recorrection towards the corners. This turns to pincushion across the rest of the range, which is worst around 50mm (a rather severe -3.3%).|
The 18-270mm's macro coverage is very similar to its predecessor's, which is to say perfectly respectable, although it's now soundly beaten by Sigma's latest 18-250mm f/3.5-6.3 DC Macro OS HSM. Our measured closest focus distance (at full telephoto, in manual focus) is 43cm, slightly shorter than Tamron's specified 0.49m. Note that you won't be able to autofocus quite so close.
Image quality here is acceptable, but not great. The image is very soft overall at F6.3, with low contrast and blurring that's a signature of spherical aberration. But the centre sharpens up dramatically on stopping down to F8, beyond which it gradually degrades again due to diffraction. With our flat test chart the corners are very soft wide open, and while they improve on stopping down, they never really sharpen up fully. This most likely reflects curvature of field.
Full Frame Coverage
The Canon, Nikon and Sony mount versions of this lens will mount on full-frame DSLRs; on Nikon cameras DX crop mode will be automatically selected (and the camera will therefore shoot at reduced resolution). On Sony cameras you can select the APS-C crop manually. However the lens's image circle doesn't cover the 35mm full frame format at any focal length, giving severe vignetting regardless of focus distance. The examples below were shot with the lens set to infinity focus.
The bottom line is that if you shoot using a full frame camera - or plan to do so in the near future - a lens with appropriate coverage really does make far more sense (and for a superzoom, that means something like a 28-300mm).
The 18-270mm features Tamron's own 'Vibration Compensation' system, designed to allow hand-holding at slower shutter speeds than usual without seeing the blurring effects of camera shake. It's been completely redesigned from the previous model, and unusually, Tamron makes no specific claims about its effectiveness. The mechanism is effectively silent when operational, with only the impressive stabilization of the viewfinder image betraying the fact that it's running.
To determine the effectiveness of the VC system we subjected the 18-270mm to our studio image stabilization test, using the wideangle and telephoto settings plus one mid-range focal length (50mm). The subject distance for these tests was approximately 2.5m for 18mm and 50mm focal lengths, and 4m for 270mm; the test camera was the Canon EOS 650D.
We take 10 shots at each shutter speed and visually rate them for sharpness. Shots considered 'sharp' have no visible blur at the pixel level, and are therefore suitable for viewing or printing at the largest sizes, whereas files with 'mild blur' are only slightly soft, and perfectly usable for all but the most critical applications.
|18mm VC OFF||50mm VC OFF||270mm VC OFF|
|18mm VC ON||50mm VC ON||270mm VC ON|
The 18-270mm PZD fares reasonably - if not brilliantly - in our stabilization tests. Surprisingly, though, it lags slightly behind both its predecessor and the Sigma 18-250mm f/3.5-6.3 DC OS HSM, and some way behind the best in class (the Canon EF-S 18-200mm f/3.5-5.6 IS, according to our tests). The main point compared to the Sigma is that once the shutter speeds drop to about 2 stops slower than the 'safe' speed, the VC system tends to give images which aren't perfectly sharp, but just slightly blurred instead.
How much difference this makes in practice, of course, depends on how you view and present your images. If you mainly show your images as downsized versions on internet photo-sharing sites, or make small prints, the difference will be essentially academic. And, of course, this is a lot better than having no stabilization at all.
Real world examples
The examples below should give you an idea of how well Tamron's VC system behaves in everyday shooting. In both cases we've used shutter speeds at least two stops slower than we'd be able to reliably handhold ordinarily, so the image would be hopelessly blurred without stabilization. Instead we've taken advantage of the ability to shoot at slower shutter speeds to stop down a bit and keep ISOs relatively low, for better overall image quality.
59mm, Canon EOS 650D
270mm, Canon EOS 650D
|1/25 sec, F6.3, ISO 400||1/125 sec, F8, ISO 100|
|100% crop, upper right||100% crop, centre|