Focusing, image sharpness and quality
Focusing
The speed of focusing with this Piezo Drive model certainly shows an improvement over the original 18-270mm lens, and there is no audible noise from the motor. It is quicker to lock on at wider focal lengths than towards the 270mm end, but remains reliable throughout. The Piezo Drive isn’t as fast as some USM lenses we have tested, but for such a small lens and at this price the performance is admirable.
The 49cm closest focus is a great feature, and by combining it with the longer focal lengths it means a 1:3.8 magnification can be achieved for close-up shots. The Vibration Compensation is really impressive and the lens appears noticeably steadier through the viewfinder than some more expensive models. The results confirm that using the stabilisation allowed sharp shots a full 4 stops below an otherwise achievable shutter speed.
Image sharpness and quality
There are signs of lens distortion, mainly at the extremes of the focal range, with fairly significant lens barrelling at the widest focal length. This turns to pincushioning from 50mm and becoming significant by the full 270mm extension. Purple and green fringing are also prominent at 18mm in areas of high contrast.
The lens has a definite sweet spot between f/8 to f/11, although performance at wider apertures is not far behind, with only a slight loss in sharpness at f/5.6 and even f/4 when the lens is at its widest focal length. Sharpness falls more significantly with smaller apertures, and settings beyond f/22 are best avoided throughout the focal range. Between 18mm and 200mm the lens maintains similar resolving performance on our chart, but resolution drops more significantly at the 270mm focal length.
Superzoom lenses are often criticised for their lack of sharpness and this was an issue on some early models. However, the technology in these modern lenses has gone a long way to correcting this.
When comparing the results taken on the Canon EOS 7D using both the Tamron 18-270mm and our standard test lens, the Sigma 105mm Macro, readings from our resolution chart test are noticeably softer with the Tamron. This was also seen in real-world comparisons of the results with similar images taken on Canon EF 70-200mm f/2.8L IS and 24-70mm f/2.8 L lenses – although these lenses cost nearly four times the price and weigh almost four times as much.
The use of Vibration Compensation appeared to have no visible effect on sharpness when used handheld at suitable shutter speeds compared with tripod use without stabilisation.
Images: These two images taken from exactly the same spot show the huge range of focal lengths on offer from this lens. Both images are at f/11
