Camera Accessories

In its new AF18-250mm f/3.5-6.3 Di II LD Aspherical [IF] Macro lens, Tamron has provided an impressive 13.9x zoom magnification yet only added 0.2 mm in diameter and 0.6 mm in overall length to the dimensions of the AF18-200mm Di-II lens. Designed specifically for DSLR cameras with 'APS-C' sized image sensors, this lens covers the equivalent of 27-375mm on Nikon, Pentax and Sony camera bodies and 28.8-400mm on a Canon DSLR. We tested the lens on the new Nikon D60, which lacks a built-in focus drive motor and, therefore, relies on the AF motor in the lens for all autofocusing.

The optical system in the new lens consists of 16 elements in13 groups with an LD (Low Dispersion) glass element and one AD (Anomalous Dispersion) lens in the first group to minimise on-axis chromatic aberration, particularly at long focal lengths. Two hybrid aspherical lens elements have been used to provide a compact optical design and the third lens group has been optically configured to minimise astigmatism while maintaining high zoom power and optimal image quality.

The optical design is also digitally-orientated with the aim of providing angles of incidence that ensure optimal light levels reach the imager over the entire image field throughout the zoom range. High image quality and resolution, adequate contrast and flatness of image field have been primary goals. Multiple-layer coatings on cemented surfaces of plural elements and ordinary elements ensure ghosting and flare due to reflections that occur when light enters through the front element and reflections caused by the imager itself are reduced to the absolute minimum.

A minimum focusing distance of 45 cm is maintained throughout the entire zoom range, providing a maximum magnification ratio of 1:3.5 at the 250mm end of the zoom range. It's not true macro but it does provide some great close-up pictures. Internal focusing makes it easy to use angle-critical filters with this lens. A metal lens mount is provided and a flower-shaped lens hood is included as a standard accessory.

The lens barrel is solidly designed and very compact for the focal length range this lens covers. A broad zoom ring is located towards the camera mount, while a narrow focus ring is situated near the lens hood mounting. Both rings are quite heavily textured to provide a very secure and comfortable grip. The gold ring that characterises the Tamron brand is located between them.

Engraved on the barrel just behind the zoom ring grip are focal length markings for 18mm, 35mm, 50mm, 70mm, 100mm, 200mm and 250mm positions. These marks line up against a line on the lens barrel (which doubles as a guide when fitting the lens on a camera) when focal lengths are adjusted. Engraved behind the focusing ring are distance indicators in feet and metres for 0.45, 1, 2, 3, 7 and 30 metres plus infinity. No depth of field or infrared indicators are provided.

A slider switch close to the lens mount allows users to switch between auto and manual focusing. A zoom lock prevents unwanted barrel extension when carrying the lens/camera combination facing downwards. Image stabilisation system is not provided in this lens. The lens is supplied with end caps and a flower-shaped lens hood. The hood reverses over the lens when it is not in use and locks into place with a bayonet mounting. 

Handling
In use, the AF18-250mm lens was a comfortable match with the Nikon D60 camera on which it was tested. As with other AF/MF lenses, the focusing ring can only be moved when the AF/MF switch is set to MF. It moved very smoothly and covered the focusing range in roughly one sixth of a turn.

The zoom ring was much stiffer, although it also moved smoothly and showed no tendency to 'creep'. Moving from the 18mm to the 250mm setting involved a quarter of a turn, which was good for the zoom range. The zoom lock and AF/MF sliders, though small, clicked positively into place and it was easy to change settings.

We missed the stabilisation when shooting at longer focal lengths, particularly in low light levels and when shooting close-ups with the 250mm setting. Close focusing capabilities were quite impressive, with the lens focusing to 45 cm from subjects and producing a 1:3.5 magnification ratio with the 250mm setting.

Performance
Considering the range of the zoom, the overall performance of the AF28-300mm F/3.5-6.3 XR Di lens we reviewed was above average - and very even across its focal length range. We obtained the best results in our Imatest tests at between two and five f-stops down from the maximum aperture. Performance tailed off at longer focal lengths, although it remained reasonably good for an extended-range zoom. However, when enlarged to 100% or greater, test shots taken at the 250mm setting were not quite pin-sharp.

At all focal lengths, centre resolution was slightly higher than edge resolution, which is to be expected with a lower-priced lens, although the difference was not as great as in some lenses we've tested. The results from our tests can be seen in the graph below.

Lateral chromatic aberration ranged between low and moderate, depending on the focal length used. Our Imatest results are shown in the graph below, where the red line denotes the border between 'insignificant' and 'low' and the blue line marks the border between 'low' and 'moderate'.

The test lens showed no evidence of flare in blacklit shots, regardless of the focal length setting. This confirmed the effectiveness of the supplied lens hood. Bokeh (out-of-focus blurring) was generally attractive.

Barrel distortion was very obvious at the 18mm focal length but it switched to slight pincushioning at 35mm. This pincushioning remained through the rest of the zoom range without increasing significantly. We believe it would have little impact on normal photography.  

Conclusion
Given its extended focal length range, the Tamron AF18-250mm f/3.5-6.3 Di II LD Aspherical [IF] Macro lens represents excellent value for money. It would be a good choice for photographers who want a DSLR body with just one extended-zoom lens that covers the most commonly-used angles of view. Its relatively light weight, compact size and robust construction make it particularly suitable for travellers.

SAMPLE IMAGES

18mm setting; 1/400 second at f/10.

Taken from the same position as the shot above; 250mm setting, 1/800 second at f/6.3.

18mm setting; 1/60 second at f/5.6.

250mm setting; 1/125 second at f/6.3.

250mm setting; 1/160 second at f/8, showing the bokeh (out-of-focus blur) of the lens.

Backlit shot with the 18mm setting showing no evidence of flare or ghosting.

Backlit shot at 110mm focal length. No flare or ghosting is evident.

250mm setting; 1/640 second at f/11.

An enlarged crop from the shot above showing the slight softening caused by the lens.

250mm setting; 1/400 second at f/6.3.

250mm setting; 1/500 second at f/7.1.

120mm setting; 1/125 second at f/5.6.

Picture angle: 75 degrees 33' to 6 degrees 23' (APS-C size equivalent)
Maximum aperture: f/3.5 to f/6.3
Minimum aperture: f/22
Lens construction: 16 elements in 13 groups
Lens mounts: Canon, Nikon, Pentax, and Sony
Diaphragm Blades: 7
Minimum focus: 0.45m throughout zoom range
Filter size:  62mm
Dimensions (Diameter x L): 74.4 x 84.3 mm
Weight: 430 grams