Review of the Tamron 18-250mm f/3.5-6.3 Di ll Macro

www.intro2020.co.uk Announced last September at Photokina, the Tamron 18-250mm is currently the longest lens in its class, offering a 13.9x zoom for APS-C sensor sized DSLRs. The design concept is based on that of the Tamron 18-200mm f/3.5-6.3 XI Di II LD Macro, with very little added in size and weight. In fact, there’s just 0.2mm added in diameter, 0.6mm added to the maximum length and a 7g increase in weight. That’s impressive, but what else does it have to offer? Specification Designed purely for APS-C sized sensors, the lens offers the 35mm equivalent of 27-375mm on most APS-C cameras, and 28.8-400mm on Canon cameras. On top of this, it offers a minimum focusing distance of 45cm throughout the entire focal range, which, at 250mm, offers a maximum magnification ratio of 1:3.5 (equivalent to 1:2.3 on 35mm). This makes it a capable close-up lens, if not a true macro, but allowing the best of both worlds. Optically, the lens features one LD (Low Dispersion) glass element and one AD (Anomalous Dispersion) glass element, both situated on the first lens grouping to reduce on-axis chromatic aberration at the 250mm end. A pair of hybrid aspherical elements keep the overall lens compact, while the third group has been redesigned from the 18-200mm lens to compensate for distortion and astigmatism, Tamron claims. Tamron has also used internal surface coatings on the cemented surfaces of plural lenses (ie, elements that have been ‘glued’ together within the lens) and have added a new multi-layered coating on single elements. The aim of these applications is to reduce ghosting and flare, caused by stray light bouncing around inside the lens. This is even more crucial on digital SLRs due to the higher reflectivity of sensors compared to the matt emulsion surface of film. Handling The lens is available for Canon, Nikon, Pentax and Sony/Konica Minolta mount cameras. For this review, we used it in combination with a Canon 400D, the current best-selling consumer DSLR. On this camera, the lens felt well balanced, particularly at the compact 18mm focal length. In fact, the lens is little longer than a standard zoom, but the extension to 250mm does (unsurprisingly) add some length. However, compared to the weight of some other lenses, the Tamron is still easy to operate, without increasing stress on your arm, which in turn increases the danger of camera shake. This is mostly due to its all-plastic outer construction, comprising of the outer barrel with two inner barrels, extending as the focal length is increased. It’s still subject to the dangers of camera shake though, especially with Canon and Nikon cameras without anti-shake CCDs. This lens doesn’t have any stabilisation, so it would be interesting to use it with a Pentax or Sony camera with onboard stabilisation, to ascertain the difference. One problem with regards to this, is that the maximum aperture is quite slow, especially the f/6.3 aperture at 250mm. Unless you increase your ISO settings, the chances of hand-holding the lens in average conditions are practically nil. The choices are either to increase ISO (and therefore noise), or to use a tripod. Using a tripod is the best option for best image quality, but carrying 4kg of bulky metal cancels out the advantages of a lightweight lens. For the target customer – those who want an easy, all-in-one, lightweight solution – increasing the ISO is the most practical option. The lens has two focus options – Manual and Auto – and never the twain shall meet. Unlike some lenses, the Tamron 18-250mm only offers manual focusing when the lens is set to manual (forcing the focus in Auto mode will meet with resistance and damage the AF motor). I personally prefer the dual systems, which allow fine focus adjustment, especially when shooting at wide apertures with a narrow depth of field. Image Quality I’m sure that given time and unlimited funds, a lens covering this range could be made that would be fantastic but highly expensive. But a lens to sell to the masses for their budget DSLRs has got to have some give and take. Our main concern is with the small maximum aperture, which inevitably leads to some camera shake at the long end, due to the necessity of having to use longer shutter speeds. In other ways though, the lens performed remarkably well. Throughout the range, centre sharpness is very good but especially at the wide 18-50mm range. Edge sharpness compromises this somewhat but by stopping down the lens to around the f/8 mark, performance matches that of more expensive lenses. At the telephoto end, resolution is lower, which we'd expect, but is still well within acceptable bounds. Fringing Problems The edges also pose fringing problems, with a two to three-pixel rise of chromatic aberration from wide to tele. In the centre, this rate remains constantly under 0.5 pixels, which is a good performance. Again, reducing the size of the aperture minimises this, with f/8 once again producing the best average performance. A lens of this type is also bound to be a victim of distortion, and at 18mm this is certainly the case, with quite severe barrel distortion, though by 24-28mm it is negligible. From there onwards, the lens displays gradually worsening pin-cushion distortion. Up until 100mm this is very slight and even at 250mm it is still relatively minor and less than expected. Verdict While the lens’s performance may not match that of those with a shorter zoom range, the fact remains that to a large number of people this is going to be a tempting lens. When you judge it in terms of value for money, performance is actually very good. It matches and even exceeds the performance of similar and more expensive lenses – in some areas. We would still rather have two or three lenses covering this range for optimal performance, especially faster lenses for medium to low light. Of course, that would incur more cost and weight, though perhaps less weight than a half-decent tripod. The need to stop the aperture down for decent performance is also a limiting factor – and, while this is true of most lenses, it is even more true of this model. The Tamron engineers have fulfilled their brief, however, and must be commended for pushing the boundaries of budget optics a little further. The 18-250mm is a useful and cost-effective, if slightly flawed, all-round optic, especially if you have a stabilised CCD-based DSLR. What Digital Camera Score 83%