The Tamron 18-250mm f3.5-6.3 Di II LD Aspherical [IF] Macro, to give it’s full name, was Tamron’s star of the show at the 2006 Photokina in Germany. Judging by the amount of advertising around - they even had pictures of it under your feet on the stairs - Tamron obviously thought it was something special.
Most superzooms for digital SLR’s stop at 200mm, so extending the range to 250mm gives you a film equivalent of roughly 28-400 which would have existed only in photographers dreams not that long ago. All this is made possible by computer design and new manufacturing techniques using moulded aspherical components to produce corrections that solve optical problems at a cost people other than NASA can afford. The Tamron 18-250 uses all the latest techniques - Including LD - Low Dispersion glass, Aspherical elements and AD - Anomalous Dispersion glass, so I think it’s fair to say that the Tamron 18-250 represents the state of the art in this type of lens. Build quality is excellent, although that’s to consumer rather than professional standards. Tamron don’t include this lens in their XR - compact - series, but it weighs only 430g, so could easily be carried around all day without any hardship.
Image quality in superzooms is usually adequate to good, and follows the pattern observed with the Tamron 18-200mm XR and Sigma 18-125 DC, with a reasonable level of performance, but none of the bite or real high levels of detail that any DSLR can provide with a fixed focal length lens, or pro quality zoom. With most superzooms, even if you stop right down to f11 or better, real sharpness will only be found in the center of the frame. All lens designs involve compromise, and when you buy a zoom lens with a very wide range you usually have to expect a lower level of performance. The formula in very general terms, for lenses at the same price level, is - Wider zoom range equals poorer optical quality. What you’re buying with superzooms is convenience, and normally you just have to accept that this means a lower level of optical performance.
Of course it would be nice if that wasn’t the case, so any manufacturer who can produce a lens with a wide zoom range at a reasonable price that does perform well throughout the range would have something to shout about. Tamron are doing just that about their new Tamron 18-250 Di and judged by the results of this short test - They’re right. The Tamron 18-250 is different in several ways. Firstly the range - 18-250mm when nearly every other competitor - including Tamron’s own - are 18-200mm. That means a film equivalent of just under 400mm rather than 300mm at the long end, which is reaching the limit of what is usable hand held. As it’s unlikely that this lens will spend much of it’s life mounted on a big heavy tripod, the odd seeming choice of focal length actually makes perfect sense. The Tamron 18-250mm is also somewhat more expensive than most 18-200mm competitors, so are you just paying for that extra 50mm or is there more to it?
Test results very quickly showed that you’re getting a lot more than a few extra mm’s for your money. Full aperture performance is good in the center and falls off in the corners just like any other superzoom, but stop down even just to f5.6 and results are very, very good - I’m surprised at how good. Farther along the zoom range from about 50-100mm even full aperture performance over most of the field is very good. One noticeable characteristic is that the drop in sharpness away from the center of the field, when it comes, is more dramatic than usual, but, as it’s right into the corners before it happens, chances are you’ll never notice. From about 100-250mm sharpness gradually drops, but not drastically - even at 250mm it’s still pretty good. I hadn’t really been looking forward to reviewing this lens - Having tried various superzooms in the past, the conclusion is usually along the lines of - not bad considering the zoom range - followed by lots of “It would be unrealistic to expect this sort of lens to perform along the lines of professional optics etc” - but this lens is a surprise - It still has high levels of distortion at the wide end, and if you look at images at 100% there is some CA - BUT, and it’s big BUT - this is a really good lens. Used carefully the Tamron 18-250 is very sharp. Tamron are quite right to shout about it. So, if you’re in the market for what Tamron call a “travelzoom” for your digital SLR camera, this is the best I’ve come across, and there is no question to me that it’s worth the extra cost over competing 18-200’s.
Nikon Note: Tamron now produce a Nikon version with a built-in AF motor, but check that you buy the correct version - older versions of the lens won’t autofocus with some new Nikon DSLRs like the Nikon D3000 and Nikon D5000.