Not long ago a 28-300mm lens was referred to as a superzoom. Now with the advent of smaller sensors, lens manufacturers are producing 18-200mm lenses like the Tamron 18-200mm f3.5-6.3 Di to cover the equivalent zoom range for digital SLR cameras. This is stretching the range of what lens designers can achieve so I think it’s fair to say that all lenses like this offer convenience but at a price in terms of image quality. Optical performance from this lens and superzooms in general is now surprisingly good - considering their zoom range. So if you are interested in family snaps, mostly on holiday and taken in good light then the Tamron 18-200 f3.5-6.3 Di is aimed at you. Tamron themselves call this a “travelzoom”.
If you normally print pictures no bigger than 6x4 inches then results with this lens and a digital SLR camera will be far better than from a digital compact. However if your interest in photography is more serious, then the drawbacks may make a two lens outfit the best option. Image quality with the Tamron 18-200mm f3.5-6.3 Di is OK in the center of the frame at full aperture but quite soft round the edges - adequate only for small prints. Stopping down to f5.6 improves central sharpness a lot, but corners are still slightly soft.
Stopping down to f5.6 improves central sharpness a lot, but corners are still a bit soft. Very noticeable at 18mm is the high level of barrel distortion - any straight lines away from the middle of the frame become curves. Most wide angle zooms have some distortion like this but it’s usually not that obvious - Unfortunately with the Tamron 18-200 f3.5-6.3 XR Di II it is fairly obvious. Over the rest of the zoom range, image quality follows much the same pattern, with fairly good central sharpness but a big drop in performance in the corners. Distortion is only really obvious at the 18 - 24mm end of the zoom range but it is there throughout the range - changing to pincushion distortion at the long end of the range. Another interesting characteristic of the test images is the high contrast on hard edges but low levels of detail in other areas. Some images look as if they have already been digitally sharpened - edges of background figures look sharp but hair and faces are just coloured blobs. All of this is designed to produce ready to go images, good enough for small prints, but less desirable if you want the absolute best quality your digital SLR can produce. That really is the choice here - if you want convenience and don’t plan on having an exhibition of your photos any time soon, this is a well made lens that will help you photograph anything that comes your way, but it’s a compromise. If image quality really matters then my choice would still be two lenses - something like an 18-70 plus an 80-200 - or if you really want just one lens have a look at the newly released Tamron 18-250 f3.5-6.3 Di II LD which has better performance overall and a bigger zoom range. It comes at a higher price, but in my opinion if you’re asking, is it really worth the extra cost over the Tamron 18-200? Then the answer is an emphatic yes.