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by Bob Atkins; created March 2007
If you want one lens to "do it all", with a 13.9x zoom range, the Tamron 18-250/3.5-6.3 beats the 28-300mm (10.7x) and 18-200mm (11.1x) competitors by a significant margin. When used on an APS-C DSLR, such as a Canon Digital Rebel XTi (Black) (review), the Tamron 18-250/3.5-6.3 is equivalent to a 29-400mm lens on a full frame camera.
Despite the wide zoom range, the Tamron 18-250/3.5-6.3 is quite a small lens, measuring only 2.9" in diameter and 3.3" long and weighing 15.2 oz. It's a DiII series lens, which means that the image circle covers only the area of APS-C sized sensors and thus is incompatible with 35mm film cameras and full frame DSLRs.
To improve image quality the Tamron 18-250 uses two hybrid aspherical elements, one AD (anomalous dispersion) element and two LD (low dispersion) elements. The $499 price of the lens includes a hood and a six year warranty. It is available in the following versions:
When is it most valuable to have a wide-range zoom and not be forced to carry or change lenses? Travel and dusty environments are the most common situations. If you don't change lenses, you're much less likely to get dust on the digital sensor.
The 18-250mm focal length range sounds useful for everything from landscape work to portraits, sports, and wildlife photography. Unfortunately, the relatively slow aperture in the portrait range (f4.5 at 50mm, f5.0 at 70mm) means that a distracting background will be rendered in sharper focus than with a faster prime lens such as the Canon EF 50mm f/1.8, $80 (review). For sports photography, the slow aperture means that you won't be able to use the fast shutter speeds required to freeze action, unless you set the camera to ISO 800 or higher, which reduces image quality. For wildlife, the slow aperture means that you'll need a tripod, especially given the lack of image stabilizer in the lens.
At the telephoto end of the range, in particular, the slow maximum aperture and the lack of image stabilization makes this a lens that will perform best outdoors in bright light.
I used this lens for several days and compared the results with those from two shorter range zooms in the same price class, the Canon EF-S 17-85mm f/4-5.6 IS USM, $414 and the Canon EF 70-300mm f/4-5.6 IS USM, $549 (review).
The maximum aperture is f3.5 at 18mm, dropping to f4.0 at 35mm, f4.5 at 50mm, f5.0 at 70mm, f5.6 at 100mm and f6.3 above 200mm.
The quality of the images from the Tamron lens were similar to those from the Canon 17-85. At the widest setting, barrel distortion and vignetting are noticeable. Both lenses were sharp in the center, with softening at the edges. Edge quality improved with both lenses by closing down the aperture one or two stops. Distortion from the Tamron 18-250 was very low by 28mm. Vignetting, or darkening of the images at the corners, was reduced significant by closing down the aperture by one or two stops.
In the 100-250mm telephoto range center sharpness of the Tamron lens was good, even wide open, though "wide open" is only f6.3 from 200-250mm. Image quality dropped off at the edges of the frame due to lower sharpness and chromatic aberration. Stopping down to f8 improved edge sharpness slightly. In comparison, images from the Canon EF 70-300mm f/4-5.6 IS USM were sharp in the center and at the edges. The Tamron 18-250 exhibited mild pincushion distortion at focal lengths from 100mm to 250mm. Vignetting was eliminated by stopping down to f8 at 100mm and by stopping down to f11 at 250mm.
Handholding a lens at 250mm with an APS-C DSLR requires a shutter speed of 1/400s or shorter to freeze camera shake. With a maximum aperture of f6.3, that means bright light or a high ISO setting will be required. When used with a body with internal image stabilization, such as the Sony A100 or Pentax K10D, it will be easier to use at longer focal lengths, but keep in mind that in-body image stabilization is less effective at longer focal lengths.
Note that distortion and vignetting can be corrected with digital post-processing.
The Tamron 18-250 focuses down to 0.45m at all focal lengths and gives a maximum magnification of 0.28x. There is a significant change in focal length as the lens is close-focused at the 250mm setting. Despite the fact that the ring on the lens is set to 250mm, the actual focal length is about 125mm, a common side effect when using internal focus lenses. The consequence of this is that you get less magnification that you would otherwise expect when using the Tamron lens at close range compared with using the Canon EF 70-300/4-5.6IS at the same distance and focal length.
One alternative to the Tamron 18-250 would be a two-lens set: the first covering the wide to normal end of the range and the second the normal to telephoto end. In the Canon EOS system, the Canon EF-S 17-85mm f/4-5.6 IS USM, $414 and Canon EF 70-300mm f/4-5.6 IS USM, $549 (review) are obvious candidates. Both have built-in image stabilization and fast, silent, USM motors, at a combined price of double that of the Tamron zoom and a combined weight of 39 oz. vs. the 15.2 oz. of the Tamron. Those serious about image quality would opt for the Canon EF-S 17-55 f/2.8 IS USM, $1053 (review) and the Canon EF 70-200mm f/4L USM, $540 (review). At a combined price of over $2200 and a combined weight of 3 lbs., these will remind you why all-in-one lenses like the Tamron are so popular.
If you want just one lens with an extreme range of focal lengths, the Tamron 18-250 is one of the most capable options. Center sharpness is quite good, but you will have to accept low edge sharpness at telephoto settings. If you value convenience over image quality, the Tamron 18-250 could be a good choice.
Amazon.com sells Tamron 18-250/3.5-6.3 in a variety of lens mounts:
Text and pictures ©Copyright 2007 Bob Atkins
