Design

Tamron appears to have a philosophy of making its designs functional rather than pretty, and the 18-270mm is correspondingly unlikely to win any awards for its build and styling. The feel of the materials and the overall fit and finish isn't quite as refined as its rivals, but having said that the underlying build quality is broadly similar. The mount is metal, and the barrel is constructed of lightweight plastics with a metal sub-structure. The barrel is dominated by the broad zoom ring, with the focus ring towards the front.

Two switches on the side control the autofocus and vibration correction mechanisms; these are noticeably larger and easier to operate than their counterparts on the Canon and Nikon 18-200mm lenses. There's also a switch to lock the zoom at 18mm, conventionally-placed on the top of the lens barrel. This is worthwhile on such a lens with its heavy front elements, which can cause the lens to extend under its own weight when the camera is carried over the shoulder.

On the camera

The lens feels ideally balanced on larger DSLRs such as the D300, but can feel a little front-heavy on smaller bodies such as the D40/D60 range (although still perfectly usable). Controls are well-placed; the zoom ring falls naturally to hand, and the manual focus ring is readily operable by the forefinger when required. The AF and VC switches are also well-placed within easy reach on the side of the lens barrel, and the zoom lock perfectly accessible. Overall, that decidedly utilitarian design approach pays dividends in terms of ease-of-use.

One note of caution though; on smaller SLR bodies such as the D60, the lens will block the built-in flash at focal lengths wider than 24mm, resulting in a shadow in the lower center of the image.

Autofocus

The 18-270mm VC uses a small micro-motor for autofocus, and this is the weakest point of the design. It feels rather sluggish when compared to either Nikon or Canon's 18-200mm lenses, although to be fair the motor is at least reasonably quiet (although not silent like the Nikon's AF-S motor). On the bodies used for testing (Nikon D300 and D90) AF performance was relatively slow and sometimes extremely indecisive, especially at telephoto, presumably hindered by that slow maximum aperture (most autofocus systems are only specified to work reliably with lenses that are F5.6 or brighter).

On the D90, the lens was also occasionally unable to confirm focus with subjects which we'd normally not expect to be a problem, instead dithering for a few seconds before giving up and sometimes giving a clearly misfocused image. However this wasn't a particularly frequent problem; also it was normally easy enough to spot in the viewfinder when the lens was struggling, and either switch to manual focus or take a couple of 'safety shots'. As always, it must be noted that focus speed and accuracy is dependent upon a number of variables, including the camera body used, subject contrast, and light levels.

Zoom creep

Zoom creep is the tendency for a lens to extend or under its own weight when pointed downwards (or collapse when pointed upwards), and is a fairly common characteristic of superzooms. It can be a problem when carrying the camera over your shoulder with the lens hanging downwards, as having the zoom continually extend to its maximum length is not just irritating, but also makes the lens more vulnerable to being knocked and damaged.

The 18-270mm suffers from zoom creep more than most, and if you habitually carry the camera with the lens pointing downwards you'll find it setting itself to 270mm on a regular basis. With our test sample this happened pretty well any time the lens was set to a focal longer of 35mm or longer; conversely at 200mm or shorter and with the camera pointed upwards, the lens tended to collapse towards 18mm. Now if you're prepared to reset the lens to 18mm between shots then the problem essentially goes away (ironically the lens tends not to creep at all at this focal length, making the zoom lock switch near-redundant). Also if you prefer to carry the camera in your hand with the lens horizontal rather than vertical, creep effectively becomes a non-issue too.

However zoom creep can also be a problem when pointing the camera either upwards or downwards when shooting, as it means that the lens can attempt to zoom under its own weight; this isn't much of a problem when shooting hand-held (simply keep hold of the zoom ring), but can become a genuine problem when shooting at slow shutter speeds with the camera on a tripod, at which point holding the zoom ring is not an option. To be fair this is not a typical scenario with this lens (the whole point of a stabilized superzoom is to travel light, which likely means leaving the tripod behind), but it could be a concern to some users.

Dependence of apparent focal length on focus distance

This lens's angle of view widens dramatically on focusing from infinity to 0.45m, especially at the telephoto end. This is a common trait with superzooms (the Canon and Nikon 18-200s behave in just the same way), but it does mean that at a focus distance of 2m, that 270mm telephoto ends up looking more like 180mm. In context, it is worth bearing in mind that long telephotos generally tend to used more for distant subjects, in which case the lens naturally behaves as a 'true' 270mm.

Lens body elements

	The lens comes in versions for Canon and Nikon DSLRs. Our sample was the Nikon F model, and featured an unusual, slightly bronzed mount.
	The filter thread is 72mm. It does not rotate on autofocusing, which should please filter users.
	The AB003 bayonet-mount hood is provided as standard, and fits positively onto the front of the lens. It's reasonably solidly made (if slightly flexible), and features ribbed mouldings on the inside to minimize reflections of stray light into the lens. White dots on the outside of the hood aid alignment for mounting, and it reverses neatly for storage.
	The zoom ring has a 34mm wide ribbed rubber grip, and rotates a mere 80 degrees clockwise from wide to telephoto (the 'right' way for Nikon owners, but opposite to Canon lenses). The action is distinctly uneven, with a pronounced increase in stiffness around 70mm when zooming from wide to tele (although not in the opposite direction). The front element extends fully 89mm on zooming, with a little lateral play at 270mm.
	The 11mm wide focus ring rotates just 60 degrees anticlockwise from infinity to 0.5m, again matching Nikon lenses and opposite to Canons. A basic distance scale is marked in feet and meters. The focus ring travels slightly past the infinity position, and rotates during autofocus. The feel of the focus ring is smooth but rather loose; coupled with the short travel, this makes the lens far from well suited to precise manual focus.
	Two large, well-placed switches on the side of the lens barrel control the focus and VR systems. The top one switches focusing between auto and manual modes; and the lower one turns vibration correction on and off. Both are easily reached with the right thumb.
	Tamron have included a switch which locks the zoom at the wideangle position to prevent 'zoom creep'. It's a fairly basic design, which simply slides into a slot in the lens barrel to lock.

Reported aperture vs focal length

Here we show the maximum and minimum apertures reported by the camera at the marked focal lengths.

Focal length	18mm	35mm	50mm	70mm	100mm	200mm	270mm
Max aperture	F3.5	F4.2	F4.5	F5.3	F5.6	F6.3	F6.3
Min aperture	F22	F29	F29	F36	F36	F40	F40

The 18-270mm is about a third of a stop darker than the Canon and Nikon 18-200mm lenses from around 100mm onwards - not a significant difference in real world use.