Tamron 18-270mm f/3.5-6.3 Di II VC LD Aspherical IF Macro AF

(From Tamron lens literature) Tamron Co., Ltd., has announced the development of a unique ultra high power zoom lens-the Tamron AF18-270mm ƒ/3.5-6.3 Di II VC LD Aspherical (IF) MACRO (Model B003), the first digital SLR lens in the world that delivers a remarkable zoom ratio of 15X (28-419mm equivalent) and is equipped with a highly effective Vibration Compensation (VC) mechanism.

SLRgear Review
January 5, 2009
by Andrew Alexander

The Tamron 18-270mm ƒ/3.5-6.3 currently holds the title as the vacation zoom with the greatest wide-angle to telephoto zoom range, besting Tamron's own previous effort of 18-250mm by 20mm. It's also the second Tamron lens to employ their VC (Vibration Control) technology, to aid the shooter in controlling camera shake.

The 18-270mm is a Di-II lens, meaning it was designed for the reduced size of a subframe (APS-C) digital sensor. As our lab technician Rob notes, ''you can fit it on a full-frame sensor, but it vignettes like crazy.''

On a Canon digital body this will equate to an equivalent 35mm field of view of 29-432mm, and on a Nikon digital body this equates to 27-405mm. This lens isn't a "constant" lens, in that as you increase the focal length, both the maximum and minimum aperture sizes decrease. The following table reflects the changes as you zoom:

The lens ships with a petal-shaped lens hood, and is available now for around $600.

Sharpness
The Tamron 18-270mm offers a wide range of results, depending on the aperture and focal length. Its best performance for sharpness is only found with the lens significantly stopped down, to at least ƒ/8, making it useful only in scenarios with significant lighting. To its credit, the vibration control gives the lens a bit more of an opportunity to be used in ''lower'' light situations, but even then you'll either be pushing the ISO or seeking a lower aperture where the lens offers marginal results. Let's take a closer look.

Used with the aperture wide open, the lens offers fair to good results for sharpness in the central region, marred only by significant corner softness through every focal length. Any visible central sharpness is degraded when the lens is extended to 200mm or higher (just under 3 blur units in the center, and between 4-6 blur units in the corners at 270mm).

As indicated previously, stopping down the lens significantly helps achieve sharper results. Setting the aperture to ƒ/5.6 dramatically improves sharpness up to 100mm, after that you need to set it to ƒ/8. In fact setting the lens to ƒ/8 gives its best overall performance, the optimal setting being 50mm and ƒ/8, where the lens is almost tack-sharp across the frame.

Above 200mm the lens isn't exceptional - you get the feeling that they found a way to extend an 18-200mm lens to 270mm with a few modifications that, in the end, don't really perform. At ƒ/8 or ƒ/11 image sharpness hovers around the 3-4 blur unit mark across the frame, which isn't bad, but isn't that great, either.

When fully stopped down, the lens offers above-average results at ƒ/22 (around 3-4 blur units, depending on the focal length); any aperture setting smaller than this will produce dramatically soft and uneven results. Apertures in this range are best avoided.

In summary, this lens is the perfect example of the compromises that must be made in the vacation zoom category. It does extremely well in its mid-ranges (50mm, stopped down to ƒ/8) but in almost any other situation it shows some form of softness.

Chromatic Aberration
Tamron handles chromatic aberration fairly well with this lens, especially on the wide end and in the mid-range. At 18mm, CA is a factor, but not especially overt, at 6/100ths of a percent of frame height in the corners and 3/100ths of a percent across the frame; this occurs regardless of the aperture setting.

Between 35-200mm, CA is well controlled. It's only at 200mm and above that significant CA can be found in the corners. Readers may wish to consult our sample photos for a more visual explanation.

Shading (''Vignetting'')
Between 35-70mm, corner shading isn't a factor with this lens. It's only in the wide angle (18mm) and at 100mm and above that light falloff presents a slight issue. At 18mm, there's always at least 1/4EV of corner shading, and if you use it wide open at ƒ/3.5, that increases to 1/2EV. At 100mm, 200mm and 270mm, you get 1/3EV if you use the lens wide open.

Distortion
Predictably, the complex array of lens elements that allows such a vast range of focal lengths in one lens leads to some dramatic results for distortion. When used in the wide angle configuration, the lens provides uniform barrel (''bloat'') distortion up to around 25mm, with dramatic distortion in the corners (1.25%, quite significant). After 25mm, distortion across the frame remains consistently barrel-distorted, but at a moderately low level (around 0.2%, on average) and the extreme corner distortion turns into the pincushion (''squeeze'') style. The worst pincushion distortion at 50mm, where the corners show -0.6% pincushion distortion. Post-processing would be required to correct for these effects.

Autofocus Operation
Autofocus is conducted electrically, without the use of a mechanical screw. Autofocus speed is fairly quick, producing a slight noise during focusing, but nothing objectionable. Focus speed is not as quick as that seen on Canon's USM or Nikon's AF-S technologies, and isn't as quiet, either. The lens will autofocus on the ''screw-less'' Nikon D40, D40x and D60 bodies.

Macro
The Tamron 18-270mm ƒ/3.5-6.3 offers respectable macro capability, with a maximum magnification ratio of 1:3.5 (0.29x) and a minimum close-focusing distance of just over 19 inches (49 cm).

Build Quality and Handling
Tamron has economized on the design of this lens by using a plastic chassis, reducing weight and price, with a textured black finish. However, the lens mount is reassuringly metal and despite the plastic construction there is no noticeable rattling or flexing. The focus ring is mounted near the front of the lens, and the large zoom ring is found closer to the lens mount. Both rings use a nice rubber ridged pattern that is well dampened and easy to grip.

The lens is fairly uncomplicated to use, with only two controls to speak of: one switch to enable or disable the lens' autofocus operation, and another switch to activate or deactivate the vibration control feature. A distance scale is indicated on the lens, in feet and meters; no depth-of-field scale is present.

The zoom function of the lens is controlled by the larger of the two rings on the lens, rotating approximately 45 degrees to extend the lens through its entire range of focal lengths. The ring is made of a tough rubber, with recessed ridges, and is a comfortable 1 3/8 inches wide. The zoom ring is slightly stiff, unsurprising as there are a fair number of lens elements to push out. Zooming out to 270mm adds 3 1/4 inches to the lens' total length, going from a compacted length of 3 3/4 inches to almost double that, of 7 inches. There is some slight flexing of the lens when the lens is extended to 270mm. Zoom creep is a factor with this lens: the weight of the front of the lens will easily pull the lens into its 270mm configuration if held downwards, and slide it to 18mm if held upwards. Tamron has included a zoom lock switch to lock the lens at 18mm to contend with this issue.

The focus ring of the lens, located near the front of the lens, is 7/16 of an inch wide, composed of a deeply ridged rubber. There isn't a lot of travel for the purposes of manual focusing - approximately 30 degrees. There are hard stops at either end of the focusing spectrum, and the lens will focus past infinity. The front element does not rotate during focus operations, making life a little easier for filter users. The lens uses 72mm filters.

Vibration control is fairly good for this lens, and one day in the near future we will be publishing our detailed stabilization tests for this lens; at the moment though all we can say subjectively is that the VC system works well, and is a definite asset for this lens.

The included petal-shaped lens hood reverses onto the lens for storage. The hood is ribbed on the interior, and when mounted, adds almost 2 inches to the overall length of the lens.

Alternatives

If you want the absolute largest range of focal lengths, then at the time of writing (January 2009) this is the lens to get. If you don't need to go past 200mm, here are some other lenses to consider:

Canon EF-S 18-200mm ƒ/3.5-5.6 IS ~$600
Results for sharpness are similar between the two lenses, with a slight edge going to Canon at the telephoto range, however, the Canon tops out at 200mm compared to the Tamron's 270mm. The Tamron is just slightly more capable at contending with chromatic aberration, but shows its flaws at focal lengths the Canon does not extend to (200-270mm). Distortion is similar between the two lenses, and the Canon produces slightly more corner shading. Both feature image stabilization and 72mm filter mounts.

Nikon 18-200mm ƒ/3.5-5.6G IF-ED AF-S DX VR ~$600
The Tamron is noticeably sharper than the Nikon in the majority of focal length / aperture combinations, except at the telephoto end (200mm) where both lenses produce similarly average results. Chromatic aberration is similar between the two, perhaps better controlled in the Tamron in the mid-range (35-70mm). Distortion is similar between the two, and the Nikon shows more obvious corner shading when used with large apertures. Both feature image stabilization and 72mm filter mounts.

Sigma 18-200mm ƒ/3.5-6.3 DC OS HSM ~$380
The Tamron is much sharper than the Sigma, contends better with chromatic aberration, shows less corner shading but produces the same amount of distortion. Both lenses feature image stabilization and a 72mm filter mount.

Conclusion
As the Tamron 18-270mm and the ''name-brand'' competition are all floating around the same price point, the decision of whether to buy this lens or a Nikon / Canon equivalent comes down to how badly you need the extra 70mm of distance. Image quality is fairly consistent between these lenses, with perhaps a nod towards the Tamron, but autofocus speed and quality is better with the competition. For what it's trying to be though, the Tamron produces good results, an excellent alternative to carting around several lenses.

Sample Photos

The VFA target should give you a good idea of sharpness in the center and corners, as well as some idea of the extent of barrel or pincushion distortion and chromatic aberration, while the Still Life subject may help in judging contrast and color. We shoot both images using the default JPEG settings and manual white balance of our test bodies, so the images should be quite consistent from lens to lens.

Still Life shot

VFA target

As appropriate, we shoot these with both full-frame and sub-frame bodies, at a range of focal lengths, and at both maximum aperture and ƒ/8. For the ''VFA'' target (the viewfinder accuracy target from Imaging Resource), we also provide sample crops from the center and upper-left corner of each shot, so you can quickly get a sense of relative sharpness, without having to download and inspect the full-res images. To avoid space limitations with the layout of our review pages, indexes to the test shots launch in separate windows.