Tamron SP AF 28-75mm XR Di LD ASPH (IF) is probably one of the longest lens names I have encountered so far. Tamron, which released the lens back in 2006, in general is known for coming up with very long (and not so descriptive) names (obviously, this should not bother anyone as long as the lens performs well). The lens retails at about US$350 (as of October 2007) making is quite affordable as an entry level alternative.
The optical construction of the lens consists of 14 elements in 16 groups with 2 eXtra Refractive (XR) glass elements which help make the lens more compact when compared to similar alternatives, 3 aspherical (ASPH) elements and 3 low dispersion (LD) elements. The lens carries SP (super performance) designation, which in normal language means a professional grade build quality. While the build quality might be considered to be professional grade for Tamron, for the rest of us it's rather average, resembling quality found with most other consumer grade lenses from Canon and other manufacturers. Outer barrel is made of plastic, focusing and zoom rings are rubberized but the zoom ring feels a bit sticky. The inner cams wobble a little bit both when the lens is collapsed as well as when fully extended. The lens is pretty light, weighing 510g (18oz) but is not the most compact one on the market, measuring 73 x 92mm (2.9 x 3.6in), however since the inner cams extend during zooming, the length of the lens almost doubles when fully extended. Tamron added a lock button which prevents the cams from accidentally extending during transportation. The lens offers AF as well as full-time manual focusing which is controlled by an AF/MF switch on the side of the barrel. The minimum focusing distance is 33cm, giving a maximum magnification ration of 1:3.9 at 75mm, the minimum aperture range is f/32 and the filter size is 67mm.
The factory box includes Tamron SP AF 28-75mm f/2.8 XR Di LD ASPH, front and rear lens caps, petal-shaped lens hood, manual and registration card. The lens is designed for full-frame cameras, so if you use it on APS-C type bodies with 1.6x crop factor, the field of view will resemble that of a 45-120mm lens on a full-frame body.
|Lens Composition||14 elements in 16 groups|
|Angular Field||75-32 degrees|
|f-stop Scale||f/2.8-f/32, camera-controlled|
|Lens Hood||Petal-shaped (included)
Tamron 28-75mm f/2.8 showcased pretty solid performance in the field, producing images with excellent overall color representation and contrast. Images were quite sharp in the center throughout the zoom range and all tested apertures, however, border quality was somewhat softer at the wider end of the zoom, especially at f/2.8. The f/5.6-f/8 range seemed to be the sweet spot for this lens, with excellent sharpness across the entire frame and throughout the zoom.
Thanks to its relatively light weight, Tamron 28-75mm f/2.8 was quite easy to handle (keep your hands off the focus ring when using the lens in AF mode - Tamron did not decouple the focus ring from AF so it rotates when camera tries to auto-focus the lens). My biggest complain about the lens is its build quality - the lens just feels too flimsy, with too much plastic and constant wobbling of the front lens element. The noisy and slow AF adds to that feeling of dissatisfaction.
The lens produced noticeable vignetting on a full frame Canon 5D at its widest aperture throughout the zoom range. While vignetting on the wider end of the zoom is understandable, the fact that the lens still produces vignetting at 75mm is somewhat disappointing. Fortunately, once you stop down to f/4, vignetting is pretty much gone. And on APS-C body the lens showed practically no vignetting throughout the zoom range, even at the widest aperture settings. The lens did not show any visible distortion, but fell prone to flare predominantly at the wider side of the zoom range and its widest aperture of f/2.8. Color fringing was basically non-existent throughout the frame.
|Tamron SP AF 28-75mm f/2.8 XR Di LD ASPH image gallery...|
Please note that MTF50 results for APS-C and Full-Frame cameras as well as cameras from different manufacturers are not cross-comparable despite the same normalized [0:1] range used to report results for all types of cameras.
Canon APS-C: Tamron 28-75mm f/2.8 showcased quite impressive results in the lab. Center performance was top notch throughout the zoom range and throughout the tested aperture settings. Here the lens performance rivals that of even most fixed focal lenses. Border quality was pretty solid in most situations as well - with the exception of f/2.8, where the lens is somewhat softer, border performance is outstanding. Overall performance (throughout the zoom range) peaks around f/8. The lens also shows the most balanced results at f/8. The peak performance will get you outstanding 19in and 16in prints in the 28-50mm and 75mm ranges, respectively. Conclusion? This lens delivered one of the biggest surprises when it comes down to resolving power. Who knew that behind a (somewhat) cheesy plastic shell you can find such a good performer?
On an APS-C body, the lens produced low to moderate levels of chromatic aberration. CA is highest towards the wider end of the zoom range and at 28mm if averages ~0.8px in the center and ~1.25px around borders with wide open aperture. Once stopped down to f/4 and beyond, CA in the center is decreased to quite minimal levels, averaging ~0.5px, while CA around borders hovers around ~0.8px (throughout the rest of the aperture range). CA is also is less pronounced towards the longer end of the zoom range, and in the 35-75mm range it averages ~0.6px in the center and ~0.9px around borders with wide open aperture (even less so once stopped down).
Canon FF: The lens continued to show very solid performance on a full frame Canon 5D as well. Center performance is exceptional throughout the supported zoom range and all tested aperture settings! Border quality suffers a little bit, with f/2.8 being (again) the weakest point here. Performance at such wide aperture level is average (but not disastrous) throughout the zoom range. However, in the f/5.6-f/11 range, the lens produces quite solid results around borders throughout the zoom. Conclusion? Well, border quality at f/2.8 degraded somewhat, but results are still quite impressive, especially for an 'entry-level' lens.
On a full frame body, Tamron 28-75mm f/2.8 showed somewhat lower levels of chromatic aberration, with CA averaging ~0.7px in the center across the aperture range and throughout the zoom. CA around borders was a bit higher, especially at f/2.8, where it averaged ~1px throughout the zoom range. Once stopped down to f/4 and beyond, CA drops to pretty much insignificant levels, averaging ~0.7px throughout the zoom.
Here are 100% crops, taken with a full frame Canon 5D, comparing image borders at f/2.8 and f/8
Users have plenty a choice these days when it comes down to standard zoom lenses. Canon alone manufactures at least half a dozen standard zoom lenses for the EF mount and another half a dozen for the cropped EF-S mount. Add lenses from Sigma, Tokina and Tamron, and you will simply be overwhelmed with selection. So, if you're looking for the best lens money can get you, then take a look at Canon EF 24-70mm f/2.8L USM, which offers outstanding image and build quality, but is also priced significantly higher then Tamron's 28-75mm f/2.8 lens. You might also want to consider Canon's other L lens - EF 24-105mm f/4L IS USM, which is slightly slower, but also offers a longer coverage along with an image stabilizer. If you're using an APS-C camera and are willing to spend ~US$1,000, take a look at Canon EF-S 17-55mm f/2.8 IS USM, or if your budget is more modest, check out Tamron SP AF 17-50mm f/2.8 XR Di II LD or Sigma 17-50mm f/2.8-4.5 DC Macro HSM.
Tamron SP AF 28-75mm f/2.8 XR Di LD ASPH (quite a name huh?) is full of surprises. The lens shows very solid performance throughout the zoom range along with low to moderate level of artifacts such as vignetting and CA. Price is another strong attractive point here and at ~US$350, Tamron 28-75mm f/2.8 remains one of the more affordable quality lenses out there. I should be careful when saying 'quality', since the build construction of the lens is rather sub par in my opinion - this and a rather weak AF system seem to be the only negative characteristics of this lens.