Studio Tests - APS-C format
The Tamron 70-200mm Macro performs well on the APS-C format, benefiting as usual from the 'sweet spot' benefits of low distortion and minimal vignetting. Resolution is also impressive, matching or exceeding the much more expensive Canon 70-200mm F2.8 L IS USM at all settings except wide open at 135mm; and whilst we have to be careful about comparing test results directly across brands, it's clear that it even challenges the superb Nikon AF-S VR 70-200mm F2.8G at the extremes of the zoom range (although not in the middle).
|Resolution||A generally impressive performance, let down only by some softness wide open in the middle of the zoom range (particularly at 135mm). Optimum apertures tend to be around F5.6-F8, with diffraction impacting negatively on sharpness at smaller apertures, and F32 best avoided altogether.|
|Chromatic Aberration||The non-zero values in the central regions of the frame at F2.8 indicate a degree of axial chromatic aberration, however this disappears completely on stopping down to F4. Lateral chromatic aberration is well controlled, with just a little red/cyan fringing visible at the extremes of the zoom range. Overall this is about as expected for this class of lens and is little to worry about.|
|Falloff||We consider falloff to become perceptible when the corner illumination falls to more than 1 stop less than the centre. As usual for a full-frame lens used on APS-C, vignetting is simply a non-issue here.|
|Distortion||Distortion is very low, from 0.71% barrel at 70mm, through neutral at 100mm, to -0.49% pincushion at 200mm. It's very unlikely that this will ever have any negative impact on real-world photos.|
Third party lenses have something of a reputation for less-than-neutral colour balance, so in this new test we measure any colour cast introduced by the lens in comparison to the camera manufacturer's 50mm lens (generally considered a good standard for neutrality).
In this test, the camera is pointed towards an evenly illuminated white wall, and light entering the lens completely diffused using an 'Expodisc' white balance filter. A custom white balance is taken using the 50mm lens (in this case the Canon 50mm F1.4 USM), then exposures made using the 50mm lens and the lens under test (in this specific comparison we've also included the Canon 70-200mm F2.8 L IS USM). The RGB values from the centre of the frame are reported (measured as an 11x11 average).
|Canon 50mm F1.4 USM
(188, 188, 188)
|Canon 70-200mm F2.8 IS
(184, 187, 191)
|Tamron 70-200mm F2.8
(182, 182, 183)
Here we can see that the Tamron has an effectively neutral colour balance when compared to the Canon 50mm F1.4 USM, and indeed that the Canon 70-200mm F2.8 L IS USM introduces a very slight cyan cast (although this is extremely unlikely ever to be a significant issue in real-world use, and if necesssary can be corrected using a custom white balance).
Specific image quality issuesAs always, our studio tests are backed up by taking hundreds of photographs with the lens across a range of subjects, and examining them in detail. This allows us to confirm our studio observations, and identify any other issues which don't show up in the tests.
Softness wide open
About the only obvious issue revealed by our studio tests is softness wide open in the middle of the zoom range, and this does show up to a certain extent in real-world shots. Below are a couple of 100% crops showing the kind of results you can expect to get from out-of-camera JPEGs; as with the Canon 70-200mm F2.8 L IS, detail is still being resolved, just at low contrast, and can be extracted by judicious use of the unsharp mask tool (although at the expense of some increase in image noise).
|93mm F2.8, EOS 40D||100% crop, centre of frame|
|128mm F2.8, EOS 40D||100% crop, centre of frame|