Tamron SP AF 70-200mm F2.8 Di LD (IF) Macro review
Studio Tests - 35mm full frame
The Tamron maintains its excellent performance on full frame; it benefits from the usual advantage of higher perceived sharpness on the larger format, and chromatic aberration, falloff and distortion are all within acceptable limits. It's at least a match for the Canon 70-200mm F2.8 L IS USM in terms of sharpness across the range, and indeed is noticeably sharper wide open at 70mm.
|Sharpness||Sharpness is overall extremely high, even wide open. The optimum apertures are generally around F5.6-8, but with generally excellent performance from F4 to F16 this lens has an exceptionally broad 'sweet spot'. F22 is also highly usable, but F32 should probably be reserved for emergency use only.|
|Chromatic Aberration||Residual axial chromatic aberration is again clearly visible at F2.8 on full-frame, although its effect is reduced on the larger sensor. Lateral chromatic aberration is kept well under control, with just a little fringing at the extremes of the zoom range. Overall a very good showing from the Tamron.|
|Falloff||We consider falloff to become perceptible when the corner illumination falls to more than 1 stop less than the centre. Falloff is about what we expect from this class of lens, about 1.7 stops wide open, falling to around one stop at F4 and essentially negligible below F5.6.|
|Distortion||Distortion on full frame is a little high, ranging from 1.6% barrel at 70mm to -1.3% pincushion at 200mm, with the neutral point at 100mm. However this is unlikely to be a problem for typical uses of this lens.|
Full-frame compared to APS-C
Eagle-eyed viewers will no doubt have noticed that the MTF50 sharpness data at any particular focal length/aperture combination is distinctly higher on full-frame when compared to APS-C. This may at first sight appear unexpected, but in fact is an inevitable consequence of our presentation of the sharpness data in terms of line pairs per picture height (and thus independent of format size).
Quite simply, at any given focal length and aperture, the lens will have a fixed MTF50 profile when expressed in terms of line pairs per millimeter. In order to convert to lp/ph, we have to multiply by the sensor height (in mm); as the full-frame sensor is 1.6x larger, MTF50 should therefore be 1.6x higher.
In practice this is an oversimplification; our tests measure system MTF rather than purely lens MTF, and at higher frequencies the camera's anti-aliasing filter will have a significant effect in attenuating the measured MTF50. In addition, our testing procedure involves shooting a chart of fixed size, which therefore requires a closer shooting distance on full frame, and this will also have some influence on the MTF50 data.
Specific image quality issues
As 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. Our test sample of the lens was in Canon EF mount, and we tested it on a range of bodies from the low-end EOS 450D to the professional EOS-1D Mark III.
The complex optical design of 70-200mm F2.8 lenses generally makes them rather susceptible to flare under unfavorable circumstances, and the Tamron is no exception. It's still capable of handling most everyday situations perfectly well, but can occasionally run into serious problems, especially with strong light sources just outside of the frame.
Our two 'real-world' flare examples show this clearly; with the sun placed in the corner of the frame at 70mm, the flare pattern is generally less intrusive and problematic than either the Canon or Nikon 70-200mm F2.8s, so here the Tamron does well. However, with the sun placed just outside the frame at 200mm, the lens fails badly, with bright veiling flare obscuring practically the entire image. However it's important to bear in mind that these examples are somewhat manufactured 'torture tests', and are not exactly typical of common shooting situations.
|70mm F16, Canon EOS 5D||200mm F5.6, Canon EOS 5D|
Background Blur ('bokeh')
One genuinely desirable, but difficult to measure aspect of a lens's performance is the ability to deliver smoothly blurred out-of-focus regions when trying to isolate a subject from the background, generally when using a long focal length and large aperture. Here the Tamron generally produces pleasing, smooth bokeh, especially with macro subjects. Even with very 'busy' backgrounds it does a good job of not detracting from the subject.
|200mm F3.5, Canon EOS 5D||200mm F2.8, Canon EOS 5D|
|50% crop||50% crop|
Our studio tests indicate lateral chromatic aberration to be very low with the 70-200mm F2.8 Macro, and indeed it is very rarely an issue in real-life. In fact it only ever really shows up at the extremes of the zoom (with none whatsoever in the middle of the range), and even then is scarcely a problem. These examples show 'worst case' scenarios, with visible, but far from critical red/cyan fringing at 70mm, and very faint read/cyan fringing at 200mm.
|70mm F8, Canon EOS 5D||200mm F5.6, Canon EOS 40D|
|100% crop, top left corner||100% crop, top right corner|
One problem we encountered with this lens in real-world shooting was a higher than expected proportion of slightly defocused images, especially visible when shooting at F2.8 where the depth of field can be extremely shallow. This was not a systematic 'front-focus' or 'back-focus' problem, but instead an apparently random tendency to miss focus slightly in situations for which we would normally expect a 100% hit rate. This issue persisted across a variety of camera bodies, from the EOS 450D through to the EOS-1D Mark III, so we can only conclude that it is a problem with the lens itself.
Below are a series of 100% crops from the centre of the frame shot using an EOS 5D at 200mm F2.8, using autofocus to re-focus each time (this is a distant subject, at about 275m/900ft). Of eight sequential shots taken in consistent bright sunlit conditions (1/1600 sec F2.8 ISO 100), half are clearly misfocused, and another slightly soft, although still usable. Now it must be stressed that 200mm F2.8 is the worst casr scenario, and reliability at other focal lengths and apertures will be better, but this isn't really the kind of focus accuracy we'd feel able to rely on for critical shots.
To investigate the issue further, we set up a controlled focus test under studio conditions. Here we used a different camera (EOS 40D), to rule out the camera body itself as the source of the focus problem. The camera was mounted on a tripod, using a cable release and mirror lock-up to eliminate any vibrations. The lens was refocused to infinity between each shot, then focused using AF; the subject distance was about 6m/20ft. Here the success rate (in rather lower light; 1/60s F2.8 ISO 100) was slightly lower, with only four of ten shots properly focused, as shown by the 100% centre crops below.
The test was repeated using the Canon 70-200mm F2.8 L IS USM on the same camera body, which gave all ten shots in correct focus (and focused considerably more quickly) - again 100% centre crops are below.
It's important to emphasize that we only have the Canon mount lens available to test, and the lens may well behave better on other makes of camera body (indeed this may even be a defect specific to our individual sample). But unfortunately it does seem unreliable on all of the bodies used during this review (i.e. EOS 450D, EOS 40D, EOS 5D, EOS-1D Mark III), so Canon users seeking absolute focus reliability wide open may well need to look elsewhere.
Sep 2, 2008
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