Studio Tests - 35mm full-frame format
The 70-200mm F2.8 G puts in a very good showing on full frame. Direct comparison of our sharpness data between it and the two third party lenses from Tamron and Sigma is complicated by the very different resolutions of the test bodies (A900 vs Nikon D3 and Canon EOS 5D). However it seems fair to conclude that the Sony is the best performing of the three lenses, although perhaps not by very much.
Sharpness is extremely high in the center even wide open, although it drops off towards the extreme corners (which sharpen up progressively on stopping down). The central zone of very high sharpness at F2.8 decreases progressively in size at longer focal lengths, disappearing entirely at 200mm, although sharpness is still very good and even across the frame. Overall, best results are obtained between F4 and F11.
Chromatic aberration is generally low. At 70mm there's a little green/magenta fringing, but it's a bit less visible than on APS-C. The strongest CA is at 200mm , where we see green/magenta to a similar level as on APS-C.
We consider falloff to become perceptible when the corner illumination falls to more than 1 stop below the center. Falloff is pretty well average for the class here, ranging between 1 1/3 stops and 2 stops wide open, although unusually it's at its worst at 100mm. As expected it decreases on stopping down, and essentially disappears at F5.6.
Distortion is reasonably low, ranging from 1.4% barrel at 70mm to -1.3% pincushion at 200mm. This may, just occasionally, be visible in normal shooting, but is unlikely to have any real negative impact.
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 1.5x larger, MTF50 should therefore be 1.5x 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.
Like most 70-200mm F2.8 lenses, the Sony is prone to giving extensive flare patterns with bright light sources in the frame. As usual these become increasingly defined on stopping down, but at no point can they be considered to be anything other than highly destructive to the image. On the other hand, the lens behaves pretty well when there's a strong light source just outside the frame but still impinging on the front element, maintaining contrast impressively well (see sample below right).
|70mm F2.8, Sony Alpha 850||70mm F8, Sony Alpha 850|
|70mm F22, Sony Alpha 850||200mm F2.8, Sony Alpha 850|
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. On the whole the 70-200mm F2.8 G produces very pleasing bokeh across a wide range of real-world shooting conditions - we'd consider it one of the nicer fast telezooms in this regard. About the only time it trips up is when faced with complex distant backgrounds, and shot slightly stopped down, at which point the bokeh can look a little harsh.
|200mm F4, Sony Alpha 700||200mm F4, Sony Alpha 850|
|50% crop||50% crop|
Lateral chromatic aberration is on the whole low, but fringing can still be visible on high-contrast edges towards the corners of the frame. It's most obvious the long end of the range, but there's also a little visible at 70mm if you look hard enough. The samples below illustrate what you might expect to see in actual use; the fringing is red/cyan in color at 70mm, and green/magenta at 200mm. But even looking at a 100% crop from the 24Mp Alpha 850 it's not hugely objectionable - you'd have to make a very, very large print indeed to see it.
Sony Alpha 700, 70mm, F4
Sony Alpha 850, 180mm, F5.6
|Camera JPEG||Camera JPEG|
|100% crop, lower left||100% crop, lower right|
Longitudinal chromatic aberration (color fringing around high-contrast edges in front of, and behind the plane of focus) can very occasionally be seen if you look really hard for it, but generally has little impact on practical use.
|200mm F4, Sony Alpha 850||100% crop|
The 70-200mm F2.8G has a fairly impressive closest focus distance of 1.2m (although that's not quite as close as its Tamron and Sigma rivals), but as mentioned earlier its image quality at such close distances can leave something to be desired. It's extremely soft at F2.8, and really needs to be stopped down to about F5.6 to reach decent levels of sharpness. In the process, the focus shifts substantially away from the camera, so achieving critical manual focus (for example using magnified 'Manual Focus Check' live view on Sony's latest DSLRs) can be rather difficult.
The graphic below illustrates this, using 50% crops from the center of the frame with the lens set at 200mm and a focus distance of 1.2m, using the 12Mp Sony Alpha 700. At F2.8 the whole image is simply soft and muddy, with scarcely any low-contrast detail; the second matchhead from the right is the point of focus. Stop down to F5.6 and it's as if a veil has been lifted from the scene - contrast has increased significantly and fine detail is well-resolved - however the focus has shifted to the third matchhead. Stop down further to F11 and there's a further increase in contrast in the in-focus regions, with possibly a slight shift in focus further away from the camera.
|200mm F2.8||200mm F5.6||200mm F11|
Some real-world examples of macro shots at 200mm F2.8, on both APS-C and full frame, are shown below. In both cases 100% crops are taken from in-focus regions.
Sony Alpha 700, 200mm F2.8
Sony Alpha 850, 200mm F2.8
|100% crop||100% crop|
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