Sample crops from the centers, mid-sections and corners.   The APS-C section using the Sony A700 is first, followed by the full frame results.   Tamron 70-200mm F/2.8 @70mm   Reference image for crops below.  The mid-section and corner crops come from repositioning the subject in the frame accordingly.  Subject is about 400' (122m) away.   70mm               Center           Mid-section              Corner F/2.8 F/4 F/5.6 F/8 F/11   The 70mm performance is pretty good, with a slight lack of contrast at F/2.8, but looking very good at F/3.5 to F/4.  The mid-sections are almost as sharp as the centers.  As you move towards the corners, the sharpness drops a little, but more noticeable is the color fringing, (mostly magenta).  This type doesn't go away as you stop down, that's why it's visible at all apertures.   Exposure differences in the corners are from light fall-off.   135mm   Tamron 70-200mm F/2.8 @135mm   Reference image for crops below.  Subject is about 500' (152m) away.   135mm               Center           Mid-section              Corner F/2.8 F/4 F/5.6 F/8 F/11   With the lens zoomed to 135mm and using a wide-open aperture, you'll see a slightly soft image, but stopping down to F/4 makes a big difference, and the mid-sections are as sharp as the centers.  The corners are pretty sharp too from F/5.6-11.   200mm   Tamron 70-200mm F/2.8 @200mm   Reference image above, subject is about 700' (213m) away.   200mm               Center           Mid-section              Corner F/2.8 F/4 F/5.6 F/8 F/11   When near the long end, the image is a little soft at F/2.8-3.5, but sharpens up nicely at F/4.  The mid-sections are pretty sharp stopped down, with the corners looking almost as good.    ____________________________________________________________________________________________________________________________________________________________   Sharpness crops using the full frame A900.   Below are crops from a test chart, in this case a magazine cover.  Lens to subject distances average about 20' (6.1m).  Atmospheric conditions were not optimal during the full frame testing period, so I had to resort to indoor shooting, although this focusing distance is what you might find at an indoor concert or portrait session.       70mm               Center           Mid-section              Corner F/2.8 F/4 F/5.6 F/8 F/11   A good performance at 70mm, and similar to the APS-C crops above.  I see a very acceptable image at F/2.8, and a very good image at F/4-8.  There is some noticeable magenta color fringing in the corner crops, but not really showing any more than what you see with the APS-C corner crops above.   135mm               Center           Mid-section              Corner F/2.8 F/4 F/5.6 F/8 F/11   The whole image looks sharp at F/5.6-11.  The mid-sections and corners respond well to closing the aperture a couple of stops, but have plenty of resolution at F/2.8-4 if you look past the minor veiling haze.   200mm               Center           Mid-section              Corner F/2.8 F/4 F/5.6 F/8 F/11   I see the same basic results here as with the 135mm crops, meaning a little soft at F/2.8, but sharpening up at F/4, where the whole image begins to look pretty darn good, especially for a full frame camera.  The corners are not quite as sharp as the mid-sections, and don't seem to quite match the 135mm results, but they're still very acceptable.  There is a tiny bit of color fringing noticeable (purple along the palm fronds) in this scene.  Exposure differences in the corner crops are from light fall-off.   Back to the Tamron 70-200mm F/2.8 standard review section