Originally posted by C.W Tsorotes It is a pitty that it does not perform that well at the long end.
See this text from Slrgear.com:
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Sharpness
The 120-400mm is a fairly sharp lens, but its performance is optimized for the wider range of its focal length spectrum. As you zoom in towards the 400mm range, image sharpness degrades significantly. Optimal image sharpness was achieved at either 120mm and ƒ/5.6, or 150mm and ƒ/8.
Wide open and wide-angle (120mm, ƒ/4.5) image sharpness is quite good, with test results showing 1.5 blur units across the frame. Stopping down to ƒ/5.6 improves central sharpness to 1 unit, but there is still some very slight corner softening. Diffraction limiting seems to set in at ƒ/11, but image quality never gets so bad, reaching 2.5 blur units at ƒ/22. Results at 150mm are almost the same, just a tad less sharp.
However, at 200mm and above, image sharpness starts to worsen. Our sample copy of the lens also showed some centering issues at this focal length. Sharpness showed results of between 1-2 blur units in a very small central region, while corner softness reached 4.5 blur units; as the lens is stopped down, quality improves dramatically at ƒ/8 and ƒ/11 (1 blur unit centrally, 2-3 units in the corners) and the image is generally soft at ƒ/25 (3 blur units).
Between 300 and 400mm, performance when used wide open (ƒ/5.6) is nothing to write home about - very uneven and soft (3-5 blur units at 300mm, and 5-8 units at 400mm).
Stopping down to ƒ/8 or ƒ/11 is necessary to get any kind of sharpness out of the lens at this focal length. Interestingly, image sharpness is better at ƒ/22-29 than when used wide open at these focal lengths.
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I think my DA*60-250mm + 1.7TC is still a good alternative.
As soon as Sigma delivers telezooms that are optimized for the long end, I'll get one.
- Bert