Tamron 18-200mm corner sharpness, tested with Nikon D2X
To measure corner sharpness we photographed
the Enhanced Digital Camera Resolution Chart with each lens using a Nikon
D2X. The D2X was set to Large Fine JPEG mode,
optimised for quality rather than size, and with A for Image Sharpening
and Tone Compensation.
Each lens was tested at its widest and longest focal lengths and with various
apertures selected in Aperture Priority mode. The crops are taken from the lower
left corner of the chart and presented here at 100%. The 18mm crops show
a larger area of the chart because minimum focusing distances forced us
to shoot it from further away.
At the 18mm wide angle end, the Tamron noticeably outperforms the Sigma in the far corners, although both are beaten by the Nikkor; note the Tamron and Sigma results improved considerably just a short distance in from the
extremes. The story is similar at the 200mm telephoto end, with the
Tamron beating the Sigma, but the Nikkor again comfortably out-performing both.