UWA = ultra wide angle.

i also like to call it UWA is cos when people who haven't used it before will say "uuuuuwwwaaaaaaa!!!"

such lenses usually go from 10 to 24 range for APS-C body.

eg Canon EF-S 10-22

for Full Frame body, their UWA are like EF 17-40L / EF 16-35L.

the EF 17-40L / EF 16-35L on APS-C body works like short zoom range.

The EF-S 10-22 cannot be used on Full Frame bodies since they only accept EF lenses, not EF-S lenses.

the APS-C body on the other hand accepts both EF and EF-S lenses.

*sure got more questions to come. LOL. i let others answer, now i go play game!

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Added on June 7, 2010, 1:32 amtook this in AFC Studio, Singapore using my Sigma 10-20 UWA....... i think the fella dying liao, or maybe the HSM dying.