In article <googlegroups.com>,
Siddhartha Jain <co.uk> writes
The most meaningful test is does it give good results in the kind of
photography you do. However, to ensure you are testing the lens, use a
tripod, otherwise you might just be testing the steadiness of your hand.
Use slide film if using a film body. Ensure you check the performance
wide open as well as at mid-apertures.
Your main problem will probably be that you do not have any reference
standard - unless you have one or more "known-good" lenses. Get a
better-equipped friend to help.
It is a little surprising to see someone buying a lens from a maker
whose quality control they have such doubts about. I guess you must have
price constraints. I have bought 3 Sigma lenses in the past and was not
over-impressed. The 14mm was just about good enough - and a fraction of
the price of the Canon offering - but does not work on my 10D. I vowed
not to buy another (though I must say the 12-24 looks a bit tempting).