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Old Oct 12, 2003, 9:11 AM   #1
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Default Canon USM / Sigma HSM ??

Does one system perform better than the other (focusing speed, focusing noise-level, lock-on focus accuracy)? Would it perform differently if comparing an EOS-10D to an EOS-300D?
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Old Oct 12, 2003, 11:06 AM   #2
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There is 3 different types of USM. Not all are created equal. I could probably dig up the posts (I think I saved them) from another forum listing which lens is which type. I don't know enough about HSM, but some of them are quite fast, from what I've been told. I have never heard one, so I can't comment on the noise.

The last one (lock-on focus accuracy) isn't really a feature of the USM/HSM. Its effected by:
1) Camera body. Better AF system, better focus accuracy.

1) Lower max fstop. The lower the fstop, the more light the AF system gets to work with. This doesn't always matter (some times its a bright, well lit day) but other times it makes all the difference in the world.

Probably other things as well, but those come to mind.

Eric
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