Tom writes:
> I've inherited an old Nikon N6006 with a Sigma autofocus 28-105mm
> 1:4-5.6 (58 mm dia) lense. If I buy a Canon EOS 20d, can I use this
> lense on this Canon body?
Probably not. Even if it were an EOS mount Sigma lens, maybe even
not then.
I have the EOS mount 70-210 f/2.8 and 28-70 f/2.8 Sigmas purchased in
1993ish and neither works on post Elan-II era bodies (my 300D for
instance). They give ERR99 because Canon changed the signalling
protocol for aperture stop down, and Sigmas reverse engineering of
that protocol (rather than licensing it) was successfully foiled.
As such, I can only use these lenses on aperture priority mode wide
open (f/2.

. Later model Sigmas may be chip upgradeable. Mine were
not however.
Throw in the fact that you in your case would somehow need to get
these Nikon mount Sigmas to even fit on the EOS mount, odds are slim
to none that it'll all work in the end.
For more info on the EOS issue, see FAQ #7 here:
http://sigmaphoto.com/faq/faq.asp?navigator=3
Best Regards,
--
Todd H.
http://www.toddh.net/