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05-30-2010, 06:17 AM   #16
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The limit of compatibility is onlyy the300f2.8 and bigger faster lenses.

The sigma tc'sare not general purpose tcs

05-30-2010, 01:09 PM   #17
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QuoteOriginally posted by Lowell Goudge Quote
The limit of compatibility is onlyy the300f2.8 and bigger faster lenses.

The sigma tc'sare not general purpose tcs
So it will only work with the bigger faster lenses or those are the lenses it won't work with?
05-30-2010, 02:15 PM   #18
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QuoteOriginally posted by littledrawe Quote
So it will only work with the bigger faster lenses or those are the lenses it won't work with?
Hi littledrawe,

The compatibility problems with Sigma TCs are either physical incompatibility with lenses that don't have recessed rear lens elements (it physically can't be mounted), or electrical incompatibility (Sigma TCs don't have SDM electrical contacts) so even if SDM/HSM lenses can be fitted, the AF system won't work, so would only be MF -- or both, of course.

The only AF lenses that will AF reliably with Sigma TCs are screw drive lenses with a recessed rear element and a max aperture of faster than f8 including the multiplication factor of the TC (you have to multiply the max aperture of the lens by the magnifying factor of the TC to get this) -- there may be some exceptions, but that's a pretty reasonable rule of thumb I'd think. . .

Scott
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