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02-06-2009, 07:13 AM   #1
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Why don't some AF lenses work with SFX and SF7?

mods please move this thread to the appropriate forum if I screwed the location up.

http://www.sigmaphoto.com/news/news.asp?nID=3471

Quote from this article on Sigma's website:

AF function of Pentax mounts cannot be used with SFX / SF7 Cameras.

Does anybody know why that is?

02-06-2009, 01:18 PM   #2
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QuoteOriginally posted by ftpaddict Quote
mods please move this thread to the appropriate forum if I screwed the location up.

http://www.sigmaphoto.com/news/news.asp?nID=3471

Quote from this article on Sigma's website:

AF function of Pentax mounts cannot be used with SFX / SF7 Cameras.

Does anybody know why that is?
SIGnificant MAlfunction
02-06-2009, 01:50 PM   #3
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I can't be positive on this, but I read somewhere that the format / protocol of the data transmitted over the data pin has changed from time to time on the KAF mount.

This is somewhat confirmed by people who have Kenko (I believe) teleconverters, that while they have the KAF2 mount from the days of PZ-1 don't correctly feed lens information from SDM lenses back to the body.

This teleconverter has electronics in it that translate the apature and focal length data to correct for the converter. There was a thread about someone bypasing these electronics to make the TC or more specifically AF work on SDM lenses.

It may be that sigma has decided for new lenses, specifically digitally optimized, that no one is buying these for an SFx or SF7 body.

It may also relate to other things like missing apature couplings, ...
02-06-2009, 04:47 PM   #4
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There is also the often repeated rumour that Sigma doesn't actually pay licensing fees, and thus has to reverse engineer protocols rather than recieving the documentation.

If true, this could explain the random incompatabilities wth some Sigma gear.

02-07-2009, 01:52 AM   #5
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All of your explanations probably hold a bit of truth to them. Except for yours, Wheatfield. Some of their lenses are decent.
02-07-2009, 08:20 AM   #6
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QuoteOriginally posted by ftpaddict Quote
mods please move this thread to the appropriate forum if I screwed the location up.

http://www.sigmaphoto.com/news/news.asp?nID=3471

Quote from this article on Sigma's website:

AF function of Pentax mounts cannot be used with SFX / SF7 Cameras.

Does anybody know why that is?
Besides other explanations given, the exact point of that statement is that Sigma Lenses will not work the AF functions designed for the PZ10-20-1 and 1p cameras that did the "power zoom", "image size tracking" and "zoom colapsing to smalles size when camera turned off" functions.

Normal Autofocus "should" work fine, but as others said, Sigma well stands for SIGnificant MAlfunction, where not all the sigma lenses worked fine with all Pentax AF bodies. I've seen and known of some issues regarding jittery focusing, bad aperture information and such.
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