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03-25-2014, 08:53 PM   #1
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Compatibility issues with old AF bodies, Sigma lenses?

I recently got an SF1 body. I have an ME Super as well, but I'm coming back again from Nikon-land got used to shooting an N90 and intended this as a replacement. I do appreciate AF/AE for walk-around and city shooting where I want to squeeze off a shot without fiddling.

Funny thing is that I have a Sigma 24-70 that will not autofocus on this body. It works fine on my K10D so I can eliminate a physical problem with the lens, and I have a Tokina 19-35 that focuses on the SF1 which likewise should a problem with the body. The Sigma's auto aperture does work correctly on the SF1.

Are there any known compatibility issues with old KAF bodies and Sigma lenses? I've searched here and haven't come up with anything. My previous understanding was that KAF is KAF and hadn't previously heard of any Canon-style compatibility problems with third party lenses.


03-25-2014, 09:01 PM   #2
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Is the Sigma the HSM version? Some lenses have both the internal focus motors and the screw drive, but I don't believe the Sigma does. If it doesn't have the screw drive it won't auto focus with anything older than the K10D/K100D Super.
03-25-2014, 09:02 PM   #3
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Thanks for the reply, good question. This one is screw drive only.
03-25-2014, 09:37 PM   #4
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If it is screw drive then it should work with no problems at all. I have an sf1 and all my screw drive lenses work fine on it.

03-25-2014, 10:49 PM   #5
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Sigma lenses have had compatibility issues with most brand of cameras, but usually it's about older lenses having problems on newer cameras.
But that's probably because that is more common to use old lenses on new cameras.

My guess is that the Sigma 24-70 is not recognized as a AF lens by SF1. Which might be because of a the firmware in the lens is not 100% compatible with older cameras.
03-25-2014, 11:17 PM   #6
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I find that some sigma lenses do not engage the screw drive correctly on film bodies. I had this problem with my 70-200/2.8 I think it has to do with the orientation (I.e. angle) of the screw drive, where my DSLRs leave it at a different angle than the SLRs once engaged and working, it was ok until I put it on my DSLR then it was hit and mis until it engaged the drive.
03-26-2014, 11:07 AM   #7
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Thanks - makes most sense to me that this would be a physical compatibility issue with the screw drive. I can spin the focus ring after mounting and get the ring to "lock" into place as expected, but that doesn't mean much.

Is there a pin/pins on the lens mount that tells the camera if AF is present? There must be, or the focus drive would whack back and forth with an M lens and AF selected on the body. Anyone know what it is? Electrical, physical?

I could easily be wrong, but I wouldn't have thought that the old-style KAF lenses contained any real firmware. Whatever logic needed for a focus decision is in the camera, isn't it?
03-26-2014, 03:58 PM   #8
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The K-AF lenses had the 7th electronic contact (A mount lenses/bodies only have six contacts) - which did at least pass the focal length - the film AF SLRs warned if the lens was wider than the built-in flash coverage. This worked with zoom lenses too. You could try cleaning the contents on camera & lens.

I'm still surprised my Z-1 & K-5 can focus my '90s Sigma 70-300 Apo Super screw-drive lens. Not only is the focus ring the 'wrong' way round (infinity on the right), but the screw-drive coupling spins the 'wrong' way to infinity as well.

03-26-2014, 04:28 PM   #9
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Thanks for the helpful information.

I've cleaned contacts on lens and body and checked again just to make sure I'm not crazy - the body drives the Tamron 19-35 and the 18-55 DA (!) just fine, but will not autofocus the Sigma. Likewise, the Sigma still focuses just fine on my K10D.

I guess I'm gonna punt and unload the 24-70. It's a real useful range for a walk-around, but only makes sense to me on FF. If it's gonna be MF only, I'd just as soon walk around with a 28/2.8. This is the 24-70/3.5-5.6 by the way, not the constant 2.8, so no great shakes.

Still wish I understood the problem, though.


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