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07-28-2010, 02:29 PM   #1
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Is there a trick to getting Sigma's TCs to AF?

I just bought a Sigma 1.4TC from a forum member to use with my 100-300/4 and I'm having major problems getting it to AF. It has worked a couple of times. I've tried cleaning the contacts, using it outside in plenty of light, setting the aperture to 5.6 (and higher and lower) using both the aperture ring and the in-camera settings. My lens is clearly on Sigma's compatibility list, so what gives? It seems like the times it has worked is right after I have disassembled/reassembled everything, but even that doesn't work every time, not that that would be acceptable if it did. Surely someone with experience with these things knows what's going on.


Last edited by DogLover; 07-28-2010 at 02:50 PM.
07-28-2010, 05:59 PM   #2
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I use the 1.4x regularly on my 70-200. It does slow the focus down a tad. I find myself sort of pumping the AF button a bit to help it find the focus. But I do plenty of sports shots with it, so it can't be that bad. However your f4 lets in less light, so it probably would struggle a bit more than my 2.8 lens.
07-28-2010, 07:07 PM   #3
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I use a sigma 1.4x tc on my 100-300mm F4 I don't have any problems with AF even with a CPL on it. What happens when you half depress the shutter? Does it attempt to AF at all or does it not turn the screw?
07-28-2010, 07:11 PM   #4
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QuoteOriginally posted by birdoprey Quote
I use a sigma 1.4x tc on my 100-300mm F4 I don't have any problems with AF even with a CPL on it. What happens when you half depress the shutter? Does it attempt to AF at all or does it not turn the screw?
You can hear the motor either spinning wildly or shifting back and forth, but in either case nothing is actually happening to the focus. BTW, just to make sure it's not the lens, I removed the TC and the lens focused perfectly. Have you found that there are any specific aperture setting requirements when using the TC? I assume you can't use anything higher than 5.6.


Last edited by DogLover; 07-28-2010 at 07:33 PM.
07-28-2010, 08:01 PM   #5
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If you hear it spinning and you don't see a change in the view finder then maybe the screw drive connection is the problem. I've been able to AF at much higher than 5.6 depending on light conditions. I don't think aperture is the issue here, sounds like something physical/mechanical.
07-28-2010, 08:19 PM   #6
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Hmmm. OK, thanks. Anybody else know of anything specific that may be the problem?
07-29-2010, 04:17 AM   #7
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I have not had this problem on my DSLRs but on my PZ-1 I find it has difficulty picking up the screw drive.

Normally, the screw drive linkage is spring loaded and will slip as it rotates until it locks into the lens/TC, but for some reason on my PZ-1 it has trouble locking into the screw drive. I don't know if it an allignment problem or not but since I don;t use the PZ-1 often any more I don;t worry about it. It is probably an allignment issue

You may wish to mount the TC to the body first, and then mount the lens to the TC
07-29-2010, 04:44 AM   #8
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QuoteOriginally posted by Lowell Goudge Quote
I have not had this problem on my DSLRs but on my PZ-1 I find it has difficulty picking up the screw drive.

Normally, the screw drive linkage is spring loaded and will slip as it rotates until it locks into the lens/TC, but for some reason on my PZ-1 it has trouble locking into the screw drive. I don't know if it an allignment problem or not but since I don;t use the PZ-1 often any more I don;t worry about it. It is probably an allignment issue

You may wish to mount the TC to the body first, and then mount the lens to the TC
Thanks, Lowell. I think you're definitely right that it is a problem with the screw drive not engaging. I tried what you said and it worked....for about a second, then went back to misbehaving. That's what's odd about it. Seems like if it ever works, it should work for the rest of the time that it is mounted, but it doesn't. It has never worked for more than a few seconds.

07-29-2010, 01:19 PM   #9
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Remember, focusing is always done with the aperture wide open. So you should be able to AF at any aperture you like, as long as the maximum aperture of the lens is f/5.6 (and there's enough light for AF to work at all).
07-29-2010, 04:32 PM   #10
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I think you'll find thatit is spinning and occasionally catching but the spring is not strong enough to insert the "Tang"'pf the scree drive into the lens. Perhaps manually focusing and turning the lens Af drive will lock it in
07-29-2010, 06:07 PM   #11
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QuoteOriginally posted by Lowell Goudge Quote
I think you'll find thatit is spinning and occasionally catching but the spring is not strong enough to insert the "Tang"'pf the scree drive into the lens. Perhaps manually focusing and turning the lens Af drive will lock it in

Yeah, I did try that. I thought maybe if I got it close manually, it could "find its way." But it didn't work. There is just obviously something defective with it. The forum member that sold it to me agreed to a refund, so I've already sent it back. Thanks for trying to help, though.
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