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02-26-2011, 10:19 AM   #1
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Sigma 2x Teleconverter for Tamron 70-200mm f/2.8

Hi all,

Does anyone know if the Sigma APO 2x teleconverter will work with the Tamron 70-200mm f/2.8 lens? I am trying to sell my TC and a potential buyer asked me if I knew. I know autofocus would work since the Tamron is screwdrive and not BIM. Does anyone know if there is enough room behind the rear element of the lens to fit the Sigma 2x TC. Thanks in advance for any guidance.

-Mike

03-01-2011, 02:37 AM   #2
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I'm afraid it is not. Sigma makes this stuff deliberately not to be compatible in electronics and communication protocols. So if he uses it, he will probably have to use manual exposure and enter the focal lenght manually for the SR.
03-01-2011, 05:29 AM   #3
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While echo_cid correctly states the TC from sigma will not work on the tamron lenses, the rest Of his post is way off base

Sigma TCs first of all are not designed for hsm just screw drive. Second the optical design has a protruding front element that only suits a very limited number of long fast sigma lens designs
03-01-2011, 06:23 AM   #4
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OK thanks for correction. I don't know all the details but this thread was long time unanswered. When I tried my AF1.7x TC with Sigma lenses it didn't work correctly (only manual exposure possible using aperture ring on lenses). I asked for the possible reason on other forums and was told that Sigmas TC are not electronically compatible with other lenses and vice versa.
With my bad experience with Sigma lenses compatibility with Canon or Pentax early A-bodies I did believe the Sigma really does this on purpose.

03-01-2011, 11:47 AM   #5
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QuoteOriginally posted by elho_cid Quote
OK thanks for correction. I don't know all the details but this thread was long time unanswered. When I tried my AF1.7x TC with Sigma lenses it didn't work correctly (only manual exposure possible using aperture ring on lenses). I asked for the possible reason on other forums and was told that Sigmas TC are not electronically compatible with other lenses and vice versa.
With my bad experience with Sigma lenses compatibility with Canon or Pentax early A-bodies I did believe the Sigma really does this on purpose.
Your comment about the AF TC is a surprise, it should work with the sigma lenses, giving all exposure modes, unless you had a bad contact.

the compatibility as far as I know is not so much electric, and if you were told that you were misinformed. I appologize on behalf of the forum for that.

the issue with sigma TCs is mechanical compatibility. DUe to the protruding front element of the TC, the TC will only mount to lenses that have a 35mm diameter, 12mm or greater recess at the rear before any mechanical or lens parts. In fact, even though it will go onto the BIGMA, you can't either focus to min distance, or zoom out all the way to 50mm (i forget which) because to do so, causes the rear element to go back and hit the TC.

I once posted the contents of the sigma compatability chart that came with my 1.4x and 2x TCs, there were a few pentax lenses, like the 300F2.8, 400F2.8 etc, plus the big sigma lenses.,
03-01-2011, 12:37 PM   #6
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Yes, I own the Bigma so I do know. There is a zoom limiter so it cannot be zoomed under ~100mm.
I borrowed my AF1.7x to a friend and I cannot clearly remember what was the problem. I'll add details when he returns.
But for sure my Sigma 180mm macro (great lens otherwise) does not report aperture correctly to my SuperProgram and SuperA bodies. It reports f1.2 speed. I guess they didn't implement the backward compatibility. That may by also the problem of the AF1.7 TC which is also quite old.
03-02-2011, 08:56 AM   #7
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QuoteOriginally posted by elho_cid Quote
Yes, I own the Bigma so I do know. There is a zoom limiter so it cannot be zoomed under ~100mm.
I borrowed my AF1.7x to a friend and I cannot clearly remember what was the problem. I'll add details when he returns.
But for sure my Sigma 180mm macro (great lens otherwise) does not report aperture correctly to my SuperProgram and SuperA bodies. It reports f1.2 speed. I guess they didn't implement the backward compatibility. That may by also the problem of the AF1.7 TC which is also quite old.
Note that the AF 1.7x tele converter reports or should report apertures corrected for the addition of the teleconverter back to the camera body.

However, having just tried this with my sigma 70-200F2.8, it is really strange, the lens still reports F2.8 to the camera even through the pentax TC, where as all my other lenses when used with the 1.7x AF TC, report the correct (or much closer to correct )aperture.

My 85F1.4 shows up as F2.8, mt 8mm F3.5 shows up as F5.6, my pentax 28-80F3.5-F4.5 shows up as F6.7. SO the TC is correcting for all these lenses BUT not the sigma. This makes me think the issue is allignment of the contacts or something.
03-03-2011, 03:59 AM   #8
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Thanks for verifying on your side.
It makes me think that Pentax probably changed the way of aperture reporting between A and FA. While Pentax products do keep backward compatibility (even DA lenses report aperture correctly to old SuperProgram) Sigma only implemented the new protocol. And the AF1,7 was designed primarily for A lenses, so it expects old protocol on the lens side.
I guess the Sigma lens reports f1,2 to it as it does to the SuperProgram.

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