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08-07-2011, 03:18 PM   #1
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Sigma 70-200 2.8 (NON-HSM) + Sigma/Kenko/Pentax TC?

Hi all,

I am looking for a TC to complement my Sigma 70-200 2.8 (DG but non HSM macro). I want a 1.4 or 1.5x teleconverter. I have read about the Sigma, which does not work with the HSM version but should work with mine. What about the kenko 1.5x. Is it any better? I think the Pz version is well known becasue it works with the HSM versions of the Sigma...but can I go with the regular Kenko 1.5x? How does it compare to the Sigma?

Thanks beforehand

08-08-2011, 08:02 AM   #2
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I've never used the Sigma teleconverters, but I have three other Pz-AF teleconverters (1.5x, 1.7x, 2.0x) From what I understand Sigma's 1.4x teleconverter only fits with certain lenses, such as your Sigma 70-200mm f/2.8, due to the number of elements/physical design of the teleconverter. I get the impression the results are very good when you match up a Sigma teleconverter with a compatible Sigma lens. Since you have a non-HSM Sigma lens, you can use Sigma teleconverters and retain lens AF on Pentax.

I think the only advantage you'd have with a Pz-AF teleconverter (Kenko, Tamron, etc.) is you'd be able to use it with a broader range of lenses, and sort of retain HSM/SDM (it will kind of work, but not as well since it was designed to pass Power Zoom not HSM/SDM, and works only with some lenses according to reports... I don't have any HSM/SDM lenses, so I don't have any first-hand experience with them and my Pz-AF teleconverters).

Some people like to bypass the whole HSM/SDM issue by getting the Pentax-F 1.7x AF teleconverter, where you manually focus the lens most of the way and then can have the teleconverter do the final AF itself (i.e. doesn't matter if the lens is AF or not, you never use the AF capability of the lens with that teleconverter). It's pricey though, often $300.
08-08-2011, 10:02 AM   #3
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Thanks nater,
yes, I have been checking the pentax too, but lately it is like $400 and $500
I was asking about he non Pz version of the Kenko because it is much cheaper. I would not mind not being able to use it with other lenses but I would like to make sure it works with the sigma 70-200 (non HSM) and the quality is similar to the sigma.
anyone who has the answer to these questions?
08-08-2011, 03:18 PM - 1 Like   #4
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QuoteOriginally posted by sergysergy Quote
Thanks nater,
yes, I have been checking the pentax too, but lately it is like $400 and $500
I was asking about he non Pz version of the Kenko because it is much cheaper. I would not mind not being able to use it with other lenses but I would like to make sure it works with the sigma 70-200 (non HSM) and the quality is similar to the sigma.
anyone who has the answer to these questions?
No question that the Kenko 1.5x TC will work with the Sigma 70-200mm non-HSM f/2.8 (I say this because the Sigma 1.4x TC works and that will protrude slightly into the lens and the Kenko does not).

Chances are the Sigma will be better quality for three reasons:

1. Sigma 1.4x is a 5 element TC (Kenko 1.5x is a 4 element)
2. Sigma 1.4x is APO (apochromatic) and should be better corrected against chromatic aberrations (Kenko is not APO)
3. Sigma 1.4x protrudes slightly into lens body (when it's possible to use TCs with this design combined with a telephoto lens the results tend to be better)

How much better will need someone who has tested both TCs with this lens to chime in...

08-08-2011, 03:31 PM   #5
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ok, you convinced me...I will go for the Sigma!
thanks a lot for the detailed reasoning
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