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05-31-2010, 06:56 AM   #1
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70-200mm with Quantum 2x tele vs . . .

I came to Pentax with my K20D, but I've always had a lot of respect for the brand. I am little frustrated that Pentax zooms top out at 250mm (as many have said before). So this is what I'm looking at, I just bought a Quantum 2x teleconverter which looks like it has the contacts for the SMD / HSM function (actually for the older power zoom functions, I think).

Can I use this (AF) with the Pentax-mount Sigma 70-200mm HSM 2.8?
(wish the Sigma teleconverters worked with HSM )
If not, does anyone know how well the Tamron 70-200mm 2.8 works with a 2x?

My only other reprieve would be to buy a Sigma 150-500mm HSM. I would like the HSM function if at all possible just for the quiet focusing to not scare birds (what I'll be shooting).

I rarely print larger that 11x14 in, so that will give you an idea what sharpness I need.

Thanks for any help!

05-31-2010, 01:21 PM   #2
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I don't think any current tc works in AF with Sigma HSM. you have to go manual. The kenko2xtc and promaster 1.7tc would autofocus on my Tamron 70-200mm f2.8. the image quality was good-very good.
05-31-2010, 02:48 PM   #3
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QuoteOriginally posted by ivoire Quote
I don't think any current tc works in AF with Sigma HSM. you have to go manual. The kenko2xtc and promaster 1.7tc would autofocus on my Tamron 70-200mm f2.8. the image quality was good-very good.
I was kinda afraid of that. Does anyone have a second experience that Sigma HSM + TC does not work?

Unfortunately the 60-250mm is not fast enough with a 2x TC to keep AF.

How was your Tamron for noise while focusing? Did you find it quick enough with the TC?
06-03-2010, 01:19 PM   #4
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Any more information / ideas on this topic?

I'm really trying to decide between a 70-200mm f2.8 vs a 150-500mm / 120-400mm.

06-03-2010, 06:57 PM   #5
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QuoteOriginally posted by Thrasis Quote
Any more information / ideas on this topic?

I'm really trying to decide between a 70-200mm f2.8 vs a 150-500mm / 120-400mm.
Those are sort of different lenses - first one is constant aperture, second and third are significantly longer. I have the first one, but still plan on getting the second one to complement it.
06-03-2010, 07:02 PM   #6
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I think he is considering 70-200mm f2.8 + 2x tc vs those two. I think there are many some of the Tamron 70-200mm f2.8 with a 1.7x or 2.0x tc if he searches around.
06-03-2010, 07:10 PM   #7
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Currently, there is NO 2X TC that works (autofocus-wise) with HSM or SDM lenses.
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