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10-26-2009, 08:58 AM   #1
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Tamron teleconverter will it work with newer lenses

Question for everyone,

Would this teleconverter work with the newer Pentax lenses? I did a search thru the lens forum and was not finding anything. I might not have gone far enough back. It seems that there are quite a few different brands, models, etc. I found one on ebay but they are calling it a rare find! Of course you can't always believe everything on ebay...

I want to make sure I make an educated purchase and get the best one that will with work the newer sdm lenses.

""Tamron 1.4x MC4 TC""

As always thank you to everyone for your insight...

10-26-2009, 11:25 AM   #2
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Maybe called a "rare find" because you can never find one for sale when you need it. The Tamron-F 1.4x Pz-AF MC4 (thats the full name on the sides of the TC) is the only Tamron TC that supports SDM I believe. Most TCs from other brands do not support SDM but there are exceptions.
10-26-2009, 11:35 AM   #3

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QuoteOriginally posted by imtheguy Quote
The Tamron-F 1.4x Pz-AF MC4 (thats the full name on the sides of the TC) is the only Tamron TC that supports SDM I believe.
The support for SDM lenses is spotty at best.

I have a copy of the Tamron TC in question. With the Pentax DA* 50-135mm, it hunts back and forth around the focus point on half press, then if I remove my finger from the shutter release and immediately half-press again, it achieves focus. I wouldn't call that "working." It works with my Sigma 150-500mm F/5-6.3 at 150mm, but does not at 500mm. Maybe because the combination is too slow at 500mm. But it works OK (albeit slow and needing something contrasty to lock focus on) with my screwdrive autofocus Tamron 18-250mm at 250mm (F/6.3).

I don't think there is any TC that works reliably with all SDM lenses.

This thread has some info.
10-26-2009, 12:28 PM   #4

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Hi stl09,

I'll agree with SOldBear on SDM compatibility

Here's a very long thread where a lot of TC owners related their experience, and what I got from it was there was no definitive answer for what might work with SDM.

With your lineup of telezooms, AF with the K20 will be spotty. Both the 80-320 and 50-200 are f5.6 at the long end and the 18-250 is f6.3. Add the one stop lost by a 1.4x TC and you'd have f8 and f8.8 as your max effective Av respectively, and the K20 will struggle to AF at these apertures in less than optimal lighting, but you can use them as MF lenses at the longer FLs, and many people do.

Another problem is that TCs will degrade IQ. This will be more noticeable with most zooms, with the possible exception of some "pro" grade constant aperture f2.8 or f4 zooms. The rule of thumb is the better the optical quality, the better a good TC will work.

The only available TC that will AF reliably with just about any lens (including SDM, but limited to max apertures of @ f4.5 or faster with the K20 and maybe f5.6 or faster with the K-7) is the Pentax F 1.7x Auto Focusing Adapter, but that's a unique (and for some time now, expensive) TC in that it allows AF (usually with limited focusing range) with any lens.


10-26-2009, 06:21 PM   #5
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QuoteOriginally posted by stl09 Quote
I found one on ebay but they are calling it a rare find! Of course you can't always believe everything on ebay......
Ha ha, there is almost always at least one or two of those on ebay at any one time - almost always listed as 'a rare find - new in the box'. Someone must have bought a crate of them when they were being discontinued and is now selling them one at a time at a tidy profit.
10-26-2009, 06:40 PM   #6
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The TC is not designed to work with AF lenses of f/5.6 or darker.
So forget about trying to use it on a consumer telezoom like a DA 55-300 or one of the 70-300s.

There is a lot of info about it on this thread:

Overall, it functions with the SDM lenses, but works poorly with the Sigma 70-200 HSM. Haven't got any other long SDM/HSM lenses to know if it works well with them, but one user mentioned using it with the DA* 200 with good success...

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