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12-21-2008, 07:09 PM   #1
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Promaster 1.7x AF Teleconverter

Just got my Promaster TC and was wondering if folks who have used this TC, can list which lens they have used without problems ?

Particularly, interested in capatibility with lens I have:
  • Pentax SMCP-FA 50mm F/1.4
  • Sigma 10-20mm F/4-5.6 EX DC
  • Sigma 18-50mm F/2.8 EX DC Macro
  • Sigma 105mm EX DG F/2.8 Macro
  • Tamron SP AF17-50mm F/2.8 XR LD - i know works
  • Tamron AF70-300mm F/4-5.6 Di LD Macro 1:2 - i know works

Quick hand held snaps





thanks

George

12-22-2008, 04:51 PM   #2
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I have the Promaster 1.7, the PTX FA 50/1.4 and the Sigma 105 - they work togrther with no
problems..........
01-02-2009, 01:26 AM   #3
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thanks John for the info
01-02-2009, 04:50 AM   #4
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I do not have the Promaster tc, so I cannot comment on that particular product. But I have a large collection of tcs, all Pentax L and S modells, the two Sigma Apos and several Kenkos. I would none of these (even the best Pentax ones) use with:

* Sigma 10-20mm F/4-5.6 EX DC
* Sigma 18-50mm F/2.8 EX DC Macro
* Tamron SP AF17-50mm F/2.8 XR LD - i know works

Wide angle lenses never are meant to work with a tc. It may physically work (but the 10-20 is too slow anyway for AF at the longer end), but results are disappointing. You will combine the weak spots of the wide angle lenses (distortion, vignetting, loss of corner IQ) with the weak spots of the tc (additional loss of corner IQ, sometimes additional distortion).

No lens manufacturer ever recommended to use a tc with a wide angle lens.

Also, tcs should only used with zoom lenses, if recommended for certain modells (like the dedicated tcs for the old Vivitar Series 1 70-210 zooms or the current Sigma Apo tcs etc.), otherwise image quality is completely hit and miss.

* Tamron AF70-300mm F/4-5.6 Di LD Macro 1:2 - i know works

It works physically, but you get an extremely slow combination, which you want to step down another two f-stops for optimum performance. That is hard to use.

* Pentax SMCP-FA 50mm F/1.4
* Sigma 105mm EX DG F/2.8 Macro

These would be the only lenses, I would personally consider to use with a tc, though it doesn't make much sense. Combine the 50mm with the tc and you are very near to the 105mm Sigma without the tc.

The Sigma Macro might benefit from the tc, because a longer focal length macro lens is sometimes a very useful tool.

My remarks are very general and based on my experience with different tcs - not the Promaster. So, it is up to yourself, whether the Promaster, combined with any of your lenses delivers the sharpness and contrast you require.

Ben

01-19-2009, 07:58 AM   #5
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Thanks Ben for the insight
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