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05-13-2011, 01:18 PM   #1
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Advice in choosing Vivitar 2Xmc4 AF teleconverter

Hi you all!

I'm considering of buying the Vivitar 2xmc4 AF teleconverter, the budget is about 100$.
I'm using a k-7 with the Kit lens (DA 18-55) & also a Tamron 70-300 Di-Ld.
After wondering around and doing quite a research regarding that teleconverter, i still haven't got a clue whether it will work with both of my lenses (especially with the 70-300) or fit the K-7.
Does anyone have an answer on that?
If so, will the AF will be functional?
Is it a good choice for me, considering that price?
Tanks for the help,

Dror

05-13-2011, 02:08 PM   #2
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aside from the degraded image quality, although the TC supports AF (not sure about HSM but definitely screw drive) the lenses you plan to use it with are so slow,,that you will probably have difficulty with achieving AF lock.

for AF to function reliably, you really need lens plus TC to be below F6.7

With a 2x TC that really means a lens at F3.5 or faster F2,8 being preferred.
05-14-2011, 02:53 AM   #3
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I see...thanks for the quick reply.
But assuming i'm using a MF and i do not going to buy a new lens with low f now, is it still worth buying if i want to have a greater focal length?
Has anyone got the experience with such TC and this kind of lens?
05-14-2011, 05:25 AM   #4
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I don't know the tamron well enough to advise

Many AF zooms have a short focus throw which makes accurate manual focus difficult. Add to that a dark viewfinder and I would think it could be frustrating. Many would suggest cropping in would give better results

05-14-2011, 07:15 AM   #5
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MF with Tamron 70-300 + 2x TC will be very hard if not impossible.
The focusing throw of that lens is very short and combined f stop at 300 mm will b f11. That will be one very dark VF even with K-7!
I mean, it's doable but I don't suppose you'll get many keepers. Add another factors, the Tamron is not at it's best @ 300/5.6. Even one stop down will make it 300/8 add 2x TC and effective will be 600/16. You'll need very sunny day to get anything even slightly moving sharp, forget handholding, and you'll need rather sturdy tripod. Add MF and rather medicore quality (4 element 2x TC are not the greatest + underwhelming performance of the lens at 300mm) and I don't think it's worth even going through the hassle of trying it out.
05-14-2011, 09:38 AM   #6
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OK, you've got me convinced.
I guess i would wait until i'll have enough money to buy me some zoom lens with f2/8.
Thanks very much for all the info.
05-14-2011, 03:14 PM   #7
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QuoteOriginally posted by DROREN Quote
OK, you've got me convinced.
I guess i would wait until i'll have enough money to buy me some zoom lens with f2/8.
Thanks very much for all the info.
Hmmm, didn't take much to convince you of the futility of this setup, but I like trying futile things. Just some quick shots made after reading this thread: These were shot with a K20D + KatzEye split prism finder, Tamron 70-300 @300mm, manually focused. A Tokina EL 2X TC I bought recently to convert it into a PK/A extension tube (probably about the same optical quality as the Vivitar you were looking at), mounted on a monopod. Nothing to write home about but I think still acceptable. The short focus throw makes focusing a chore but doable. I go by the adage; it's better to get something rather than nothing. I suppose one would double the aperture value in the exif to arrive at the true aperture value.

Thanks,

Last edited by excanonfd; 06-15-2011 at 09:00 PM.
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