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01-12-2014, 08:05 PM   #1
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vivitar 2x converter

I have a Vivitar Series 1 2XMC4 AF converter, on a Sigma DC 18-200mm 1:3.5-6.3 lens, using a Pentax K10D camera.
The lens keeps searching to find a focus and will not take the pictures????? What is wrong, setting on the camera,
converter, or what??? It does the same with my Tramron 70-300mm lens. Thanks for your replay. Bob

01-12-2014, 08:21 PM   #2
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QuoteOriginally posted by rca1 Quote
I have a Vivitar Series 1 2XMC4 AF converter, on a Sigma DC 18-200mm 1:3.5-6.3 lens, using a Pentax K10D camera.
The lens keeps searching to find a focus and will not take the pictures????? What is wrong, setting on the camera,
converter, or what??? It does the same with my Tramron 70-300mm lens. Thanks for your replay. Bob
Too dark to focus due to light loss through the converter? Your lenses don't seem to have large max aperture...I'm not sure, better wait for better answers.
01-12-2014, 08:22 PM   #3
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While you are waiting please try auto focus again in a brighter place if you haven't done so ;-)
01-12-2014, 08:28 PM   #4
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See if it works at 18mm that should be the brightest point for that lens. At 200mm you are already at f/6.3, add the 2 stops you lose with the TC and you are f/13. Far too dark for reliable auto focus. Even at 18mm the effective aperture will be f/7.1 which is marginal for auto focus.

As suggested above, try it again in very bright light, if it works there then you have isolated the problem, if it does not work in very bright light at 18mm then maybe there is a problem with the TC.

Is the Sigma 18-200 a screw drive or HSM version? I don't believe that TC will work with HSM or SDM.

01-12-2014, 08:59 PM   #5
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2x converters in general, particularly the 4-element variety, usually don't perform that well. Consider as an alternative just using your lens at 200mm and cropping. I never had much luck starting with a consumer-grade telephoto zoom and adding a converter to that.

I used to have a 7-element 2x vivitar for my canon lenses, and it was useful for macro applications (not flat-field by any means, but useful for non-flat subjects.) But I used it mostly with an f1.4 lens.

I might consider trying a 1.4x converter on my f2.8 50mm "close focus" lens to get a little more subject distance and magnification for macro applications, since the large-ish filter size somewhat limits the use of most multi-element close-up attachments.
01-12-2014, 09:03 PM   #6
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2x converters in general, particularly the 4-element variety, usually don't perform that well. Consider as an alternative just using your lens at 200mm and cropping. For a similar price as a converter you could probably get an inexpensive used 300mm (or zoom with 300mm at the long end) that would probably top out at about f5.6. I never had much luck starting with a consumer-grade telephoto zoom and adding a converter to that. And assuming you're using the 6.3 end, I can't image you can see much through the viewfinder, much less use autofocus.

I used to have a 7-element 2x vivitar for my canon lenses, and it was useful for macro applications (not flat-field by any means, but useful for non-flat subjects.) But I used it mostly with an f1.4 lens, so I could see to focus.
01-13-2014, 04:48 AM   #7
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Virtually all AF cameras require a native aperture of F6.9 or faster to AF reliably. A 2x teleconverters takes away 2 full stops so the 18-200 becomes an. F7-12.6 and the 70-300 becomes something like an F9-11 lens

There is no way for the AF to function
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