fabs
Carpal \'Tunnel
Reged: 10/04/2007
Posts: 2876
Loc: Beds/Bucks
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Bit of a long shot, but I have just ordered a Sony 70-200 f2.8 G lens and am considering purchasing the Sony 2x teleconverter.
I know it will reduce the maximum aperture to f5.6 but will it affect the actual performance of the lens? I have heard that teleconverters can cause issues with Autofocus but, as the teleconverter is specifically designed for this particular lens, I am hoping this will not be the case.
Has anyone here by any chance used this combination and, if so, any thoughts?
Cheers
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El Sid
Going potty
Reged: 14/04/2003
Posts: 9463
Loc: Sussex-by-the-Sea
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All teleconverters tend to reduce the absolute image quality to some degree but by and large OEM converters which are normally limited to use with the top end range of lenses minimise this about as much as is possible. Even with the Sony 2x converter your 70-200mm is unlikely to be quite as good as a 100-400m of similar optical quality would be let alone a 400mm prime. In print though unless you crop heavily or print very large it's unlikely that the difference is that significant.
Additionally the converter is rather lighter and cheaper than either an additional longer zoom or prime lens...
For a photographer who requires 400mm on a regular basis a dedicated lens is the probably the best option but for anyone who only needs 400m on the odd occasion a 200mm lens and 2x converter may well be more cost effective. I strongly suspect that the 70-200+2x combo will still give better image quality than many cheaper long zooms can manage.
AF issues usually only occur when the effective aperture of the pairing (actual aperture x converter strength) exceeds minimum usable aperture of the AF system. For instance on my Canons an f4 lens plus 2x converter gives an effective aperture of f8 but the maximum usable aperture for AF is f5.6. With a dedicated Canon converter the AF would be turned off - Canon converters report the real aperture to the camera and this disables the AF system. With a non-Canon converter the AF is not disabled but it does tend to become a little bit sluggish and tends to hunt a bit before locking on, for effective apertures beyond f8 it just hunts without ever locking on...
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Nigel
Completely BSRIPN 
ElSid Gallery
A camera in the hand is better than one in the cupboard........
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fabs
Carpal \'Tunnel
Reged: 10/04/2007
Posts: 2876
Loc: Beds/Bucks
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Thanks Nigel, that was very informative.
the reason I'm looking at one is that currently I use a Sigma 50-500 for Polo, which does an adequate job. My way of thinking is to use the 2x Teleconverter with the 70-200 in order to get better quality images (The extra 100mm wouldn't make that much difference). From reading your post, I'm thinking that this would be the way to go. In fact I could sell the Bigma, buy the Teleconverter and still have change! 
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RonM
Reged: 26/04/2001
Posts: 3722
Loc: Scotland
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Marc,
Nig has pretty well covered the subject but you should also remember that manufacturers design/optimise their tele-converters to work specifically with their 'top-end' pro lenses and to provide very good results from wide open in the case of the 70 - 200, f2.8 whereas with OEM converters you would have to stop down a stop or so to obtain comparable results.
The main benefits you will probably see with the 70 - 200 SSM and 2x converter is much faster and accurate AF and better Boké and hopefully better images all round
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Ron NRIPN
Everyone has a photographic memory, some don't have Film or Digital Memory.
Life is a Learning Opportunity
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fabs
Carpal \'Tunnel
Reged: 10/04/2007
Posts: 2876
Loc: Beds/Bucks
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Cheers Ron. The TC has just come down in price so it's even more tempting now!
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RonM
Reged: 26/04/2001
Posts: 3722
Loc: Scotland
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Marc,
Have you also considered the 1.4 TC? then you lose only a stop so the effective aperture is f/4, so with the crop factor of the sensor you you'll have a 420mm f/4 lens.
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Ron NRIPN
Everyone has a photographic memory, some don't have Film or Digital Memory.
Life is a Learning Opportunity
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fabs
Carpal \'Tunnel
Reged: 10/04/2007
Posts: 2876
Loc: Beds/Bucks
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Unfortunately I'm looking to use it for Polo, replacing the Sigma 50-500 so 200mm is a lot of focal length to lose.
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