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Advice - Canon Teleconverters

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Advice - Canon Teleconverters

Postby adrhall » Mon Dec 10, 2012 6:39 pm

I have recently gladly invested in an EOS 5D Mark iii full frame, and for birds I often use an L series 100-400mm zoom lens with an EOS 7D.

Naturally with the 5D the effective focal length is reduced back to norm... is it possible to add a teleconverter to regain the effective focal length of the 7D - and still have the lens autofocus?

Canon seem to be giving me mixed answers to this question with each person i ask.

Any ideas anyone?

Thanks

Adrian
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Re: Advice - Canon Teleconverters

Postby laurence leong » Tue Dec 11, 2012 10:15 am

If I get it right, the 7D will give a crop factor of 1.5. If you use a 1.4 coverter you will get 1.4 times. My 1.4 Kenko converter is auto focus enabled
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Re: Advice - Canon Teleconverters

Postby adrhall » Tue Dec 11, 2012 9:52 pm

Lawrence

i think that each lens may or may not react well to teleconverters.... it seems a 70-200mm L 2.8 lens can handle autofocus whilst a 100-400mm L lens often cannot... ???

Some pamphlets of Canon's says it works - others that it doesn't. Do you have this lens?

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Re: Advice - Canon Teleconverters

Postby laurence leong » Wed Dec 12, 2012 9:05 am

No. I didn't.realise such problems exist.
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Re: Advice - Canon Teleconverters

Postby richardlbong » Mon Dec 31, 2012 7:40 pm

Hi Adrian, your 100-400mm lens has an effective f/stop of 4.5 - 5.6. At 100mm you will have a wide open f/stop of 4.5. Using the 1.4x TC, you lose 1 stop of light which technically gives you f5.6 amount of light and when you zoom you will be only getting an f8 amount of light at f5.6. Even if you use the original Canon 1.4x TC you can only use manual focusing. i don't think there are any Teleconvertors that can allow you to autofocus with this lens.
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