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Old Feb 8, 2008, 4:48 AM   #1
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Hello,



I was wondering if I should get the canon extender for my 70-300 Canin lens with IS?

Does the auto focus still function? If not what would the best choice be instead of the Canon extender?

Thanks.


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Old Feb 8, 2008, 5:31 AM   #2
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The simple answer is no, it won't AF. Well assuming you are talking about a 1.4x tc then at 70mm when the aperture is f4 this will become f5.6, the smallest aperture that you can AF on anything apart from a 1 series camera. As soon as you zoom past that then AF will be lost as the aperture will get smaller still.

Honestly I would not put a TC with this lens unless you are very good at manual focusing (so if you have a 40D with Live View when you might be able to then you might get away with it).

The lowest price lens in this range(off the top of my head) that works well with a TC is the Sigma 100-300mm f4. As it is f4 then you can't use a 2x TC on it as again this takes it to f8 which is took small an aperture to focus. With a f2.8 lens then you can get away with a 2x TC although results vary, basically adding a TC will reduce the quality of the information getting through to the camera as it is going through so many pieces of glass.
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Old Mar 4, 2008, 5:46 PM   #3
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Thanks, Mark!

It looks like I will save some money.


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Old Mar 4, 2008, 6:10 PM   #4
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Not a problem.
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Old Mar 4, 2008, 10:57 PM   #5
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Canon extenders only work on the "L" class lenses, don't know about after market extender if they will work or not.




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Old Mar 5, 2008, 8:01 AM   #6
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Mark I was told this tele will work with auto-focus:

Kenko 1.4x Pro 300 DG converter.
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Old Mar 5, 2008, 8:13 AM   #7
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Sorry to say apart from the EOS 3 SLR and and the 1D series which will AF at f8 you will not get full AF with a 1.4x TC on this lens. It should AF at 70mm when the aperture is f4 (f5.6 with TC), but as you zoom you go over f5.6 so the AF will not work.
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Old Mar 5, 2008, 9:17 AM   #8
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Mark1616 wrote:
Quote:
Sorry to say apart from the EOS 3 SLR and and the 1D series which will AF at f8 you will not get full AF with a 1.4x TC on this lens. It should AF at 70mm when the aperture is f4 (f5.6 with TC), but as you zoom you go over f5.6 so the AF will not work.
Ahh got it, Thanks for the info. The photos I have seen with this must have been using manual focus.
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Old Mar 5, 2008, 3:36 PM   #9
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Mark1616

The Kenko TC does not transmit the aperture info therefore any camera will AF with the EF 70-300 IS pass f/5.6 in good light... In bad light the AF would hunt (which is what Canon is trying to prevent). On a Nikon camera there's no f/5.6 firmware block and their camera will try to AF with any aperture (although not recommended)

-> This TC has the same effect as taping the two last pins on the camera which block the aperture info from being transmitted
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Old Mar 5, 2008, 4:36 PM   #10
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Very good point I had completely forgotten that effect as I have previously used one!

Thanks for stepping in
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