Need A Definitive Answer HELP!

TheDanishDanger

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Will a Canon 70D with a 400mm F5.6 AND a Canon 1.4 iii extender autofocus at smaller apertures or even at all? I've researched and get conflicting opinions.

Really want to use this setup for BIF.
 

DB_Cro

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Small aperture = big F number, your 5.6 would be a F/8 with the converted, it should focus fine.
I thought the issues were focusing at BIG apertures with converters, no?
 

tirediron

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F8 is generally about the limit of where most modern AF systems, especially consumer-grade systems start to falter, but it should work, at least out of doors.
 

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I've researched and get conflicting opinions.
Make sure the extender has electrical connections for your Canon camera and lens, and has at least the claim that it will operate the lens.
 

DB_Cro

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Newer should always work, it's freaking Canon, we'd all know if it didn't, I figure.
 
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TheDanishDanger

TheDanishDanger

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Thank for the help guys, I just read that the main issue is the camera body that doesn't allow it. I read that only 1D models will allow the autofocus for this combination to work. That's my concern.
 

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That sounds very strange to me, 70D and especially 7D mark2 (which are very similar) are a very common choice for sports and I'd expect
it work, wouldn't even consider to investigate it! :-/ Then again, how often do you need more then a 640mm (35mm eq on the crop body) lens!? o_O

Damn. :)
Sometimes cropping works better then an extender. o_O
 

Overread

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Actually the answer is yes and no.

If you are shooting normally with the viewfinder then once you go smaller than f5.6 as teh detected maximum aperture for a lens (or lens+teleconverter combo) then the AF won't engage.

If you are shooting with live-view though the limit shifts to f8; though the live-view AF is a different setup so it might or might not be as reliable/fast.


Note you can "tape the pins" on a teleconverter so that the camera doesn't see it attached; the AF will thus engage, but as mentioned above, its speed and reliability will become less and you'll want good light to work with. The reason partly for the limit is that the mirror assembly sends light up into the viewfinder, but also reflects a portion down into the AF sensors; so the sensors only get a part of the light to work with, not all of it. The live-view though gets all of the light (as there's no need to reflect the light anywhere else) which is why it has a greater range of limits to work with.
 
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TheDanishDanger

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Actually the answer is yes and no.

If you are shooting normally with the viewfinder then once you go smaller than f5.6 as teh detected maximum aperture for a lens (or lens+teleconverter combo) then the AF won't engage.

If you are shooting with live-view though the limit shifts to f8; though the live-view AF is a different setup so it might or might not be as reliable/fast.


Note you can "tape the pins" on a teleconverter so that the camera doesn't see it attached; the AF will thus engage, but as mentioned above, its speed and reliability will become less and you'll want good light to work with. The reason partly for the limit is that the mirror assembly sends light up into the viewfinder, but also reflects a portion down into the AF sensors; so the sensors only get a part of the light to work with, not all of it. The live-view though gets all of the light (as there's no need to reflect the light anywhere else) which is why it has a greater range of limits to work with.

Okay so just to make sure we're on the same page, I can still shoot normally, say around f9 with the 400mm and tele and autofocus should engage.
 

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You can shoot around f8 and the auto-focus will NOT engage if you are using the viewfinder.
You can shoot around f8 and the auto-focus will engage if you are using live view.


That is unless you "tape the pins" (google it I can't recall which pins to tape over) which will trick the camera into not seeing the teleconverter attached; as such the light is the same, but the camera will only see the lens and thus will engage auto-focus in viewfinder mode. Speed and reliability will, however, be affected.
 

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