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Autofocus problem using a 1.4x


canonfan46 5 1.1k United Kingdom
3 Mar 2013 5:08PM
Hi all,
I have a problem with a Canon 1.4x II extender so as usual I turn to the experts on Ephotozine.

I am using the following equipment:- Canon 7D, Canon 400mm f5.6 prime lens, Canon 70-200mm f2.8 L IS II, 1.4x extender.

I was out the other night photographing the moon using the 400mm prime with the 1.4x attached. Everything worked fine and I had some good images using autofocus with mirror lock-up enabled.

Today I had the same set up and was trying a bird shot. I disabled the mirror lock-up and when I tried the shot the autofocus would not come on. The back of the camera showed MF set.

I tried the 70-200 with the 1.4x attached and everything worked fine.

I repeatedly switched between the 400mm and the 70-200 but the autofocus would not work with the 400mm.
The autofocus also works normally when using the 400mm without the 1.4x.

Anyone any ideas on what the problem might be?

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rogerfry e2
9 525 United Kingdom
3 Mar 2013 5:18PM
The 7D wil only autofocus with apertures of 5.6 or less....by adding the convertor, you're effectively working with an f8 lens....so autofocus won't work.
canonfan46 5 1.1k United Kingdom
3 Mar 2013 5:23PM
that can't be right, I have used it many times with f11 and smaller
3 Mar 2013 5:35PM
Doesn't a lens do its focussing with the widest aperture available to it, then snaps down to f11 (or whatever..) when you actually press the shutter..?
canonfan46 5 1.1k United Kingdom
3 Mar 2013 5:39PM
I do know that the 400mm with a 1.4x attached has a maximum aperture of f8 and the camera does not allow the setting of anything larger than f8, but the autofocus should work with f8 and smaller.
arhb e2
7 2.5k 68 United Kingdom
3 Mar 2013 5:39PM
The 1D series are the only bodies that have usable AF with lens/tc set-ups above F5.6,
and the 400mm F5.6 will become F8 with the 1.4tc attached.

It is possible that your focus was set to infinity when you did your moon captures with the 7D - 400mm - 1.4tc,
making you think it was autofocusing?
rogerfry e2
9 525 United Kingdom
3 Mar 2013 5:39PM
It;s not a question of the aperture you're using....it's the maximum aperture of the lens which is the important thing. For the autofocus to work, the max aperture needs to be 5.6 or less.
canonfan46 5 1.1k United Kingdom
3 Mar 2013 5:41PM
Yes I agree, the lens has a maximum aperture of f5.6 and the converter makes it a max of f8, but the autofocus should work at f8
justin c 11 4.6k 36 England
3 Mar 2013 5:42PM

Quote:but the autofocus should work with f8 and smaller.


Not on a 7D it won't, it will only work up to f5.6. The Canon 1 series camera's will auto focus at f8.

You're better off focusing manually on the moon anyway. Just enable Live View and set the magnification to 5x or 10x.
rogerfry e2
9 525 United Kingdom
3 Mar 2013 5:43PM

Quote:Doesn't a lens do its focussing with the widest aperture available to it, then snaps down to f11 (or whatever..) when you actually press the shutter..?
.
That's correct.
lawbert 7 1.8k 15 England
3 Mar 2013 5:43PM
Im guessing with the mirror lock up you were in live view.

The 400 5.6 L will not take a canon convertor at all without taping pins on the lens to retain AF

The 70-200 2.8 is designed to work with any canon convertor whilst retaining AF.
canonfan46 5 1.1k United Kingdom
3 Mar 2013 5:47PM
If you look at the last post to my portfolio you will see a photo of the moon. As you can see on the metadata, it was shot with the 400mm + 1.4x at an aperture of f16 and with autofocus.

I have used this set up many times and always with autofocus
lawbert 7 1.8k 15 England
3 Mar 2013 5:56PM
It says manual exposure modeWink
canonfan46 5 1.1k United Kingdom
3 Mar 2013 5:57PM
manual exposure is not manual focusTongueWink
canonfan46 5 1.1k United Kingdom
3 Mar 2013 5:59PM
I have really poor eyesight close up and because of that I have never ever used manual focus, so I am now really puzzled by how I took that photo

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