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AF problems


I attached a Canon 500mm f 4.0 IS II lens to a Canon 1.4 III extender and attached this combination to a Canon -1D X.

Canon says this shouldn't be a problem. But there is a major autofocus problem. You need tp press the shutter again and again before it will focus. As soon as you move the focus point either further away or closer to the lens the autofocus doesn't work again. So it looks like the new 500 lens id not compatible with the 1.4 III extender.


There is no problem at all with my Canon 300mm f 2.8 IS lens.


has anyone noticed this problem too?





I wish I had the gear to do the test but since I don't I'll suggest what I've read countless times. Use the center AF point only with the big gun because you're now at f5.6 which explains why you're not having the same issue with the 300 + TC which ends up at f4.

"A skill is developed through constant practice with a passion to improve, not bought."

Thank you for your comments.


I only used the center AF point from the start.


Not sure if this was the cause in your case but you might want to check the menu AF:AF4 to see if the option "Lens Drive When AF impossible" is set to OFF or not. When set to OFF, if for some reasons the focus is out of range of the minimum focus distance (MFD)- either by your manually driving it or the AF driving it past...the AF stops working.  It will start working again only after you cycle the power.  This incredibly is per design.


I don't think it has to do with the extender per se...the extender will exacerbate the problem for sure since the MFD is changed for the worse.  Also, the 500mm lens plus extender belong in a different group as far as focusing is concerned versus your 300mm f/2.8...the AF for this combo is not as good which explains why you see it now and not before.


Even when the option above is set to ON, sometimes the AF does get confused and just sit there searching around a long time.  A quick power cycling and/or manual focus will solve the problem.  This happens to me from time to time (I use a 5DMk3 but it's the same thing) when I'm AI Servo tracking a bird in flight and it moves too close to me (closer than MFD) and stays there.  After that I usually have trouble focusing on anything doesn't happen all the time but it does happen.

Diverhank's photos on Flickr

Thank you for your help.


The option ' Lens Drive When AF Impossible' is set to OFF.


I tested the lens/extender/camera a little bit more today. The AF works well if I (auto)focus on subjects near my initial subject I focused on. 


If I move the center AF point much further away from or much closer to this subject the AF really struggles for some time. I need to press the shutter time and time again before it suddenly  will focus.

You might want to set the option to ON and try to see if it's better but I think that it is normal what you're seeing.

Diverhank's photos on Flickr

A massive, massive thank you from me!


Switching the AF4 setting: Lens drive when AF impossible to ON did work!

The camera/extender/lens combination works like a dream now. No AF problems at all. AF is very quick!


Canon hasn't been able to help me, but you did help me a lot.


Thank you again!!

You're welcome Smiley LOL . Glad it worked out for you.

Diverhank's photos on Flickr
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