Canon 2:1 extender problems

[audiman M6 AEN]

Help, can anybody tell me why my Canon 2:1 extender seems to be giving me problems.
I have a Canon 100-400mm 4.5-5.6 IS USM lens which works fine on its own on the Canon 50D, but will not focus when the extender is fitted with it. This lens and extender are two months old. Oh by the way it used to work.

If I put my other lens on, a Canon 70-200mm f2.8 IS USM on the 50D with the extender it works perfect

Thanks

Alan

[gary65]

Do you mean manually focus or autofocus ?

[Pete W]

The camera will not work in auto focus with the 100-400 due to the aperture size being f8/f9 with the 2x extender fitted.

[audiman M6 AEN]

Well it used to focus in autofocus but wont now. I tried to focus manually today and it still wont.

Thanks
Alan

[Pete W]

What won't the 100-400

[audiman M6 AEN]

Hi pete
Yes the 100-400, when you press the button on the camera the settings appear in the camera but the lens will not focus manually or auto withe converter on.
This is pointing up at the bright blue sky today at an aeroplane.

Alan

[Pete W]

Manual focus means setting to "MF" on the lens and then focussing by twisting the focus ring yourself, doing this has no effect ??

[baz]

I Alan
I have 100-400mm and x2 converter and as Pete said it will only work in manual focus switch the lens to mf and use the
focus ring.
Baz

[audiman M6 AEN]

Hi, Let me start again, when I bought the lens and the converter I fit them both on the camera and the autofocus worked fine. I took them off for storage and when I came to use them again they will not autofocus.
As you say turn the autofocus off to MF and I can manually focus.
Why will it not autofocus now? Canons literature seems to read that they will autofocus.
Thanks for your help it is appreciated

Alan

[Nog]

From the sounds of it theres nothing wrong with either your camera, the lens or extender.
Its a feature of Canon EOS that they do not autofocus above 5.6 with an extender. You may have initially had a poor contact with the lens which allowed the autofocus to work as described in this trick to get around the problem (taken from another site - hope this is ok):

The Canon Teleconverter Trick

Canon non professional dslr cameras such as the Eos 10d Eos 20d Eos 30d will cut-off auto focus when they detect a f5.6 lens in addition to a teleconverter.

It's quite simple to get around this by fooling the camera into thinking there is no teleconverter attached and continuing to auto focus by a simple trick.

Just place a thin strip of insulating tape over the three pins on the lefthand side (lens side of the extender). No damage will occur to the camera or teleconverter. Auto focus performance will not be quite as good as f5.6 but when you are using a lens such as a Sigma 500mm f4.5 with a 1.4x teleconverter, the amount of light reduction is minor and auto focus will still be very good.

[audiman M6 AEN]

Thank you all for the good information you have given me.
Hope you all have a good Christmas and a happy New year.

Alan

[LastPost]

Canon EOS cameras will only retain auto focus when used with a Canon Extender up to f/5.6 on all but 1 series EOS cameras.
A 1 series EOS Camera and a Canon Extender will retain auto focus up to f/8
The Canon Extender 1.4x adds 1 stop to the lens
The Canon Extender 2x adds 2 stops to the lens

Thus a Canon 50D with a Canon Extender 2x will only retain auto focus with a f/2.8 lens - because that becomes f/5.6
A Canon 50D with a Canon Extender 2x will NOT retain auto focus with a 100-400 because at 400mm the f/5.6 would becomes a f/11 lens and with a 1.4x becomes a f/8 lens