Help: 100-400 and 2x won't focus

[birdbrain]

I just got an eos 10d and may have messed something up. When I attach a 2x extender to the 100-400 f4.5 IS lens, the lens will not focus beyond 20 feet. It was yesterday, but isn't today. I reset all functions, turned off IS, am using manual focus from P zone. Any ideas are appreciated.

[Morden]

I believe that adding the 2x extender reduces the maximum aperture of the attached lens by 2 stops. The autofocus will only work with an aperture of f5.6 or greater, but an f4.5 lens, with the 2x, will be (I think) an f6.7 lens.

I believe also that there is a 'trick' involving taping over certain electrical contacts on the lens mount to allow autofocus to function, but I do not have details of this. No doubt another regular poster here will respond regarding this.

[birdbrain]

Than you for your reply, but I can't even focus manually. Even using mode M !

[Jeppe]

Isn't there a focus-limiter on the 100-400 ?? Just beside the AF/MF and IS On/Off switches..

[birdbrain]

There is a range limiter. Either 1.8 to infinity or 6.5 to infinity. Changing this has no effect.

[mrchips]

Is the converter a Canon? I have never had a problem with my 2X II or 1.4 TC with the 100-400 outside of the horrible manual focus ring on the 100-400 not being sensitive enough.

[birdbrain]

Yes it is a Canon ef2x II. As I say, it was working and now it's not. So, I'm assuming I've done something wrong, just ca't figure out what. I mean what would stop the lens from focusing ?

[defordphoto]

Well, if you can't focus manually then I'd suspect the lens fousing mechanism is busted. Other lenses work okay?

[birdbrain]

Well I guess I'm not stating my problem very well. So allow me to try again.

With just the lens and my camera on or off, everything is fine. That is, even with the camera off I can focus just fine.

When I attach the 2x extender, I can focus out to about 20 feet and then it will not focus on anything further out. Even with the camera off.

I had no problem a few days ago, and I started reading the manual and setting this and that. Now I have this frustrating problem, and I don't have enough knowledge of the 10d to get myself out of it.

[chris maddock]

If you can't manually focus with the camera turned off, it ain't the camera.
Will the lens move the whole focus travel with the TC fitted but not the camera?

KRs
Chris

[birdbrain]

Yes, the lens is fine without the TC.

[chris maddock]

Weird, something must be interacting mechanically.

When you say it works fine without the TC, have you looked to see what travel the lens will make (on the distance scale, not looking through it) when it isn't mounted on the camera, both with and without the TC?

I can't think what could be fouling, the rear elements are deeply recessed even when at their furthest back, so I can't see that the TC would foul anywhere.

KRs,
Chris

[birdbrain]

My thanks to all who responded and my abject apologies. My problem was I can't tell the difference between an extension tube and a tele-extender.

[chris maddock]

Oooer!
Well, you caught us all out as well!
Glad all's OK.

KRs
Chris

[Jeppe]

O´boy.... LOL....

[Morden]

My thanks to all who responded and my abject apologies. My problem was I can't tell the difference between an extension tube and a tele-extender.
Ah, and there was no clue whatsoever in your nickname. :)

Never mind; no harm done!