Should the AF Work?

[Charlie52]

I just purchased a 2X II extender. On one side of it I have a Canon 10D and on the other side I have a 500IS 4/L. I put it all together and the AF doesn't work. Is there something in the manual I'm missing or did I get a defective extender?

[Andy_T]

According to what I've read here on the forum, it will not autofocus because you lose 2 stops with the 2x extender so the camera can not aufotocus any longer (it won't focus over f/5.6).

With the 1.4 converter, you lose only one stop, so it's just below 5.6 and will work.

You might want to do a search for 'tape trick', though.

Best regards,
Andy

BTW: what are you shooting ???
500 x 2 x 1.6 crop factor accounts for a mere 1600 mm focal length (in 35 mm terms)

[Ian_H]

According to Canon's page about the 2x extender

The EF 2x II doubles the focal length of any lens it's mounted to, and reduces its effective aperture by two stops. With the EF 2x II, AF is possible with any EOS body if the lens has an f/2.8 or faster maximum aperture, and compatible Image Stabilization lenses maintain the IS feature when used with any current EOS camera.



Cheers
Ian

[CyberDyneSystems]

We need an Extender sticky..**EDIT**We NOW HAVE a T-con sticky!!! ** :) this is getting asked almost daily :)

Yes.. the 10D needs f/5.6 or larger to AF.

The f/4 lens times 2X = f/8 = no AF

FYI the f/4 lens times 1.4X = f/5.6 = YES AF

[Panza]

A bit off-topic but maybe we should create a FAQ on this forum. On it's own page like the image gallery. With a big link on top of the forum along with the "Usage FAQ" ?

That would help people a lot and save some topics a day.. :D

EDIT: Started a new thread regarding this:
http://photography-on-the.net/forum/showthread.php?t=41926