extenders 1.4x

[yeoness]

Hello all.

I purvhased a 1.4x teleconverter to go on my 100-400l usm lens. Unfortunately i have lost Autofocus.:cry: On my other lenses if i manual focus my 20D bleeps and tells me when focus is achieved. Should this be the same using my T-con on my 100-400??

Thanks
yeonessl

[Freff]

Hi yeoness and welcome to POTN. I can't help with this one , but I would also be interested in the answer as I have a 1.4x on the way.

[GeneMan88]

Did you buy a Canon 1.4X tele-con or another make?

edit: You also lose an f-stop with a t-con so the EF 100-400 becomes like an f/5.6-8, this could be the cause of your autofocus issues with the t-con/EF100-400 lens combo.

[Joseph Hoetzl]

Keep in mind, that with a f4 constant aparature, your max with the 1.4x will be f5.6 which will allow the autofocus to work fine, this becomes a problem when you are using a variable aparature lens such as the Canon 100-400 f4-5.6L.

When you reach a focal length where the aparature becomes above f4 with the TC you will loose autofocus capability.

[Wilt]

Keep in mind, that with a f4 constant aparature, your max with the 1.4x will be f5.6 which will allow the autofocus to work fine, this becomes a problem when you are using a variable aparature lens such as the Canon 100-400 f4-5.6L. When you reach a focal length where the aparature becomes above f4 with the TC you will loose autofocus capability.

Also, the minimum f/stop needed to retain autofocus is dependent upon which model of camera! A 20D retains AF at f/5.6 but a 1DsII retains AF to f/8. So if you want to use 1.4x with 100-400, you can either a) buy a non-Canon teleconvertor since it won't tell the camera about the slowed lens aperture, or you can b) buy a Canon 1.4x but use it with a 1DsII ! <wink>

[ssim]

In order to attain autofocus with a Canon 1.4TC you have to be using a lens with a fstop of at least f4 or better (wider). As the 100-400 is not quite this, you would lose your autofocus. Of course you can always do it the old way and foucs manually. The 1.4 does achieve autofocus on the 1 series body using the 1`00-400.

[exerda]

You're losing a stop with the 1.4x TC, so your lens drops to a max aperture of f8 on the long end--and non-1-series Canon bodies cannot AF past f5.6 for the max aperture.

There is a solution... you can tape over some of the contacts on the TC (do a search), thus "fooling" the camera into thinking it can still AF. AF may be slow and may hunt, but in the right light, it will still work.

[CyberDyneSystems]

http://photography-on-the.net/forum/showthread.php?t=41922

[yeoness]

:rolleyes: im using the canon one Geneman88

[yeoness]

:D im using the canon 1.4x geneman88.

[yeoness]

still getting used to the site. Sorry for the duplicate! When i use my 24-70 L USM if iu manual focus and keep my finger halfway down i get a bleep when focus is acieved. This doesnt seem to happen with the 1.4SO when do i know i have achieved good focus?