Teleconvertor AF

[cloudhunter]

When you put a teleconvertor say 1.4x on a body and then put your lens on say 70-300 does the af still work?

I know canon 40d's with tc's dont according to google just wondering if that is a canon limitation or a tc limitation?

 

[Flash In The Pan]

Generally anything that gives you max aperture of less than f/5.6 when multiplied by the tc factor won't autofocus. If you put it on something that is already at a max of f/5.6 then the viewfinder will also be pretty dark. Sometimes you can get away with ramping the iso right up, but all you'll get are soft, noisy pictures...

 

[cowasaki]

When you put a teleconvertor say 1.4x on a body and then put your lens on say 70-300 does the af still work?

I know canon 40d's with tc's dont according to google just wondering if that is a canon limitation or a tc limitation?

Also if you attach a TC to a lot of lenses you risk damage to the TC and/or lens due to the lens inside sliding back (as part of the zoom mechanism) and smashing into the front lens of the TC. You need to check compatibility. The Nikon AFS 18-200 for example is NOT compatible with a TC. I know you're talking about a Canon but it might well be worth you looking at before you break something or waste any money. (someone that knows about Canons might now come back and say it does not apply to them )

 

[StewartR]

All the 70-300mm lenses on the market are f/5.6 at the long end, so they will generally not autofocus when used with a teleconverter. Some third-party teleconverters play tricks to disguise thair presence, fooling the camera into thinking the lens is still f/5.6 instead of f/8, and then the camera will try to autofocus; but at f/8 it will struggle.

Generally speaking only telephoto primes and pro-spec telephoto zooms can accept a teleconverter. Many other lenses can be phyically damaged if you try to fit a teleconverter. I'm not aware of any 70-300mm lens which is recommended for teleconverter use. Certainly you couldn't use a Canon teleconverter; you might be able to use a third-party one if it doesn't have a protruding front element, but be careful.

So to summarise:

(1) 70-300mm lenses are not designed for use with teleconverters and you'll have to hunt around to find one which can fit without damaging the lens.
(2) If you can find one which will fit, it probably won't autofocus.
(3) Image quality will take a big hit.

Still want to do it?

 

[HoppyUK]

Both of Canon's extenders have the protruding front element which prevents them from being fitted to a lot of lenses.

Kenko Pro 300 1.4x is the most highly rated alternative which does not protrude and fits a lot more lenses. I used one on a Canon 100mm macro quite happily, to give a bit more reach, but every lens is obviously different. You will lose AF at higher than f/5.6 though, and that rules it out as a practical alternative a lot of the time.