Is the 2X converter compatible (autofocus) with 70-200F4L?

[vasanthd]

Hey all Digi Photographers,
I have a Canon 20D with 70-200 F4L and loving every momemt with it. I am a aviation enthu and would like to extend my possibilites with my current lens. I am planning to buy the 2X teleconverter either Canon or Sigma. My only question is will the autofocus work when stacked with the 2X along with my 70-200F4L lens? Also one another question would be; which brand to choose? I am not pretty picky on the price, but saving $100 on the sigma would help me invest on a very nice bag!

Please do advice.

Thanks in advance.
Regards,
Vasanth

[TheObiJuan]

You will have to go with Tamron or Kenko, since the lens would be at f/8 all the time, the 20D wont focus with the canon or sig.
I use the tamron tc and I think it's great! (cheap too)

[vasanthd]

Istnt my lens at F4 all the time?

-_- Vasanth

[TheObiJuan]

Not when you tack on a teleconverter. If you use a 1.4x then you get f/5.6, with a 2x, you loose a lot of light and it becomes an f/8 lens. It will still autofocus with the tamron or kenko converters though, with canon or sigma, it won't.

[Rhys]

If it's aerial displays then put the lens on infinity and on manual focus. I'm pretty sure most things will be sharp.

[vasanthd]

Hi Juan,
Thanks for your reply. I have a question yet may sound silly. You say that the lens aperature will come down to F8. So the focusing problem starts only when suitable light does not go into the camera at F8 (which is a smaller hole when compared to F4..correct?). But most of my pictures, I take it at F11 like this - http://www.airliners.net/open.file/863617/L/ which would mean lots of light and to get more sharper pictures. So effectively if I opt for the extender, I am going to set myself to F11 or nearer to get this sharpness. So here is my question. Will my camera autofocus now in this bright day light when set manually to F11?

To Rhys: I usually take pictures when planes are still in gear and while taxing past me. So mostly it wont be infinite focus distance.

Thanks.
Regards,
Vasanth

[TheObiJuan]

The canon and sigma teleconverters have metal contacts that do not allow for autofocus to be had with a 2x on a f/4 lens, or 1.4x on a f/5.6 lens, like the canon 400 f/5.7.

The tamron does allow it.My sigma 70-300 APO Macro is an f/4-5.6 and I use my 1.4 on the telephoto end without problems. It is a little slow to focus sometimes, but that's what manual focus is for. :p

So once again, if you wish to use a 2x sigma or canon teleconverter on your f/4 lens, you will not ever be able to autofocus.

The 70-200 is pretty sharp at f/4 and very sharp f/5.6 and f/8, on a 20D going to f/11 or smaller for more sharpness is hopeless. At f/16 it won't get any sharper, but your depth of field will increase.

[Rhys]

To Rhys: I usually take pictures when planes are still in gear and while taxing past me. So mostly it wont be infinite focus distance.

Thanks.
Regards,
Vasanth

Ah. Not like my airshow pictures. I took those with a 500mm f8 Sigma mirror lens with 3M 640 ASA slide film while standing on the control tower roof in slight drizzle.

[vasanthd]

hi all,
tnx for your valuable replies ... yet i have one more clarification - http://www.bhphotovideo.com/FrameWork/charts/canon2xExtender.html ..here the compatibility says possible with a * onto it. so does it mean the AF works flawlessly only with the EOS-1v and EOS-3?

Thanks.
Regards,
Vasanth

[cwphoto]

hi all,
tnx for your valuable replies ... yet i have one more clarification - http://www.bhphotovideo.com/FrameWork/charts/canon2xExtender.html ..here the compatibility says possible with a * onto it. so does it mean the AF works flawlessly only with the EOS-1v and EOS-3?

Thanks.
Regards,
Vasanth

Also, EOS-1D series as well. And I wouldn't say it works flawlessly, AF slows down a fair bit with the 2x.

[TenD]

You may shoot with your lens stopped down, but when it focuses and when you are viewing the image through the viewfinder, the lens is wide open. Canon cameras have some trouble with AF on lenses with a max aperture of more less than 5.6. Obijuan is right about the contacts too, there is a way you can tape the contacts to allow the AF to work on slower lenses, but in this situation the AF is usually slow and inconsistent.

[TheObiJuan]

You may shoot with your lens stopped down, but when it focuses and when you are viewing the image through the viewfinder, the lens is wide open. Canon cameras have some trouble with AF on lenses with a max aperture of more less than 5.6. Obijuan is right about the contacts too, there is a way you can tape the contacts to allow the AF to work on slower lenses, but in this situation the AF is usually slow and inconsistent.

that is the case with my 70-300 at the tele end. I just manually focus. If the lens had HSM, I could get it to autofocus A LOT faster.

Sadly, the 135L with a 1.4TC also acts up, and it is a f/2.8 lens with the tc! :mad:
I have only tested it in low low light, so I will see how it acts in normal-bright light.

[24Peter]

FWIW - I'm using the Tamron 1.4XTC with both my Canon 28-135IS 3.5-5.6 and Canon 75-300 IS USM. Auto focus works fine with both - indistingiushable from w/out the TC. However, it's the cheaper Tamron TC - not the one recommended for L glass. My brief experience of owning the Canon 70-200 F4L was that AF was hit or miss with a Canon 2XTC and only worked in the lower end of the zoom range.

[cwphoto]

My brief experience of owning the Canon 70-200 F4L was that AF was hit or miss with a Canon 2XTC and only worked in the lower end of the zoom range.

AF shouldn't work at all with this combo unless mounted on a late 1-series body.