Stacking extenders

[forrest.berkshire]

Can you stack a 1.4x and a 2x extender onto a 200mm 2.8l IS lens? I guess that would be like an f8, so if

it is possible, would auto-focus still work?

[steve_dunn2]

<p>There's no such lens as a 200mm f/2.8L IS. If there were, then yes, it would be possible to stack a 1.4x and a 2x with it, but there are caveats. If these are Canon extenders, the 2x must be the II version; the original version of the Canon 2x can't stack with either version of the 1.4x (unless you put an extension tube between them, which increases magnification but sacrifices the ability to focus to infinity). Some third-party extenders will allow this sort of stacking.</p>

 

<p>Yes, this would be an f/8 lens. Autofocus will work on bodies which support autofocus at f/8. Bodies which don't support AF at f/8 may or may not work; they won't know it's an f/8 lens so AF will try to work, but it may be anywhere from somewhat reliable to completely useless, depending on the body, subject, and lighting.</p>

 

<p>Optically, this will be quit a bit less sharp than the lens is on its own. If you stop down a couple of stops, it might not be so bad, but then you're working with a 640mm f/16 lens, which is going to be a bit hard to use.</p>

[yves_jalbert]

I suspect you're referring to the 70-200 2.8 IS zoom. This one is compatible with both extenders and auto-focus will work with either one. As for both of them at the same time, hmmm, good question. Probably would work, but certainly not the best setup. I suggest you try it in the store before buying.

 

As a side note, if you use a 30D the 1.6 crop factor should give you about the equivalent of the 1.4x if you put the 70-200 on it (in terms of focal distance). I know it's not the same but you get the point. That would eliminate the light lost with the 1.4x and give you similar focal lenght.

[User_1172872]

"Autofocus will work on bodies which support autofocus at f/8." Perhaps. It isn't guaranteed. When you stack the extenders, the camera does not "see" the correct aperture. The aperture in the display will be 2X the maximum aperture of the lens. But it should be 2.8X with the stacked extenders. Even on a body designed to autofocus at f8, the speed of the motor will be too fast; the body has to "know" the correct aperture to slow down the autofocus motor. So you may have oscillation around the correct focus.

[jim_doty]

With the old version, you could stack the two teleconverters with a 12mm extension tube in between and use them on the 70-200 f/2.8 lens. It's been a long time since I did that, but it seems to me it wouldn't focus as far away as 50 feet. Autofocus with an EOS 3 was iffy, sharpness was nothing to write home about. It was a fun experiment.

 

Two original teleconverters plus a 12mm extension tube would focus to infinity with longer Canon glass. In BEYOND TO BASICS II (page 40), George Lepp shows a 2x mounted on the camera body, then the 12mm tube, then the 1.4x and then a 300mm f/2.8L lens (840mm total at f/8) and a pretty good looking photo that he took with the combo.

 

Jim

[bobatkins]

As above, you can with the MkII extender or the Mk I with a 12mm tube beteween them (though you'll probably lose infinity focus with most lenses other than the long telephoto primes). You may get AF if the body supports AF at f8.

 

However the bigger issue is whether it's worth it and I suspect the answer in your case may be no. I strongly suspect that a 1.4X + 2X on a lens like the 70-200/2.8 IS, or even the 200/2.8 won't give you very good results and indeed may be no better (or even worse) than cropping the image obtained using the 2x.

 

My experience of stacked extenders on lenses from the 600/4L to the 300/2.8L to the 300/4L has been unspectacular. Generally the results haven't been pleasing. It's basically a last ditch "nothing left to lose" strategy and typically the results using just a 2x have been better, even with a smaller subject size.

 

If you do try it I'd suggest stopping down the lens by at least one stop when you shoot. I know f11 is slow, but the results are likely to be sharper than at f8.

[John Crowe]

I used to stack converters and while it is fun and intriguing it really is not worth it. I have gotten much better results further cropping from one or the other. In the past couple of years I upgraded my lenses so much that I kept only one converter, a 1.4x. If I need more cropping then I do it in printing.

[paul_ho1]

I stacked a 1.4x II and a 2x II on my 70-200 IS L lens with a EOS 3. The camera incorrectly reported a f5.6 and auto focus was very slow and unreliable.

[forrest.berkshire]

Thanks all for the responses. I really just asked it out of curiosity. For the record, I am using

a 1D Mk II and it is a 20-200mm 2.8L.

 

Both of the extenders, I believe, are Type II's. So does that mean they won't stack? I also have

a 12mm Kenko extension tube that I could stick between them.

 

I don't know why I would ever need this set up, but it's nice to know just in case.

[will_webster]

You have all the equipment.

1s and 0s are cheap.

Why ask? Just try it.

[jeremy_gaston]

<p>I've done this with a 1.4x I and 2x II on a 70-200 I (non-is). Autofocus was a little shaky on 50D. On a 5D II, it was as snappy as if I had no extenders at all.<br>

On the 5D, it's a 198-560mm/f8, which is a pretty rangy lens for that distance. On the 50D (or any crop), it's a 313.6-896m/f8 equivalent, which has it's uses even if the autofocus is a little sketchy....<br>

For me, I was thinking the setup would be useful when shooting standoffs, etc. from block to a quarter mile away. Might not be quick enough for anything moving, and the lack of a "fine-tune" focus ring makes a difference...</p>