My wife has a Canon EF 100-400 f4.5-5.6L IS USM Telephoto Zoom Lens. Price is not that important to me, but I am unsure which of the four extenders I should purchase.

Canon has four extenders that I have found:

  • 1.4x EF MIII
  • 1.4x EF MkII
  • 2x EF MkIII
  • 2x EF MkII

Logic would state that the 2x units should give the benefit of much further distances to be accessible, however the 2x units seem to get a much worse press than the 1.4x. Again logic states that the Mk IIIs should be better than the Mk IIs but again I am left confused by the reviews I have found.

It appears that with most of these lenses autofocus may be lost, we tried a non expensive lens from the store(£80) which had the same problem, however the image on the camera appeared good. I am a complete amateur.

  • \$\begingroup\$ The part about using 2x over 1.4x converters is already covered in this question/answer: Are there any downsides in using 2x extenders?. I would suggest removing that from this question and instead just asking about MkII vs MkIII versions of the extenders. \$\endgroup\$
    – dpollitt
    Sep 24, 2012 at 19:35
  • \$\begingroup\$ I would like to leave the question as it is, as I presume there may also be problems with the 1.4x as well as the 2x and the original question may answer this as the suggested one does not.if thats ok dpollitt? \$\endgroup\$
    – Dennis
    Sep 24, 2012 at 21:15

2 Answers 2


Simple answer: DO NOT USE A TC ON THAT LENS!!!

I own that lens myself, and I have tried to use it with several TC's, including Canon's Mark III 1.4x and 2x TC's, as well as a Kenko 1.4x PRO 300 DGX TC. Neither of the Canon ones work...even the 1.4x...due to the lack of f/8 AF on anything but Canon's 1D series bodies (1D X excluded). The Kenko 1.4x TC allows me to AF with the 100-400, but ONLY in extremely awesome light. Even in awesome light, AF is very slow, and does not necessarily "lock" when the image is perfectly focused...sometimes it front or back focuses ever so slightly (which is probably more due to the Kenko TC's logic than anything else.)

That lens really is NOT designed to work with a TC, and you are just wasting money if you think you'll be able to. The AF won't be usable in the vast majority of circumstances, and in the few cases where it is barely usable, it still won't "really" be usable. You might be able to get away with 1.4x teleconversion, but 2x teleconversion is definitely out of the question (no camera on the planet will AF usefully at f/11 unless you have pure, unadulterated, and impeccably brilliant Heavenly Light of God illuminating your subject...just far too little light otherwise.)

Teleconverters are generally designed for use on lenses of superior quality and wider maximum apertures. Any lens with an f/4 aperture will work with a 1.4x TC, and any lens with an f/2.8 aperture will work with either the 1.4x or 2x TC's. In general, Canon TC's were really designed to work with Canon telephoto lenses, namely the following (lenses can be of any generation, however the most recent lenses, the Mark II IS versions, provide incredible results even with 2x TC's that outpace the IQ even from a bare 100-400mm L lens):

  • Canon EF 70-200 f/4 L
  • Canon EF 70-200 f/2.8 L
  • Canon EF 135mm f/2 L
  • Canon EF 200mm f/2 L
  • Canon EF 300mm f/2.8 L
  • Canon EF 300mm f/4
  • Canon EF 400mm f/2.8 L
  • Canon EF 400mm f/4 DO
  • Canon EF 500mm f/4 L
  • Canon EF 600mm f/4 L
  • Canon EF 800mm f/5.6 L (1.4x only, if AF on 1D body desired)

In Canon EOS 1D bodies, which offer center-point f/8 AF, all of the lenses above may be used with both 1.4x and 2x TC's. In situations where manual focus will be used, such as moon photography, the 1.4x and 2x TC's may be stacked, producing even longer focal lengths (in the case of the 800mm lens, one could convert it to a 2240mm f/16 lens!)

I have recently used the Canon EF 300mm f/2.8 L II IS lens on my Canon 7D body. The results, with both my Kenko 1.4x PRO 300 DGX and the Canon EF 2x TC III are unbelievable. The Canon EF 300mm + EF 2x TC III combination, which is a 600mm f/5.6 lens, produces results that are far superior to my bare EF 100-400mm f/4.5-5.6 L lens any time, in any light. Details are sharper and clearer, even in the corner of the frame, with the 2x TC, than I thought possible. So when you hear anecdotes like "The 2x TC will degrade IQ worse than if you just upscale your image 2x", stop listening. The Mark III versions of Canon's TC's have unduly inherited some of the bad rap their Mark II predecessors garnered. In all honesty, a lot of the bad rap the Mark II TC's receive today is not really warranted, as they were created during a much earlier era of digital photography, during a time when film was still considered superior or just as good as digital alternatives (which really wasn't that long ago in normal terms.) Digital camera technology has moved incredibly fast, and simply outpaced the optical capabilities of previous teleconverters, requiring replacements.

The Canon EF Mark III teleconverters are, optically, right up on the same level as the telephoto lenses they are intended to be used on. They use the same high quality glass, antireflection coating, build durability and weather sealing as Canon's most expensive $14,000 lenses. They exhibit considerably less distortion than the Mark II counterparts.

The only real caveat is that they really weren't intended to be used on the EF 100-400mm lens. If you attach any one of those four TC's to the 100-400 and an EOS body that does not support f/8 AF, the built-in logic chips in all three devices will prevent any kind of AF at all.

  • \$\begingroup\$ Once again Jrista some excellent, considered advice, off to work now, I will study your answer in great detail on my return. Thanks again. \$\endgroup\$
    – Dennis
    Sep 25, 2012 at 7:50
  • \$\begingroup\$ Wait a second, how does comparing the 300 f2.8 + 2x mkIII to a bare 100-400 f5.6 L indicate how much better the 2x mkIII is vs the 2x mkII? The 100-400 has (as I've said many times) terrible image quality while the 300L f2.8 is one of the sharpest lenses Canon produces up there with the 135L and 200 f2L. A:B testing indicates that there isn't any considerable difference in PQ between them (kennewcombe.com/Teletest2.html) which means you could still be better off just doubling the resolution in post. \$\endgroup\$
    – Shizam
    Sep 25, 2012 at 16:50
  • \$\begingroup\$ @Shizam: The Mark II versions of both EF TC's have poor IQ at the edge, and VERY poor IQ in the corners. The IQ falloff from the center is pretty extreme. Thanks to the Mark III's reduction of distortion (considerably), edge and corner sharpness is far better, and its use of UD elements to reduce CA. CA in the Mark II's is quite pronounced...I've never seen any with the Mark III's. The Mark III's have better MTF's as well, resolving more detail than the Mark II's. \$\endgroup\$
    – jrista
    Sep 25, 2012 at 17:12
  • \$\begingroup\$ As for the difference between a 1.4x and 2x TC, vs. upscaling a non-converted image, check the second set of photos on TDP's 1.4x TC review. The difference in IQ between the 2x, the 1.4x upscaled to 2x size, and unconverted upscaled to 1.4x and 2x size is HUGE. There is no question that the 2x TC produces far better IQ than an upscaled image, either from a bare lens or even a lens with the 1.4x TC attached (although the difference with the 1.4x is less). BTW...your link, doesn't compare IQ when wide open. :\ \$\endgroup\$
    – jrista
    Sep 25, 2012 at 17:14
  • \$\begingroup\$ As for the 100-400mm lens, it doesn't produce "terrible" IQ. It does not resolve the same kind of detail as a $6000-$14000 Canon supertelephoto, but it is far, far from a "terrible" lens. It takes some skill to extract the most IQ you can from it, even wide open. A great example of the IQ you can extract from a 100-400 is Daniel Cadieux's Bird Photography. He produces photos from the 100-400 that rival photos taken by seasoned professionals using $10k (or more) lenses. The only meaningful difference is no real TC support on the 100-400. \$\endgroup\$
    – jrista
    Sep 25, 2012 at 17:20

Depending on what camera you're using you will lose auto focus because some bodies only AF up to f5.6 and some only AF up to f8, attaching the 1.4x to the 100-400 tells the body its now a ~f8 lens and attaching the 2x tells the body its a f11 lens. You can get around this by putting a bit of tape over the adapter that transmits that information or by using a non-canon adapter.

To address the other question '2x vs 1.4x', the 2x very noticeably degrades image quality (among other issues) while the 1.4x doesn't impact image quality as bad. Some would say the 2x degrades quality worse than if you just increased the resolution of the photo 2x in post-processing where the 1.4x actually fares better than if you did 1.4x magnification in post.

  • 1
    \$\begingroup\$ Note, you can "get around it" by using tape, but that doesn't mean that it will actually autofocus, that just means you can let the camera attempt to autofocus! Also, neat note about increasing resolution in post, never heard it put that way. \$\endgroup\$
    – dpollitt
    Sep 24, 2012 at 20:32
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    \$\begingroup\$ When I was looking at the comparison shots of adding the 2x mkIII to the 70-200 2.8 mkII I was amazed at how good the images were compared to without. It seems the mkIII are really a big improvement over the mkII, but whether this would apply in the same way to the 100-400 L I've no idea \$\endgroup\$
    – Dreamager
    Sep 24, 2012 at 21:31
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    \$\begingroup\$ The 100-400 will most definitely not AF at f/11, no question about it (I've tried, and failed, many times.) The best way to get the 100-400 to AF at f/8 is with the Kenko 1.4x Pro 300 DGX teleconverter, which reports a max aperture of f/5.6 to the camera (although EXIF still comes out correct, showing f/8). You need some REALLY FREAKING GOOD light to actually successfully AF with the 100-400 at f/8...such as midday sunlight with good contrast. Outside of that, f/8 AF is a bust with the 100-400 as well in a general sense (and excessively slow, so not really useful outside of still subjects.) \$\endgroup\$
    – jrista
    Sep 25, 2012 at 3:58
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    \$\begingroup\$ Regarding the comment about the 2x TC degrading IQ. That is far more true about the EF 2x TC II, however hardly true about the EF 2x TC III. I recently used the Canon EF 300mm f/2.8 L II and EF 2x TC III myself to take thousands of photos of birds. With the 2x TC III attached, the 600mm combo produced far better images of vastly superior IQ to my bare 100-400mm f/4.5-5.6 L IS lens. The 2x TC III gets blamed for a lot of the shortcomings of its predecessor that it most certainly does not deserve. The problem is not the TC...in this case, the problem is the 100-400mm lens. \$\endgroup\$
    – jrista
    Sep 25, 2012 at 4:01

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