I'm using 5D MKII body and 100-400 f/4.5-5.6 lens. I want to use a 1.4 converter; will the Kenko converter work and autofocus properly?

4 Answers 4


I have used this combination before, and it really depends. Most of the Kenko 1.4 TCs will allow you to AF without any kind of tape tricks, however only when there is enough light. If you have particularly bright lighting conditions, then AF will work...albeit very slowly. In any other situation, AF will be spotty at best, if it works at all. In lower light situations, AF will usually just hunt back and forth, quite slowly, without ever actually locking on to anything.

You need to make sure you attempt focus on high contrast areas, preferably obvious contrast (not just microcontrast). If you try to focus with the Kenko+100-400 on an area that is largely uniform or similar in tone, then AF will usually just hunt.

I would also like to point out that, even assuming you DO manage to get AF working well enough to lock consistently, the 100-400 just doesn't have the base IQ necessary. Slapping on a TC will greatly exacerbate corner and midframe IQ issues, and the smaller maximum aperture immediately limits your diffraction-limited center-frame resolution.

Overall, it is really not a worthwhile option to use the Kenko 1.4x with the 100-400. It is really not a worthwhile option to use any TC with the 100-400...it just doesn't really perform well or produce keeper IQ. You are much better off saving your money for a better lens (i.e. 300mm f/2.8 can handily take a 2x TC III and still produce better IQ than the 100-400 on its very best day!)

If you need a larger subject in the frame...the best bet with the 100-400 is to figure out how to get closer. When it comes to wildlife and birds, some camo pants and shirt will go MUCH farther than a TC towards getting you more frame-filling shots, without any IQ loss (rather, with an IQ improvement, assuming your subjects don't flee.)

  • The TC will magnify flaws in the center portion of the lens, but the corner issues will be cropped out of the FoV, just like with a cropped sensor. The TC is taking the light circle projected by the lens and increasing the diameter of the circle by 1.4X. This has the same effect as reducing the linear measurements of the sensor by 1.4X. The optics of the TC will also add additional issues of their own.
    – Michael C
    Aug 7, 2013 at 23:28
  • @MichaelClark: Trust me...I speak from lots of personal experience (both using the Kenko on FF as well as APS-C). The Kenko has fairly rapid IQ falloff from the center. Even with the 600/4 II on my 7D, with the Kenko I get a fair bit of softening and some CA in the corners and some softening at the edges. The big improvement with the Mark III TCs from Canon was corner performance, and at least with the 1.4x, the difference between it and the Kenko 1.4x really shows (even on APS-C).
    – jrista
    Aug 8, 2013 at 0:12
  • Which means the defects are coming from the optics in the Kenko, not the original corner performance shortcomings of the 100-400 lens.
    – Michael C
    Aug 8, 2013 at 0:56
  • Please also note there are several grades of Kenko TCs. The 2X is offered in the 4 element MC-4, the 7 element MC-7, and the PRO 300. The 1.4X is offered in at least the MC-4 and Pro 300 versions.
    – Michael C
    Aug 8, 2013 at 1:04
  • The 100-400 definitely demonstrates softness in APS-C corners and a bit in the midframe. It is not a lot, but having shot with it for over two years, I am quite familiar with its optical characteristics. At f/7.1, that mostly clears up. Teleconverters both magnify the optical deficiencies of the attached lens, as well as having the potential to introduce their own. There is no question the Kenko adds some of its own, but it is not just 100% the Kenko doing so. It has a different curvature, which doesn't line up as well with the lens, hence the exacerbation of issues from both.
    – jrista
    Aug 9, 2013 at 0:34

jrista's answer sums it up rather well in terms of whether it is advisable or not to use any teleconverter/extender with the EF 100-400mm f/4-5.6 L IS. There is a lot of inaccurate information in several of the other answers and comments that should probably be cleared up.

My experience is primarily based on using a Kenko 2.0X Teleplus PRO 300 with a Canon EF 70-200mm f/2.8 L IS II mounted on a Canon 7D. I have tried other combinations of lenses and bodies just for the sake of experimentation. Here is what I have learned.

  • Most older Canon cameras rated to focus at f/5.6 or wider, unlike newer bodies that may be firmware limited to turn off AF above f/5.6, will still attempt to focus when an f/8 combination is mounted. Sometimes they even succeed. For example, an EF 24-105mm f/4 L IS + Kenko 2X PRO 300 + Canon 5DII will Auto Focus in bright conditions. The combination focuses noticeably slow, but does work. The IQ from that combination is also very good in conditions where the primary source of light is behind the camera. The same combination mounted on a 7D (APS-C camera, thus smaller mirror and narrower focus array) will hunt for focus but not generally succeed unless it is pointed at an area of very bright/dark contrast such as a bare light bulb, and then only certain focus points will acquire focus lock. Note that this is only the case with third party converters. The Canon extenders appear to use firmware to disable AF with f/8 combinations and AF won't even attempt to find focus with an f/8 combination mounted.
  • My Kenko convertor and every other one I've seen for Canon EF mount includes the same number of pins as my Canon EF lenses do. Since the Canon EF mount has no mechanical connections, without the pins there would be no way to stop down the aperture or use Auto Focus. My convertor correctly reports the aperture to the camera body. If I have an f/4 lens + 2X Kenko mounted the camera sees it as an f/8 lens. Apparently when the EOS system was developed back in the 1980s, the EF mount was designed to allow the provision for a lens with a manually set aperture ring on the lens. Thus the lens reports two different numbers to the camera: one that is the current aperture setting and another that is the maximum aperture of the lens. Third party converters and even lenses can fool the camera by reporting the lens as an f/5.6 lens set at f/6.3 (In the case of several third party zoom lenses that are f/6.3 when at maximum focal length) or even f/8.
  • Although I've never used the EF 100-400mm f/4-5.6 L IS, based on my experience with Canon bodies and lenses when combined with Kenko teleconverters, I would expect the 5DII/2X Kenko/100-400mm combination to attempt to focus and mange to succeed in brighter conditions. Due to the basic IQ of that lens when used bare, I would not expect the results from such a combination to be worth the trouble.

Test image using Canon 5DII + Kenko 2.0X Teleplus PRO 300 + EF 24-105mm f/4 L IS. Taken about 2-3 hours before sunset under a clear sky. One Shot AF. ISO 400, 210mm, f/8, 1/640 sec. AWB. Contrast and sharpening moderately boosted in post. f/8 test shot


I had a similar configuration (with a Canon extender). It worked in manual focus by default. With the "tape the contact" trick focus did work, but was only usable in bright light, anytime close to dusk, even with my poor technique I would switch back to manual focus.

  • My Kenko has pins and correctly reports the aperture to the camera.
    – Michael C
    Aug 7, 2013 at 22:50
  • @ChrisFletcher Without pins there is no AF. The Canon EF mount has no mechanical focus or aperture linkage, it is all electronic. The pins on the Kenko do not have to be taped for f/8 lens/converter combinations to attempt AF. Some have theorized the converter fools the camera into thinking it is an f/5.6 combination manually set at f/8.
    – Michael C
    Aug 8, 2013 at 0:47

Your best bet is to check the specifications of your intended teleconverter and your camera. A 1.4x teleconverter will cost you 1 stop of aperture speed, thus, if your camera is able to auto-focus at f/8, then it should still work as long as the teleconverter handles the necessary adjustments to preserve auto-focus capability (no all telecovnerters do, since it requires updating the aperture information sent to the camera.) Only a few cameras support AF at f/8 though, so it probably will be a problem.

Focusing will also be slower, though exactly how much slower depends on how good your AF sensor handles the f/8 focusing. You will also likely have fewer AF points available to you since typically only a few of them are setup to work at slower apertures.

  • In generally you would be using the extender to gain reach -- so assuming he is living out near 400mm the f/5.6 plus one stop will be f/8 which can only autofocus (without tricking the camera) on 1d bodies and now the 5dm3 in Canon land. Aug 7, 2013 at 15:32
  • @PatrickHurley - you are correct, I messed up on what 1 step was. I haven't ever worked with that high so I didn't think it jumped from 5.6 all the way to 8, but I see that is correct now. Updated my post.
    – AJ Henderson
    Aug 7, 2013 at 16:55
  • Tanks for answering.
    – Ruud
    Aug 7, 2013 at 17:33
  • Other Canon cameras will sometimes focus at f/8 depending on conditions. There is a difference between being rated to focus at f/5.6 as most of the older Canon cameras are and being firmware limited to f/5.6 like some of the newer Canon cameras are.
    – Michael C
    Aug 7, 2013 at 22:49

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