Teleconverters and autofocus: What every wildlife photographer should know

In Gear by Jim Harmer25 Comments

Canon 60d autofocus teleconverter

Teleconverters and Autofocus

I received the following question via email and thought I should write a post here on ImprovePhotography.com to answer the question for the world.  Here's the question: “I'm looking at buying a teleconverter for my Canon 100-400mm L f/4-5.6 IS lens but I am having difficulty determining if the1.4x or 2.0x teleconverter will still allow for autofocus with this lens. I use a Canon 60d camera.”

Background Information

First of all, a little background.  DSLR cameras utilize two methods to focus: one is phase detection and the other is contrast detection.  Despite what photographers always argue in the blogosphere, BOTH autofocus methods require contrast in order to focus.  This is why it is difficult to focus on a large white sheet of paper.  Since there is no contrast, it is difficult to find focus.

The second piece of background information you'll need to understand teleconverters is that, no matter what aperture you set on your camera, the DSLR will use the largest aperture available to find focus.  It works like this: You set the aperture to f/8, but the lens stays at f/2.8 (or whatever the largest available aperture is) to focus.  Once you press the shutter button to take the picture, the lens quickly snaps the aperture to f/8 and then clicks the shutter.  This method allows the lens to gather as much light as possible for autofocus before closing down to take the shot.

What IS a teleconverter?

With that background, let's take a look at teleconverters and their unintended effects.   A teleconverter looks like a short piece of a lens that goes between the DSLR and the lens.  Its purpose is to magnify the focal length of the lens by 1.4, 1.7, or 2 times–depending on which teleconverter you buy.  Beginning photographers on a budget love teleconverters because it provides a long lens at a low price.  If only it were that simple…

The Drawbacks to Teleconverters

Teleconverters destroy image quality.  Without exception, teleconverters always make lenses less sharp. While more expensive wildlife/sports lenses can do a decent job of controlling a teleconverter, it still means losing some image quality.  If you have  cheaper wildlife/sports lenses (under $2,000), then a teleconverter will bludgeon your image quality to a bloody pulp.  Seriously, it's nasty.  Don't do it.

I'm not at all saying that photographers on a budget are left out in the cold, but I don't want photographers on a budget to waste their money on gear that won't give them good bang for their buck.

If you purchase a teleconverter made by a manufacturer other than the manufacturer of your lens, some data will not be transmitted to the camera. For example, if I use a Kenko teleconverter on a Nikon 400mm f/2.8 lens, some of the data that my lens usually passes to the camera to aid in focusing will not be sent.  Remember this when you go on Amazon and see that a 1.4x Tamron teleconverter costs about $130, while a Nikon teleconverter costs about $600.  Make sure to buy a teleconverter that is of the same brand as your lens.

Unfortunately, teleconverters reduce the aperture size.  A 1.4x teleconverter makes a lens lose 1 stop of light.  A 1.7x teleconverter makes a lens lose 1.5 stops of light.  A 2x teleconverter makes a lens lose two stops of light.  What does this mean?  It means that even the shortest teleconverter, a 1.4x, will transform an f/5.6 lens into an f/8!!!

So can I still autofocus with a teleconverter?

In the question that prompted this article to be written (a Canon 100-400 f/4-5.6 and a 1.4x teleconverter), the answer is no.  Autofocus will not work, or at least will not work well.  This combination will produce a 560mm f/8 lens.  Most cameras require somewhere between f/5.6 and f/6.2 in order to focus.  It depends on the camera, but f/8 probably won't allow for autofocus.

With this combination, manual focus is your best bet.  For untrained photographers, manually focusing a 560mm lens on a crop frame camera would be nearly impossible.  If you're wondering why it's tougher to manually focus a long lens, then check out this previous post.

There is a work-around to this problem by taping over three of the contacts on the teleconverter so the DSLR doesn't know you're using a teleconverter.  This situation will allow autofocus to work, but it will work erratically and improperly.

The bottom line

Don't buy a teleconverter to try and make your tele-zoom a supertelephoto lens.  The results will be disastrous.  Teleconverters should only be used with high-end fast-aperture wildlife/sports lenses.  Using teleconverters in other situations is a recipe for muddy image quality.


About the Author

Jim Harmer

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Jim Harmer is the founder of Improve Photography, and host of the popular Improve Photography Podcast. More than a million photographers follow him on social media, and he has been listed at #35 in rankings of the most popular photographers in the world. Jim travels the world to shoot with readers of Improve Photography in his series of free photography workshops. See his portfolio here.

Comments

  1. I have a Nikon DX body and my 300mm F/4D ED lens is my go-to for hiking and backpacking. That being said, how will using the TC-14e III FX affect my results? I know it will reduce me to a F/5.6. But, I also that the 300mm FX lens is cropped to a 450mm shot on my DX Body. Will the FX teleconverter ruin sharpness on this lens with the DX body? Since it is an FX TC, will it stay a true 1.4x or will it also be cropped to perceive a higher magnification? I haven’t seen anyone using an FX TC with and FX lens on a DX body in forums and am worried there may be a reason why. Thank you for any insight.

  2. I would recommend finding a good 300mm prime lens to use for wildlife. Then use a TC on top of that if you feel you need more length. Also, invest in a tripod (some come with a detachable monopod too!). The tripod (or monopod) will provide better stability producing a sharper image. Cameras can even pickup the press of a shutter release button. Also, I’m no pro, just have been doing a lot of reading and practicing. You can see some of my shots on Instagram @jacowitz_photo if you would like to see if there’s worth to my comment. 🙂 Thanks for reading and happy snapping!

  3. I had Canon setup: 5D Mark III, 100-400 USM II and 1.4 III extender.
    Autofocus did not work at first try. After upgrading 5D to latest firmware 1.3.4 (April 2017) the autofocus worked fine.

  4. Clean the contacts before giving up on converter-I was about to send a used 1.4 Canon converter back but cleaned the contacts with an eraser and viola it worked-on a 70 200 L 4.0 lens on a t2i rebel-much less weight and sharp photos. Not bad! May send my tamron 150 600 to sell-tired of the weight-get about 450x which is sharp.

  5. I sold my Nikon D3s and bought a little used Nikon D4. I set the camera up as I normally would and took it on a trip to Kraków in Poland (and on to Aushwitz) After viewing the images on the back of the camera I thought all was well and good. After viewing the raw files I realised that the camera was actually back focussing. It was a major over site on my part, so I went into the calibration menu and was amazed at what I found. The previous owner had almost identical lens collection to mine and calibrated each accordingly. These calibrations were MASSIVELY different to mine. I re-calibrated all my lenses and all soft/ out of focus areas were eradicated. Although I calibrated my 70-200, when I then matched it with my 2x converter, I found that it was much softer than normal and front focussing. I had to create a separate profile for the two separate optics. Maybe some of you posters might like to try a recal with lens and converter just to see if it’s mismatched in any way. I am usually pretty good when it comes to focus, but this one stumped me for a while til I realised my own
    mistake.

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