teleconverter 1.4x iii autofocus problem

[jsfarnsw]

my 100-400 ii won't autofocus with a 1.4x iii on an EOS 70D.  When I install the teleconverter, the camera automatically switches from AF Servo to M Focus.  

Solutions?

[amfoto1 · Accepted solution]

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@jsfarnsw wrote:

Thanks everyone.  I did not realize the AF systems required that much light to work properly. 

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AF needs adequate light to work reasonably fast and reliably.

Do an internet search about teleconverters and taping up some of the contacts. This "fools" the camera into not realizing the converter is there, so that it will still try to AF the lens. Just don't expect focus to perform very well. It will be slower and in lower light situations or with low contrast subjects it may hunt a lot and even fail to achieve focus. There's a reason Canon sets a limit and turns it off, when a lens/teleconverter combo exceeds the rated AF capabilities.

You'll have to find a website where someone illustrates which pins to tape up. I haven't done the tape trick myself... I simpy don't bother with TCs on lenses where it would exceed the light levels, or in a few cases I just manually focus (500/4 with a 2X on it, for example).

7D Mark II (not the original one), 5D Mark III (not the II or original), all 1-series (film and digital) and the EOS-3 film cameras are "f8 capable", meaning that they can still AF (mostly with one center AF point only... 5DIII can use a small group of points in the center I believe) when a lens + TC makes for an f8 or larger aperture. All other Canon cameras, including 70D are "f5.6 capable".

The 100-400mm is f4.5-5.6 already... so adding even a weaker 1.4X, makes for an f6.3-f8 combo that exceeds your camera's design capabilities. But some folks manage to make it work to a limited extent with a few small, carefully placed pieces of Scotch tape!

Note: There are a few third party lenses that are f6.3 even without any TC, yet still AF... probably by similarly "fooling" the camera.

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Alan Myers
San Jose, Calif., USA
"Walk softly and carry a big lens."
GEAR: 5DII, 7D(x2), 50D(x3), some other cameras, various lenses & accessories
FLICKR & EXPOSUREMANAGER 

[amfoto1]

Did you buy a Canon EF 500mm f/4.5L? (Not a zoom, but a lot of people use the term when they actually mean "telephoto".)

If so, when you add a 1.4X Teleconverter to it, the combo is an effective 700mm f/6.3.

70D is "f/5.6 limited", meaning that it's AF system will not be able to autofocus that combination.

But 5D Mark III is "f/8 capable" and should be able to autofocus the combo. However, this feature is limited to one or a few of the AF points at the center of the array. Check your user manual for more info.

Also search the internet for info about taping up some of the contacts on the teleconverter, so that it's "hidden" from the camera. After doing that, you should be able to get the combo to autofocus on both the 70D and with all the points of the 5D Mark III. AF might be a bit slower and may hunt at times, especially in lower light or lower contrast situations. But it should work.

The only down side to the tape trick is that the EXIF metadata willl show the focal length of the lens alone (500mm in this case), because the camera doesn't "know" the teleconverter is there.

EDIT: I just noticed the EF 500mm f/4.5L isn't on the 1.4X III compatibility list (see above). Not sure if it was just omitted because it's a fairly old lens, or if there is actually an incompatibility between the old lens and the latest-and-greatest teleconverter. If there's a problem, you might try a Kenko 1.4X instead... Ther're pretty close to the image quality of the Canon and considerably less expensive. The cheaper Kenko "MC-4" 1.4X is sharp in the center, but less so in the corners... so might be a good choice to use on an APS-C camera like your 70D. But on the full frame 5DIII, you might prefer the slighlty higher priced Kenko "Pro 300" 1.4X, which has better edge to edge, corner to corner sharpness. 

***********

Alan Myers
San Jose, Calif., USA
"Walk softly and carry a big lens."
GEAR: 5DII, 7DII (x2), 7D(x2) some other cameras, various lenses & accessories
FLICKR & EXPOSUREMANAGER 

[ebiggs1]

The fact that they have some small benefit doesn't make them a good idea. They mostly cost more than they give.

[Thebellanger]

My friends 7d had no problems focusing. I am saving for a newer 500mm f/4

[Vonnancy]

Mine does the same. What is the fix?

[ebiggs1]

"What is the fix?"

Probably to start your own thread. This one is 4 years old and not likely to get many answers.

[jsfarnsw · Accepted solution]

What a surprise to get notifications that someone was resurrecting this zombie thread!

The fix for me was to sell my EOS 70D and purchased an 80D, which will autofocus at f/8.  I have since added a 90D to my kit and I've replaced the EF 100-400mm with a 400mm f/4 DO. The only thing I kept from those days was the 1.4x teleconverter. Amazing how equipment upgrades can solve an autofocus problem.