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]

---

@jsfarnsw wrote:

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

---

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.

***********

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 

[jsfarnsw]

I don't think you've got that right.  The 70D uses a new Dual Pixel CMOS autofocus.  This system puts phase-detect AF over 80% of the image sensor's surface. 

Here's an article:  http://www.imaging-resource.com/PRODS/canon-70d/canon-70dDUAL_PIXEL_AF.HTM

[ebiggs1]

I only mentioned the tape method as a work around.  By your own admission, it isn't very good.  But f8 on my 1D Mk IV works very well.

[amfoto1 · Accepted solution]

---

@jsfarnsw wrote:

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

---

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.

***********

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 

[ebiggs1]

"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."

And you are correct.  The big 150-600mm Tamron and Sigam both report f5 to the camera.  Even though it is at 600mm and f6.3.  I hear rumors that Canon is testing a 600mm f6.3 prime.  It will interesting to see how they handle it.

[RobertTheFat]

---

@ebiggs1 wrote:

"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."

And you are correct.  The big 150-600mm Tamron and Sigam both report f5 to the camera.  Even though it is at 600mm and f6.3.  I hear rumors that Canon is testing a 600mm f6.3 prime.  It will interesting to see how they handle it.

---

Does it matter? Anyone who can afford one will already have at least one of the f/8-capable cameras. Of course any extender will throw it over the limit, but who needs an extender with a 600mm lens?

[amfoto1]

---

@RobertTheFat wrote:

---

@ebiggs1 wrote:

"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."

And you are correct.  The big 150-600mm Tamron and Sigam both report f5 to the camera.  Even though it is at 600mm and f6.3.  I hear rumors that Canon is testing a 600mm f6.3 prime.  It will interesting to see how they handle it.

---

Does it matter? Anyone who can afford one will already have at least one of the f/8-capable cameras. Of course any extender will throw it over the limit, but who needs an extender with a 600mm lens?

---

I don't know about that... We're discussing a $2200 Canon 100-400 Mk II here.

The Sigma "C" 150-600 and Tamron 150-600mm are both very affordable for such long telephotos. Under $1100 US.

Even the Sigma "S" 150-600 isn't too bad at $2000. That's pretty close to the price of the 100-400mm being discussed here, too. 

Any of those seem like bargains compared to the EF 200-400/4 with built-in, matched 1.4X ($11,000)  or an EF 600/4 Mark II ($11,500).

But I agree with you... on a crop sensor camera a 600mm lens is an extremely long focal length. Adding a 1.4X to it would be sorta nuts. Shooting through a lot of atmosphere can begin to have some effects even at 600mm. Even 400mm is a whole lot of lens on an APS-C camera.

Might be better to try to get a wee bit closer to the subject, instead.

***********

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 

[ebiggs1]

"Might be better to try to get a wee bit closer to the subject, instead."

Of course this is always the best solution.

"I don't know about that... We're discussing a $2200 Canon 100-400 Mk II here."

You don't know about, what?

[amfoto1]

---

@ebiggs1 wrote:

"I don't know about that... We're discussing a $2200 Canon 100-400 Mk II here."

You don't know about, what?

---

"Anyone who can afford one will already have at least one of the f/8-capable cameras..."

***********

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 

[ebiggs1]

Yeah, I guess, likely.

[jsfarnsw]

I stand as a case in point.  I own one camera, an EOS 70D, and one lens, the 100-400mm ii.  And a 1.4x iii converter.