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?

[RobertTheFat]

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@jsfarnsw wrote:

Okay, I've tried the tape trick.  True, it's slower and less sharp than the normal AF without the TC.  However, it gets you close enough to manual focus from there quickly.  This probably means fewer missed shots when photographing wildlife. 

I'm not convinced that there's a technological reason that the 70D can't AF down to F8.  The sensor may actually be better equipped to handle this than other "pro" cameras.  Is Canon trying to sell "pro" camera bodies by intentionally disabling more capable "amateur" bodies?

Time for a firmware update.  Shame on Canon that we have to use scotch tape to do wat they are too timid to do in firmware. 

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Your speculation about the sensor's capability, even if true, is of doubtful relevance. Except in live view, the sensor is not involved in autofocus, because a) the shutter is closed and b) the mirror is in the way. What's most likely is that Canon's top-of-the-line cameras have a special high-gain autofocus sensor that replaces the less capable (and less expensive) AF sensor found in their lesser cameras. In the case of the 70D, it's hard to see what difference a firmware update would make.

[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

[jrhoffman75]

The Dual Pixel technology works in Live View only. There is no aperture limit in Live View.

[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.

[Thebellanger]

Hey folks how is everyone? I recently purchased an older Canon 500 mm f 4.5 zoom lens. I tried the 1.4 converter mk 3 and it did not autofocus on my 70D or my 5 D3 very disappointing any suggestions?

[jrhoffman75]

See this

Do do your cameras have an f/5.6 autofocus limit. 

[RobertTheFat]

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@Thebellanger wrote:
Hey folks how is everyone? I recently purchased an older Canon 500 mm f 4.5 zoom lens. I tried the 1.4 converter mk 3 and it did not autofocus on my 70D or my 5 D3 very disappointing any suggestions?

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You say it's a zoom lens, but you don't specify its focal range. Is it a lens that's 500mm at the long end, but f/4.5 at the wide end? If so, and if it isn't a "constant aperture" lens (i.e., one whose maximum aperture is the same throughout its zoom range), it will be slower than f/4.5 anywhere but at the wide end. But a 1.4 teleconverter subtracts a full stop from a lens's maximum aperture throughout its zoom range. IOW, it turns f/4.5 into f/6.3, and only a few high-end cameras can autofocus at above f/6.3. Which means that at best your 70D will autofocus only at the wide end of the lens's range. Your 5D3 can do a bit better; but unless your lens is f/5.6 or better at the long end, even it won't be able to autofocus over the full range. So you're probably going to be limited to manual focusing most of the time.

[ebiggs1]

Yet another reason why t-cons are a bad idea at best.

[jrhoffman75]

"Yet another reason why t-cons are a bad idea at best."

Not true - they can serve a useful purpose. One just needs to read the appropriate documentation and be aware of any limitations.

[jsfarnsw]

Ultimately, I sold my 70d and purchased an EOS 80d.  Problem solved. 

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@Thebellanger wrote:
Hey folks how is everyone? I recently purchased an older Canon 500 mm f 4.5 zoom lens. I tried the 1.4 converter mk 3 and it did not autofocus on my 70D or my 5 D3 very disappointing any suggestions?

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