Is it possible to auto focus with my 760D, 100-400 lens and a 1.4x converter?

[Sluggy]

I have just up graded to 760D and was wondering if there is any way to get my 100-400 lens to auto focus with a 1.4x converter?

[Waddizzle]

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@Sluggy wrote:

I have just up graded to 760D and was wondering if there is any way to get my 100-400 lens to auto focus with a 1.4x converter?

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Yes, but not very well.  I think your camera's AF operation is limited to f/5.6, or wider.  Refer to p119 in the instruction manual.  Adding the converter adds one f/stop,  Adding the converter will put you right at the limit.  AF speed will take a hit.

[Sluggy]

Thank you, that makes sense

[kvbarkley]

Is this a third party lens and converte? That makes it more likely to autofocus since the converter lies to the camera to get it to focus when the camera might refuse.

[Waddizzle]

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@kvbarkley wrote:

Is this a third party lens and converte? That makes it more likely to autofocus since the converter lies to the camera to get it to focus when the camera might refuse.

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I don't think it matters.  It seems Canon allows its' "L" lenses to break some of their own AF rules.  Some third party converters may not work, but it seems most of them manage to be compatitble.

A good example is how certain AF points can be cross point with lenses that are f/2.8, or faster.  Yet, "L" lenses with constant f/4 apertures are allowed to work the same way, despite not being f/2.8, or faster.

[diverhank]

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@Sluggy wrote:

I have just up graded to 760D and was wondering if there is any way to get my 100-400 lens to auto focus with a 1.4x converter?

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I am not so sure that the 760D can auto-focus at f/8.  Only a handful of Canon cameras can do this - 1D series, 5D Mark III, 7D Mark II, 80D...I haven't heard of the 760D (T6s) being able to do this.  This is new enough so I'm not 100% sure but I'm very doubtful.

The 100-400 at the 400mm FL range is f/5.6.  When you add a 1.4X, you lose one f/stop, making f/8 the lowest Av value.  Via firmware,  Canon consciously prevents their cameras to focus when f/8 is the lowest Av value except for those above Canon thinks are good enough to AF at f/8.

There are workarounds...you can tape 3 pins on the converter lens to fool the camera and AF will continue to work, albeit no so well - the reason why Canon disabled it in the first place.  3rd party converter basically do the same as taping by not reporting.  You can google the pin taping procedure easy enough if you want to try it.

Here is one: http://www.michaelfurtman.com/taping_the_pins.htm