Canon RF 100-400 Autofocus problem

[Len29]

Hello,

Does anybody have an issue with autofocusing in 400mm with this lens? When I extend the lens to 400mm and try to focus, the lens is not focusing. I have to retract the lens to 100mm and refocus. Only then autofocus works. It happens almost every time in any mode(M,Av,Tv or Fv). Camera Canon R6.

[rs-eos]

I don't own this lens, but just a couple questions to help troubleshoot:

• If you adjust the zoom just a bit less than 400mm, does it then work? i.e. does it fail only when exactly at 400mm?
• Any differences if the stabilizer is on vs off?

[Len29]

This is my second RF100-400 IS USM lens. Both behave the same, whether IS is ON or OFF. The autofocus is not working when I extend the lens to 400mm and it's out of focus no matter which button I use(back buttons or main release button). I tried to gradually zoom out while holding AF button and sometimes it start focusing at around 135mm. But most of the time I have to retract the lens to 100mm in order for lens to start autofocusing. 

[deebatman316]

If you have other RF Mount lenses do they work correctly on this camera.

-Demetrius

Current Gear: EOS 5D Mark IV, EF 16-35mm F/2.8L III USM, EF 24-70mm F/2.8L II USM, EF 50 F/1.8 STM, EF 85mm F/1.8 USM, EF 70-200mm F/2.8L IS III USM, 470EX-AI & 600EX II-RT

Retired Gear: EOS 40D & Sigma 17-50mm F/2.8 EX DC OS HSM

[Len29]

Update: The "problem" is solved. In the menu; AF; #4; "Lens drive when AF impossible" was OFF. When I changed it to ON, AF is working without any problem.

[rs-eos]

You shouldn't have to enable that setting to force the lens to focus.

This is sounding like you have an issue with the camera.  I would first reset all settings and try things out again.   If the issue remains, you probably should look at sending it in for a repair.

[Len29]

Thanks, You may be right. My other RF24-105 L f/4 lens is not doing this. But it's not 100-400mm zoom. I'm going to call Canon tech support tomorrow about this, will see what they say.

[Len29]

I called Canon tech support today regarding my issue. Their response was: Your lens and camera work within the normal operation. And they suggest using "Lens drive when AF impossible" and "Continue focus search: ON.

[jrhoffman75]

---

@rs-eos wrote:

You shouldn't have to enable that setting to force the lens to focus.

This is sounding like you have an issue with the camera.  I would first reset all settings and try things out again.   If the issue remains, you probably should look at sending it in for a repair.

---

That is exactly what the problem is. Long telephoto lens can get grossly out of focus so the camera can't "see" anything to start focusing on. I had the exact same problem with my 1D X MkIII. I had utilized some recommended settings from an online user. Lens wouldn't focus when I was trying to focus on ospreys flying.  If I manually focused to get the birds close then it focused OK.

If I switched out of the custom settings back to my basic it worked fine.  Took a while to sort out the problem.

[rs-eos]

Thank you for this added explanation, John!  I had assumed incorrectly about the default value of that setting as well.