RF 100-400 Autofocus issues ONLY at 400mm

[brobin]

I've been loving this lens and using it for over a year, but this weekend, I started noticing an autofocus issue, but ONLY at 400mm

Within 10 ft: AF FAILS, MF succeeds
Between 10-20 ft: AF and MF succeed
Beyond 20 ft: AF and MF FAIL

Additionally, when the focus fails, there is a slight clicking noise if I listen carefully. Do I have a broken focus motor? Has anyone experience this before? I did not change any settings from the custom settings profile I have been using for 4 months.

Edit: other lenses focus perfectly fine, so I do not think the issue is the camera (R7). I'm taking it in to a local camera shop to see if they have any ideas as well.

[Tronhard]

If you are in the US, I would suggest calling 800-OK-CANON and having a chat with a technician.

[Waddizzle]

“ Within 10 ft: AF FAILS, MF succeeds
Between 10-20 ft: AF and MF succeed
Beyond 20 ft: AF and MF FAIL “

I can offer no explanation for your observations beyond 20 feet. 

The lens has a listed MFD of 2.9m, or roughly 9 feet. That spec most likely only applies to the minimum zoom setting.  

The lens is probably not anamorphic. This means that the focus is not constant as you change the zoom range. As you increase the focal length, then so will the MFD. 

If your lens is unable to focus beyond 20 feet, then remove any accessories like lens filters and teleconverters.  Retest again. 

[brobin]

This is the USM lens, mfd at 400m is just over 1 meter. But anyway, after talking to a tech at a local shop they recommended I send it in, likely a broken focus motor. Luckily I'm still under warranty

[FloridaDrafter]

---

@Waddizzle wrote:

"The lens has a listed MFD of 2.9m, or roughly 9 feet. That spec most likely only applies to the minimum zoom setting." 

---

Not that it helps the OP, but these are the MFD's for the RF 100-400 per Canon 🙂

"3.94 feet (1.2m) at 100mm
2.89 feet (0.88m) at 200mm
3.44 feet (1.05m) at 400mm"

One of the things I like about the newer Canon EF and RF tele lenses is the closer MFD from the older ones. IIRC, the EF 100-400L II has a similar MFD. I have both of these lenses and often use them to get near macro.

Newton