EF 100-400mm f/4.5-5.6L IS II USM Autofocus suddenly not working

[canonbirds]

Had this lens since Sep 2019 and worked beautifully for about 6-7 months and I've started noticing issues with it's AF for a couple months. 

I mainly shoot birds, f/5.6 to f/8. IS mode set to 2 on the lens for movement. AI Servo on the camera body. Av mode on the camera body so it chooses the shutter speed, I only change the f-stop sometimes and possibly the ISO but not much (maybe 2-400). Like I said, it worked great for months and months had no issues.

Now with everything being exactly the same and still using multiple point AF it will not consistently focus on the bird I'm aiming directly at and clearly have in my sights. Press the shutter halfway down, you can hear the motors in the lens trying to work and it just doesn't focus on the subject anymore. Every now and then I might get lucky based on proximity.

I called Canon today and was on the phone 20 minutes explaining the issue. He said I would receive Emails with directions on mailing the lens to them. He repeated my Email address back to me perfectly and I have not received any notifications.

Should I clean the lens without the caps off in any way? Should I do anything before sending it or taking it to repair? Any help anyone can provide is much appreciated. I've taken great care of it and I kind of expect a $2k piece of equipment to work properly. 

[kvbarkley]

So the lens is moving but not getting the right focus point?

That could be the camera. Does it work in Live View?

Does the camera work with other lenses?

In any case, you might want to send the camera with the lens.

[canonbirds]

Yes, I've used my 18-135 on the camera and the AF seems to work fine. It's a less capable lens so it's difficult to compare it much more than that. Doesn't have an ultrasonic motor like the lens in question has. I feel like these motors inside the lens are too loud but I could be wrong.

The 100-400 just doesn't want to focus lightning quick anymore on the subject and sometimes just doesn't at all.

Yesterday was the last straw when I was aiming the center focus point (I have multiple focus points set around the center point) at a Pileated Woodpecker (not a small bird) on the ground, not moving. The entire head, body and everything was blurry. I halfway pressed the shutter several times and it just couldn't focus. 

Side note: I have taught kids how to use robots and one of the sensors we use is the ultrasonic which uses ultrasonic waves that are sent out and bounce back to detect distance. It's essentially used for distance control in tandem with robot movement. I'm not a lens and camera expert but when a $2,000 lens says it has USM (ultrasonic motor) capability then I assume it uses the same idea for autofocusing on subjects, no? To me that is the aspect of the lens that is malfunctioning: the lens is having trouble with focusing because it can't correctly place the distance between it and the subject. But I don't really know, that's why I'm here.

Thanks for responding, appreciated.

[kvbarkley]

No, the ultrasonic refers to the tpe of motor, they also have STM and nano-USM now.

Lenses focus too far out for ultrasonic - though Polaroid used to have ultrasonic focusing.

The distance feedback comes from phase detection across the lens.

You still haven't said which camera.

Since LiveView uses contrast detection, it would be helpful if you tried that.

[canonbirds]

Sorry, I replied to someone else with the body. It's a 7D Mark II.

Not familiar with what you keep referring to as Live View? Maybe I am but I can't recall anyone mentioning this when I was first was learning how to use the camera and lens through tutorial and practice.

[kvbarkley]

It is when you use the sensor and not the viewfinder to compose and focus:

[canonbirds]

Thanks for that guide, I've never used Live View and couldn't imagine capturing birds like that but I could try. 

Was playing around with it at home earlier just to double check the AF is screwed up and it couldn't focus on a black remote 5 feet in front of me but a couple feet past that black, red, and blue items on my dresser it focused on perfectly fine. I don't get it. I need to reach out to Canon again to send my lens in. 

Thanks for your replies and insight.

[wq9nsc]

You stated earlier that you have always had the distance switch set on infinity and not full.  If the switch is still in that position, then it can't focus on a remote 5 feet away because it is restricted from focusing closer than 3 meters with the switch set to restrict the range.

As a quick test, set the camera to Av (aperture priority) mode and set your aperture to f8.  While looking through the viewfinder, press the depth of field preview button and see if the viewfinder grows darker.  The aperture should be wide open when focusing and if the aperture blades got stuck in a slightly closed position then AF becomes slow to impossible.

Rodger

[Waddizzle]

I totally agree with Rodger.  If the distance switch is set to 3-meters to infinity, then it cannot focus on a subject that is only 5 feet away.  You can confirm or deny this behavior by switching to One Shot AF mode.  Set the switch to "Full", and observe the  Minimum Focusing Distance spec.  I think it right around 4.5 feet.  You're cutting it pretty close.

In One Shot AF mode, the focus lock ball in the viewfinder may flash and then turn steady for a focus lock.  When the camera cannot lock focus, then the focus lock ball will blink very rapidly.  As a general rule, anything blinking in the viewfinder is an alert that you have done something wrong and the camera needs your help to resolve it.

[canonbirds]

That makes sense, thanks. I checked it at full and it does focus on the remote now. I also pushed the depth of field button and the viewfinder grew darker. What does that tell me exactly?

However, when I'm in the field, even yesterday with the woodpecker it was further than 3m away so I don't get why it wouldn't focus on the bird. Maybe there were too many shadows but the lens didn't have problems like that the first 6 months.