AF on a Nikon 400mm f2.8G AFS VR chatters and stops working

[Sören Hese]

Dear community,

maybe someone knows how to deal with this or has experienced something comparable.
I am using a Nikkor 400mm AFS f2.8G VR heavily on my shootings (sports) on a D810 and D850 and now recently the lens just stops focusing accurately after approx 600-800 shots and starts to move the focus back and front with high speed - creating a chatter kind of focus movement with back and front focus and just doesnt lock focus anymore at all. When I go on trying to focus the lens ultimately just gives up and stops focusing. I have to put the lens aside and switch to my 300milli to move on with the shooting and after a while when I pick the 400mm up again it seems to work again for some dozens shots until the problem fully reappears.
It is not fixed to a specific camera body/lens combination and also switching off/on wont help. The lens VR is always off and my setup on the D850 is on AF-C 3D.
However changing this has no impact on lens behavior. It seems to be a kind of fatique effect - maybe linked to the AFS ring motor? The lens has 600k images done. The problem is hard to reproduce for NPS repair or an insurance case since the lens works like a charm the next day ... .

I would be grateful for any ideas and if someone could drop some lines from her/his experiences.

Thxs so much. Best! Sören   

Attached a shot from this (otherwise) great lens

[Sören Hese]

For those interested: Nikons diagnoses was that the SWM unit is dead - so I will let them replace the motor. Best wishes! 

[Birna Rørslett]

How many years did the motor unit last? Getting curious here.

[Gone]

I had a similar issue with a 28-70 f2.8 - it turned out to be the magnetic focus pickup.

[ColinM]

Nikons diagnoses was that the SWM unit is dead - so I will let them replace the motor.

Are they doing this under warranty Sören?
For a professional tool like this (allowing for your reasonably high usage) I'd have thought many people would have been disappointed in such a fundamental part failing like this.

[Sören Hese]

Lens is from 2009 (water sports, soccer) the lens has approx 600k shots done. The last 6 years also pretty much heavy use on water - so maybe the lens also had too wet conditions here and there - although always used with lens coats from Aquatech.  Working on small RIBs - motorboats - is always a bit on the challenging side for equipment but shouldnt damage the SWM.   
 

[Sören Hese]

Are they doing this under warranty Sören?
For a professional tool like this (allowing for your reasonably high usage) I'd have thought many people would have been disappointed in such a fundamental part failing like this.

no warranty anymore - but maybe my photo equipment insurance will kick in. Yes this is kind of a major failure - but this lens has paid for itself well the last few years. 

[Erik Lund]

I had a similar issue with a 28-70 f2.8 - it turned out to be the magnetic focus pickup.

I agree, sounds like the Encoder; magnetic strip and the reading head needs a cleaning.
Similar to the first video linked in my recent post: https://nikongear.net/revival/index.php?topic=10540.msg186335#msg186335

[Sören Hese]

I agree, sounds like the Encoder; magnetic strip and the reading head needs a cleaning.
Similar to the first video linked in my recent post: https://nikongear.net/revival/index.php?topic=10540.msg186335#msg186335

Sounds as if I should put the Nikon technician on that track, is this a complex repair or service? The SWM replacement is at 760 € and half of it is cost for labor  - so the SWM itself costs 310+vat. I think it might be more cost efficient to go for the new SWM directly. On the other hand this lens is just a monster compared to its new variants.

[Erik Lund]

It’s just a matter of cleaning the encoder and encoder strip with appropriate liquid and cotton swabs. SWM is not the problem imho

[Sören Hese]

It’s just a matter of cleaning the encoder and encoder strip with appropriate liquid and cotton swabs. SWM is not the problem imho

Hej Erik, thxs, I will talk to the technician directly but this strange slow recovery of functionality makes me a bit skeptical. It feels as if a key component is just dying. However I will have to repair the lens. I cant afford to buy a f2.8 replacement lens right now and once you get used to this creamy f2.8@400mm background blur its hard to move to something else.   

[Gone]

The tech should clean and lubricate everything in the lens if they are going to service/repair it.  Best to just let them do the job.  My 28-70 came back absolutely pristine for the sum of just under £200 inc shipping.

[Sören Hese]

Dear all,
had a longer discussion with the technician from Nikon Munich/Germany and he explained in detail how the ring-SWM is aging. It seems to start with a squeaking sound that indicates the start of stronger friction within the motor. This leads to increased power consumption of the lens. With increased SWM-age this problem slowly escalates.  When the needed power cannot be provided by the camera anymore the lens SWM just stops working. The problem progresses and escalates with SWM-age - ultimately making the SWM useless or only usable for very short time frames. This overall fits to my experiences with the lens:  squeaking AFS sound and mal functioning after some time of intensive use.  My impression is that the problem becomes apparent in its early development status only when the lens AFS is heavily used. For casual shootings with long pausing in between shootings this problem likely surfaces much later in the life-cycle of such a ring-SWM.
However I dont exactly understand what causes the increased friction within the SWM to develop over time. I read on dpreview that one could clean the SWM stator/rotor manually - well - clearly far beyond my level of mechanical expertise. ... but maybe there is just some oxidization at work inside the SWM.   ;-)  best! Sören

[Erik Lund]

I did not notice you stated that your lens is squeaking?

I completely agree, that if the lens is squeaking it's the SWM.
The encoder is not aging, it's getting dirty just like an old cassette deck! The encoder is not touching the encoders-trip, magnetic strip.
It's just tiny particles accumulating over time, disrupting the signal.

[Sören Hese]

I did not notice you stated that your lens is squeaking?

I completely agree, that if the lens is squeaking it's the SWM.
The encoder is not aging, it's getting dirty just like an old cassette deck! The encoder is not touching the encoders-trip, magnetic strip.
It's just tiny particles accumulating over time, disrupting the signal.

yep I didnt mention - mainly because I got used to it - the lens made more squeaking than normal - but I realized it only fully when my new 70-200 arrived,  ... that this is odd.
After 13 Years of heavy use (one corona year can be subtracted) - its kind of disappointing that the SWM is just giving up but given the high price of the 400mm, I can somehow digest that now.  Best and thxs for commenting, and another shot from that lens
Sören