Jittery focus on 200-400 VRI

[Randy Stout]

I was looking at a 200-400 today with the intent of purchasing it for marching band performances, which I cover for the High School.

I mounted the D500, and when trying to focus against any target, at various distances, the lens would constantly focus back and forth a short distance.  The lighting was bright, and I tried a variety of targets, didn't seem to make any difference.  D500 , back button focus.  I have never had a Nikkor that would do this under such good lighting conditions.  It would never settle on a final focus point.  The focus confirmation dot would go on and off as the lens focused back and forth past accurate focus.

I dismounted the camera, looked at the contacts on the mount, seemed OK.  Unfortunately, it was a situation where I couldn't play with all the settings or try a different body.  I rechecked the D500 when I got home on a different lens, its usual fast and accurate self.

Would appreciate any thoughts you might have. Needless to say, I didn't purchase it.  Hopefully it is something minor, but I was worried that perhaps the AFS system was failing.

Thanks

Randy

[Ilkka Nissilä]

Is it a used lens?

What was the distance range where this was happening? I felt when testing this lens that it would hunt especially with grass backgrounds and subject some distance away but behave quite well at close distances.

[Randy Stout]

Ilkka:

Thanks for the response.

Used lens.  Focused on a variety of objects between 10-30 meters.  Many with high contrast.

Randy

[Ann]

Perhaps the contacts on the lens itself need a good cleaning with anti-oxydent; or the lens was in need of a visit to Nikon Service for general lubrication and maintenance?

I have this lens and it focuses well on normal targets. It only seems to have a problem when used with a TC or on distance objects under hazy conditions.

[paul_k]

I'm the long time owner/user of a 4/200-400 VR I (got mine in I think 2006) and used it extensively for years shooting surf, and since I don't do that any longer, nowadays for shooting catwalk, initially on a D2X, then on a D3 when that became available, and nowadays on D800's

Don't own a D500, so don't have in depth experience with the improved MultiCam 20K AF
Recently played with a D850, in particularly tried my hand with  the AF, but that was too short to be able to make a serious evaluation of it.
Did seem an impressive improvement over the CAM 3500 AF module in the D3/D800 though, despite the short time I was able to experiment with it
.
Don't recognize the jittery AF issue you describe, but must say that based on the description it doesn't seem be a related to the AFS motor  itself problem; agree with the suggestion it might simply be a matter of dirty contacts

That said, given the high number of AF points of the Multicam 20K AF module, might it be a consequence of the camera having, as a consequence of the selected number of AF points (as in the f1 Custom Control Assignment setting) ?
Even with the the lower AF points Cam 3500 AF module, in certain situations and with certain settings, using all 51 points can confuse the camera and cause somewhat erratic AF behaviour/jumping around

Have run into a 'jittery image' problem with this lens in the past.
Turned out that was due to a faltering VR motor, the consequence of years of shooting surf in the rain while constantly being covered with salt water spray without any kind of (rain) cover for lens nor camera.
In the end some of that salt water got inside the lens and corroded the electric contacts of the VR motor inside the lens, making it jump rather then move fluently while stabilizing the lens elements concerned
Got 'fixed' when NPS repair disassembled the lens for a repair estimate and, after I declined the repair, reassembled it, in the process cleaning those contacts

On a side note, as someone who has used/uses the lens most of the time for shooting subjects  moving (fast) in sometimes erratic patterns
I do wonder why you use back button focus when shooting what appears to be static subjects, even if at varying distances

I personally always keep the AF on the release button, use the AF back button to 'pre focus' in anticipation of a shot I think I might take to shorten the 'reaction' time for the lens to focus when I do take the shot
Or in situations, as described in another reaction, where eg due to atmospheric conditions combined with far away subjects, the camera might have a problem finding a point to focus on, or the AF of the camera is put under more pressure due to use of a TC

my two cents

[Randy Stout]

Thanks everyone for the input.

Paul, I am mainly a bird photographer, so back button focus all the way for me.

The owner of the lens took it home and tested it on his DF, D700 and D300, and it worked fine.  (He hadn't used it for a while, so he wasn't certain it was still OK, after my problems with.)

I am use D-25 for the focus pattern, and wonder if somehow that isn't compatible with the older lens?

I will see if I can borrow it for a bit and play with different focus combinations.

Thanks again!

Randy

[Ann]

Dynamic AF behaviour has changed slightly in the D5 and in the D500 as well.

It self-adjusts focus faster than it did before and it depends on the User being able to keep the primary focus point on the subject.
Setting a Delay may make this easier, especially with longer telephoto lenses.

There was a long discussion over at Fred Miranda about this.

I actually prefer the new Dynamic AF behaviour but others have found it difficult to manage.

Dynamic AF never "tracked" (the photographer has to move the camera to keep the target under the primary FP) but because it responded more slowly on earlier cameras, people thought that D25 was tracking.

3D Tracking is the mode to use if you want the camera to do the tracking.

Steve Perry explains it well here:
https://backcountrygallery.com/understanding-nikon-af-modes/

[BruceLeventhal]

I am a bit late to the party here, but I have 3 D500's and a 200-400mm f/VRI that I use for wildlife photography and I do not experience a "jittery" or hesitating focus. In general, the lens locks on very well unless I have a low contrast subject. I mostly shoot single point AFC and group AFC. When I do use D25, focus is based on my initial focus point and I will lose focus if I do not keep track of my subject.

Like others have suggested, you might want to clean the contacts on the body and the lens. In addition, it is possible that you have a dust bunny on the AF sensor below the sub-mirror. If this is the case, you might need to go into the sensor clean mode and blow off the AF sensor.

cheers,
bruce