D800: AF tuned after repair gives incorrect results

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seldo New Member • Posts: 5
D800: AF tuned after repair gives incorrect results

Hello,

My D800 fell two years ago lens down, got a broken filter on my lens and I moved on. I was ok with the picture quality and never noticed anything.

A few month ago, it fell again, this time on the side. On the back, the metal part holding the screen got cracked above and below the buttons on the left side. The lens got a dent but still worked fine. I still took picture after that and it was still giving good results.

I brought it to my Nikon service center. They said that the back had to be changed (it was obvious) but also that the front part and the bayonet had to be changed as well. It isn't clear to me what was the front part, but I believe it is what Nikon calls the 'apron', which is the black part that is just behind the bayonet and goes from the flash/prism area all the way down to the bottom part. I wasn't so sure if it was caused by the last issue or if it was only from the first fall.

In this picture, they changed the black part and the bayonet system (that's from D700, but similar in D800).

I thought that it would be ok to get both repaired, so that the camera would be all fixed.

Sadly, I got the camera back with an AF not working. They specifically mentioned that AF had to be tuned again after changing the front part.

Now, I have no correct focus when I use the viewfinder. I've made tests at 1.5 meter, camera on tripod, taking pictures of a flat surface with details, a ruler on the table, to see if I could measure the shift.

I have a fixed focal Sigma lens (50 mm / ƒ1.4) that shows as much as 7 cm front focus (!) and a 70-200 ƒ4 that has ~2/3 cm front focus. Infinity is also wrong.

Both were tack sharp before the repair.

In short: all I get is blurry, and it is not due to my lenses since I know how they behaved just before the repair.

I couldn't find the Service Manual for the D800, but looking at the D700 Service Manual, Nikon doesn't mention that AF has to be tuned when these parts are replaced. It says AF has to be tuned if only PCB or AF sensor unit is replaced.

They also write about AF adjustement "AF accuracy adjustment (All the adjustments items will be made in order.) Caution: Whenever the AF sensor unit is disassembled/replaced or the main PCB is replaced, make this adjustment."

Also looking at the Service Manual, I do not understand why they would have had to touch anything related to AF, except possibly the knot for mechanical AF lenses (that is because it has to be adjusted so that it retracts well when removing lenses).

When I got it back I made some test photos (portrait, focusing on flat surfaces with particular details) and I determined AF was wrong. AF results were off when Live View photos were correct. If you are not aware, Live View AF works differently and I use it as my reference. I went back and explained my issue. They kept it for a day, said they made AF fine tune before giving it back to me. This is when I went to more detailed testing.

So, I know "don't touch a working system" adage, but it is now too late and my camera is unusable.

How can I get this fixed? What would you do as tests to show how things are wrong all along? Note that I can only give inputs using my Nikon 70-200 as they do not want to consider a 3rd party lens, which is harder since it is an ƒ4 and not and ƒ1.4, so there the DOF is more permitting.

I'm already getting sick of it and don't even want to touch the camera until all is fixed.

Unless I am mistaken, steps that weren't required were done and are most likely the cause of my issue.

Thanks,

seldo

P.S: when changing the back, the selector piece was either changed or moved to the new part. It now makes noise when it is moving, and feels stiff at times. However I was told it would get better with time as a new part had to be put behind and that it will soften as it gets used. I am not happy about it, but I will keep an eye on it. At least it is working, unlike my AF.

 seldo's gear list:seldo's gear list
Nikon D800 Nikon AF-S Nikkor 16-35mm F4G ED VR Nikon AF-S Nikkor 70-200mm F4G ED VR Sigma 50mm F1.4 DG HSM | A
Nikon D700 Nikon D800
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