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I bought a Nikon D750 during the 2017 Black Friday and the camera is just out of manufacturer warranty. I am having a weird issue with my Nikon D750. With the original 24-120mm Nikkor lens, I am seeing two issues.

  1. AF-C to AF-S selector is not working at times.
  2. When it does not work, I see that back button focus is also not working.

After several attempts, I was able to figure out that the lens was not mounted properly in these cases. Whenever I mount the lens and if I hear a click sound, everything seems to work fine. Sometimes, when I mount the lens, I do not hear the click sound and in such cases the AF-C to AF-S selector and the back button focus are not working. It is not just with the 24-120mm lens. I have a Yongnuo 50mm f/1.8 lens and a Tamron 28-300mm lens and I am seeing these problems with these lenses also sometimes.

I usually purchase extended warranty for high-value items, but unfortunately I missed to do it for my Nikon D750.

I am looking for some solutions or ideas to overcome this.

Can someone help?

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From your description, it sounds like you do not always fully rotate the lens to allow the mounting lock to engage (the click sound). Make sure you rotate the lens such that it is fully seated, causing the rotation lock to snap into place.

If you don't fully rotate the lens and lock it, then the lens communication electrical contacts are not fully or properly aligned. If that happens, the camera body cannot talk to, and control, the lens.

But if the lens does not feel like it is going to rotate further, above all, do not force anything when attaching or removing lenses. If the lens doesn't feel like it's going to properly seat, and it seems like multiple lenses exhibit this problem, then you need to have your camera body serviced.

  • Thanks, I will try that and see if that helps. Does cleaning the lens contacts on the camera and lens help? – Balaji Pooruli Jan 16 at 16:22
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    @BalajiPooruli Not if you aren't rotating the lens enough for the contacts to end up in the right place. The procedure for mounting a lens is in the owner's manual and includes "Rotate the lens as shown until it clicks into place." – Blrfl Jan 16 at 16:46
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    @Scottbb, I checked yesterday and it is the problem of not rotating it completely until I hear the click sound. I tried with all three lenses until I hear the click sound and I see that the focus selector and the back button focus are working fine. Thanks for your help. – Balaji Pooruli Jan 18 at 15:02

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