I have heard of problems with the dioptre adjustment not working on the Nikon D600/D610 and wondered just how common this is, and if Nikon are doing anything about it. The problem is that when attempting to adjust the dioptre, nothing happens and the view is 'out of focus' throughout the rotation of the adjusting wheel.
I have just had to return a brand new D610 with this problem, having given up various attempts to achieve eyesight correction.
With the camera on autofocus a perfectly sharp image is created, so no problem with the camera's focussing.
I am hoping that a replacement camera will not have the same fault.
Meanwhile, I would be interested to hear from others with a similar experience - and what the outcome was.