Nikon D780 DSLR Camera (Body Only) - Manual (Page 800)

754 Troubleshooting
Shooting
The display in the viewfinder, control panel, or monitor turns off
without warning:
Choose longer delays for Custom Setting c2 [ Standby timer ] or c4
[ Monitor off delay ].
The display in control panel or viewfinder is dim and
unresponsive:
The response times and brightness of these displays vary with
temperature.
Patterns appear in the viewfinder:
The viewfinder display may turn red when a focus point is
highlighted, but this is normal for this type of viewfinder and does not
indicate a malfunction.
The camera takes time to turn on:
More time will be needed to find files if the memory card contains
large numbers of files or folders.