My Nikon D700 is suddenly really dark and underexposed, even when shooting indoors with all the lights on so it's really bright. For example, at ISO 400, 1/80, f/2.8 on a 24-70, or ISO 400, 1/125, f/1.8 with a prime lens, it's pretty much black. I need to set the ISO to at least 2000 to be anywhere near correctly exposed.
Have you by any chance recently turned off Auto ISO? Have you recently used negative amounts of Exposure Compensation? These and several other possible issue that could result in underexposed photos are covered in the questions linked below.
Nikon d5100 producing extremely underexposed images
Why am I getting dark black photos in P, S, and A mode on Nikon D5200?
Why is my Nikon lens suddenly extremely dark?
My photos are way too dark, must use 6000+ ISO inside
Wondering if my Nikon lens is broken
Nikon D5200 overexposed shots in "auto" modes
Only maybe one or more of:
Unlock and turn lens somewhat and then reseat.
Do this several times.
(Processor can get confused if contacts bad).
Leave several minutes.
Reset in Custom menu.
Reset in settings menu.
2 button reset - press and hold 2 green dot market buttons on top
(Qual on left, +/- on right.)
Master reset maybe>: Opinions vary. On the base at left rear by serial number the hole may house a reset button. On some Nikons it does. This may reset when held in with suitable pointed object (wooden toothpick or thin bamboo skewer usually safe). OT you may need to turn off, hold button in, turn on while holding button.
The latter is common on many systems. I tried it on a GPS unit and it wiped the program :-) this is a VERY unusual response.
Leave battery out for 24+ hours to some days.
Reinstall and try.
This is aimed at semi hard restart with discharge of capacitors. A well designed system will NOT need this and also not respond to it. It does work on some systems.
It's broken :-(.
Just found this. As it is by Nikon USA and does NOT mention D700 having a hard rest it's not encouraging if that's what is needed.