"D5100 - AE lock (Hold) turning off after pic review"
Hi there. A little doubt here.
It seems some Nikons does not behave this way. Others - like D5100 and D3100 - do. Also it seems this is a kind of "problem" easily solved via a firmware update. But Nikon got to know about it or even accept the "problem" before releasing an update.
If you have a D5100 or a D3100 try this:
Set AE lock to hold mode. Set auto meter-off to 1 or 30 minutes. Set image review timer to 4 or 8 seconds.
Now, half press the shutter to focus, press AE-L/AF-L button to lock and hold the exposure metering. Take the photo.
The normal (that correctly happens in other Nikon models) behavior is that even after the image review turn off automatically the AE-L (Hold) should continue to be ON to the be used in the next shot.
But if you do not half press the shutter before the review image turn off (or have a long image review timer on or even have it totally off) the AE-L (Hold) is erroneously turned off. The timer is set to hold the AE-L to 30 minutes. So It should be on for 30 minutes. Even if the user have review image on.
Am I being clear?
Can you test this with your cameras and post here the results?