Problem with new D5100 found..

Not looking for any "proof".  Was just hoping to see the examples to study so that what might be learned could be passed on to anyone else in the future. In that way, it's easier to help the next person as this is a first...as far as I can tell.

Again, have not seen this so anxious to learn the cause. Please keep us updated if you find out.

It should stay the same (assuming tripod and perfect constant light for a scene match) as long as nothing changes like focal length..meter..base Iso...or picture control settings.  A few other things can do it but with ADL "off"...obviously not it.  One note:  were the shots CDAF (LiveView perhaps)  LCD brightness can affect it in this way as the camera will up the JPEG/Raw brightness setting to match what is seen on the LCD screen.  This is normally only a player though during outside bright daylight shots.  Another reason I was hoping to see the examples...Love a puzzle.

When you say reasonably close...they should be the same. How are you comparing?

If I use a tripod and the light does not change....my exposures are indeed matched "perfectly".  Here is an example used to show the affects of a filter (one pic has a filter on). All the shots were taken in sequence, of a test card. There's no reason they would not be exposure matched. Are you saying the light and scene wasn't actually matched in your original posts case? Good Luck going forward. Glad it has worked out.