@apvie Is it possible that your camera is setup for bracketing? I ask because you can obtain this exact sequence of exposures in manual mode by setting bracketing to "7F" and a step of ".3" with the "Auto Bracket Order" set to "MTR>under>over". Setting your shutter speed to 1/100 will yield the bracketed shutter speed sequence of:
1/100
1/200
1/160
1/125
1/80
1/60
1/50
then repeat.
Push the BKT button, it should say "0F" and have another value. If it says anything other then "0" before the "F", change it by rotating the rear command dial.
See if this solves your problem.


