When I am using the Altura flash on my d7100, I get one picture where the exposure is perfect and the next several are very under exposed. This only happens when the flash is on. When I am using the built in flash, I do not have a problem with exposure, however, I can only take 2-3 pictures before my camera "freezes" and it doesn't allow me to take anymore photos. I have to wait several seconds and turn the camera on and off again. I am currently using the kit lens but it happens with the 50 mm as well.