The majority of reversing cameras do automatically adjust to the light to allow for use in both bright sunlight and at night, but in terms of focus they tend to be fixed, as adding adjustable focus would make them considerably more complicated. A certain amount of flicker may happen if the outside light is changing, but if it is more significant than this it may be a problem with the unit itself. Whether this is covered under your warranty or not is another matter, but you may wish to get a second opinion from a BMW dealer or independent BMW specialist.