The problem occurs in 1/50 or 1/60 , which is the normal speed for shooting Pal or NTSC footage (in 24p or 25p).Good news regarding 25P! However, I was struck by the comment about black banding and pilpop's response to use 1/30 or 1/25 shutter speed to avoid this. Just to clarify: What shutter speeds actually cause this problem?
I have also the problem whne in low light and underexpose.
You need fast lens and keep the exposure high (as high as you can).
You can sove this problem (if you have it) by turning down the shutter speed to 1/25 or 1/30 , but then you have more motion blur in moving objetcs.