Canon has issued a product advisory for its new super-telephoto lenses, the EF 400mm F2.8L IS III and the EF 600mm F4L IS III.

Canon says the two lenses might experience a 'phenomenon where the exposure may flicker slightly if recording a movie with the camera shooting mode set to M or Av in combination with select cameras.'

According to the press release, an upcoming firmware update (version 1.0.8) will fix the issue with the affected cameras. In the meantime, Canon says there are two ways to avoid this problem:

  1. When shooting movies, set the camera’s shooting mode to P or Tv mode.
  2. When using the lens alone or with the EXTENDER EF 2x, set the exposure setting step to 1/2 or 1/1 with the camera’s custom function, even if the camera shooting mode is M or Av.

DPReview will update this article accordingly when the new firmware is released.