Due to the use of a polarising film to control the amount of incoming light, colour cast is a common phenomenon on all commercially available adjustable ND's. KF has minimised the effect of the polarising film on the colour cast by using a mature manufacturing process and perfecting its coating technology. *According to laboratory data, the ND2-400 has a bias value of around 290k, which is below the industry average of 500k. Does the ND2-400 have dark corners? Tested with Nikon Z 7 and Nikor 14-30mm Sline, dark corners are not noticeable at 14mm, no dark corners at 16mm.