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. 

Two sets of polarising filters with high transparency are used to control the amount of light entering the lens through the filters. 

1. The shutter speed can be freely varied to suit the desired effect without changing the aperture, while maintaining the optimum iso. 2. A large aperture exposure can be used to create a bokeh background effect while maintaining the same shutter speed 3. Even with a shutter speed of 1/8000 second, a maximum aperture of F1.4 or F1.2 can lead to overexposure. The ND2-400 can easily eliminate overexposure in such cases, preserving highlight detail. *As with zoom lenses, the adjustable ND has a wider range of applications and is suitable for a wider range of scenarios, so if you are looking for the ultimate in image quality it is recommended that you choose a fixed value ND. 

Two sets of polarizers with high transparency are used to control the amount of light entering the lens through the filter. 

Using Nikon Z 7 and Nikor 14-30mm Sline test, 14mm vignetting is not obvious, 16mm has no vignetting.