To avoid dark corners, K&F Concept ND2-ND400 filters are designed in ultra-wide construction so the front side of the ND filter is one size larger than the camera lens. It is recommended to use a lens hood of a larger size. 

First, K&F Concept ND2-ND400 lens filter allows changing shutter speed based on the effect you want with the best sensibility and the same aperture. Second, K&F Concept ND2-ND400 lens filter allows creating a blurred background with a large aperture while the shutter speed remains the same. Third, K&F Concept ND2-ND400 lens filter is designed to prevent overexposure and maintain image purity and quality at the same time. *Like a zoom lens, the variable nd filters are suitable for multiple shooting situations. If you're looking for perfect image quality, a fixed ND filter is recommended. 

K&F Concept ND2-ND400 lens filter controls the amount of the light that enters into camera lens with two sets of polarizing glass of high transparency. 

The maximum aperture of an ultra-wide-angle lens below 24mm will have a slight cross shadow in the 1-5 gear dimming. The longer the focal length used, the smaller the effect of the cross shadow. There will be obvious cross shadows and vignetting in the large gear of dimming. If you continue to rotate the shadows, the shadows will disappear naturally, which is a physical phenomenon and not a product problem. 

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

In order to prevent vignetting, the ND2-400 is designed with an ultra-wide angle structure. The front port diameter of the filter is one size larger than the original aperture of the lens, so the lens cap needs to be one size larger than the lens aperture. For example, the 77mm ND2-400 Need to use 82mm lens cap. 

Due to the use of polarizing film to control the amount of light entering, color cast is a common phenomenon among all adjustable NDs on the market. KF relies on mature manufacturing technology and fine coating technology to minimize the polarization effect of the polarizing film. 

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