7.4mm 

Hello, the VND filter is 9 stop adjustable. 

Because K&F Concept ND2-ND400 filters adjust the amount of light that can pass through polarizing glass, color cast cannot be avoided with all variable ND filters on the market. However, K&F Concept variable ND filters are made with the best coating technology that reduces the effect of the polarizing film on the image color. *Based on our professional test, the color cast of K&F Concept ND2-ND400 filters is around 290,000 while the industry standard is 500,000. 

First, the K&F Concept ND2-ND400 lens filter allows you to change the shutter speed based on the desired effect with the best sensitivity and the same aperture. Second, the K&F Concept ND2-ND400 lens filter allows you to create a blurred background with a large aperture while keeping the shutter speed the same. Third, K&F Concept's ND2-ND400 lens filter is designed to prevent overexposure while maintaining image purity and quality. *Like a zoom lens, the variable final filters are suitable for multiple shooting situations. If you are looking for perfect image quality, a fixed ND filter is recommended. 

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

Tested with Nikon Z 7 and Nikor 14-30mm Sline, dark corners are not obvious for 14mm and no dark corners for 16mm. 

Yes, the 2 in 1 filter is HD imaging. 

Hello! To use a lens cap or hood with the variable ND filter, you need to increase the filter size for them by one standard filter size, as the filter's outer glass is larger to avoid vignetting. eg For this 52mm filter you must use a 55mm lens cap or a 55mm lens hood.