hello,the vignetting issue may appear on your image.  

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. 

Look at e posture times longer than 10 seconds for the effect. The higher (darker) you set the filter, the longer your exposure times can be. Use an exposure app to dial in your exposure triangle info to get a correct reading with the filter. You definitely will be needing a tripod and use the self-timer to avoid any vibration. 

The BaK-4 Prisms have Phase and Dielectric Coatings for increased light transmission through the prism system for brighter images, increased contrast and resolution. 

It's about the zoom. It's about the diameter of the lense. If you look at the lense from the front, there should be a number. Like mine says 77mm