http://www.nikonchat.com/nikon-d90-kit/

I want to make a neutral density filter graduated from my Nikon D90. I have the kit lens (18-105mm)?
What kind should have and where I can get it?
Always buy good quality filters. Hoya, Heliopan, Singh-Ray, Tiffen are all good. As to where to get it. A camera store must have sufficient local or you can order online. B & H Photo is really good. Now what size to get. Look at the barrel of the lens. You will find a circle with a line through it. Next to that symble be a number. This is the thread size filter. Only for the filter to size. The 18-105mm lens has a 67mm filter size.
nikon d90 kit 18-105mm vr test video