I plan to buy a Nikon D80 camera, a Nikon 18-200mm F/3.5-5.6G ED-IF AF DX VR Lens, a Z-Pro filter holder (made by Cokin) which holds 4X6" filters, and some Singh-Ray soft and hard graduated neutral density ("GND") 4X6" filters. The above-noted lens has a 72mm ring mount. Is it possible to kill two birds with one stone by using one-half of each hard Singh-Ray GND filter as a full neutral density filter? In other words, is it possible to completely avoid the clear and transition areas of the filter with this lens? It looks like it would be a tight fit. Also, can anyone recommend a 4X6" GND filter from a different manufacturer? Singh-Ray and Lee are the only companies that I know of that make this size GND filter. I am new Nikonian member, and I don't know much about photography, so I would appreciate any advice.
I too have the Cokin Z-Pro holder and a Cokin Grad filter. I think you could do as you describe. Your front filter is 72mm, roughly 3inch, and that is also where the divider line is, so this should work, especially at the longer end of the lens.