« on: November 29, 2011, 02:43:17 PM »
Though the Singh Ray vari-ND is one of the best ND filters to have in your bag, it is not a gradient ND.
Rectangular resin filters by Singh Ray and Lee are fairly reasonable for the quality. Rectangular glass Schneider filters are appreciably more $$$. My experience with Cokin filters is the higher ND levels leave a purplish color-cast. As Neuro pointed out, you'll want to evaluate the hard vs soft edge available at the gradient transition line. As for the level of ND, there is no one overall solution here - the level you will need will vary with the lighting conditions/ratio between the bright areas and darker areas. Having a kit of three levels is usually sufficient.
Also, some photographers have success simply holding a solid (non-gradient) ND filter out in front of the lens and only covering half of the lens opening/front. By holding it out a centimeter or so and varying that distance, they can simulate hard or soft edged transitions. This is something you can try with your eBay kit you bought.