I have three 77mm Variable ND filter now.

Tiffen 77mm Variable Neutral Density Filter-$150, purchased at b&h

FOTGA 77mm Slim Fader Variable ND filter-$15, purchased at ebay.com

Nature 77mm Variable ND filter MKII- around $80 (converted from Chinese dollars), purchased at China, This is the most expensive Chinese made Variable ND filter I find at China. However I do not see that it is being sold at ebay, amazon, etc here in united states.

All test were shot on tripod and in manual mode. jpg mode, standard setting. All three filters were set at its lowest ND stops (the brightest).

I am only comparing sharpness or resolution of each. I am not compare other parameter such as color shift, Vignetting, etc.

first test. canon 7d, 17-55mm f2.8 at 17mm f2.8

 

Click photo to view 100% to see the difference.

My bad. I lost track of which one is which…anyway they all produce very similar result of sharpness. Hard to tell difference.

canon 7d, 17-55mm f2.8 at 35mm f2.8

 

Click photo to view 100% to see the difference.

canon 7d, 100mm f2.8 macro at f2.8

 

Click photo to view 100% to see the difference.

As you can see. all filter produce excellent sharpness at wide angle 17mm (28mm in full frame). By 35mm (50mm in full frame), FOTGA lose some sharpness already, nature one look very good, tiffen one very close to no filter.

and by 100mm (160mm in full frame), FOTGA is very bad. nature one lose more sharpness but still usable, and tiffen again very close to no filter.

This is 100% pixel peep. I would think if people are use these filter for video shooting, the diffidence should be minimal.

I would say if you only use the filter for wide angle landscape photography, either filter produce excellent result. but as soon as you zoom in, the cheap FOTGA start to decline sharpness. the longer your focal length is, the worse the sharpness is. The Nature one keep sharpness quite well. The tiffen one no wonder the best. You can use it for photography and video with confidence.