tjack wrote:
An ND filter is to a camera lens what a pair of sunglasses is to a human.
Actually it has no effect on color or sharpness, but it is perceived (appears)that way when the light is affected with the filter.
Here is another example shot tonight around 8:30 in evening with filter on and shot with wide open lens.
To my eyes the filter enhanced the colors even in the dim light and it did not suffer any in sharpness.
Sunglasses are often tinted though, I personally prefer amber colored lenses in my glasses, which are also polarizing. Between the polarization effect, and the warming effect, the world does look better with them... HOWEVER, a ND filter, as the name implies, is just that, "Neutral" meaning it shouldn't impart any color cast, save for some mild color shifts I see with some 10 stop ones, mainly due to IR.
If your ND filter is having an effect on color, (for good or bad) then I wouldn't say its a very good ND filter.
I've got B+W and Marumi ND's and as the name implies, they impart zero effect on the color of the scene, just reduce the exposure a given number of stops.
I bought them for my Fuji 23mm f1.4 and 56mm f1.2 (both sold/returned) because my XPro had a max shutter speed of 1/4000th and a base ISO of 200, so no way I could shoot those lens close to wide open without the ND.
Likewise, with my RX1 I often needed a ND as its leaf shutter was limited to 1/2000th at f2.0, but again, didn't get any color saturation effect etc from it, just reduced the exposure, which the camera compensated for.
What brand ND's are you using ?