did a quick compare into single image .. for why we use GND and RGND
left … – no filter while foreground correct expose but the sky will look over
Center – with GND 1.2, the sky will be balance as reduce light go through on the top part but the horizontal level still look over due to the light source from there
right – the filter transit from center to top (darker at center) so managed to block more light at the horizontal level and maintain the details
there is no right and wrong in photography .. but using different filters will give you how your picture look like …..
and if you look for Lee Filter .. Singh-Ray … i may have some stock available