For trial and error might ...

Have the filter used in the course of my stay USA on a sunny day at the beach. Since I have not previously worked with filters, there were of course a lot to try. I did it then also relatively good job, despite popping Sun scan my wife with an open aperture. Furthermore, the graduated filter has given me a beautiful contrasting sky. However: I had a clear magenta cast on each image, also a slight blur over the entire image, even at the edges much stronger. The picture was still good, a little analog look had;)
But what does not change the fact that you simply can not use the filter if you want to make high-quality images. Why do I still give 3 stars? Because to me it was all clear, when I ordered a set of 18 Euro. I expected nothing else. Good filter costs just multiples! I wanted to see how this works as with filters, play around a little and then decide whether I need filters or not. And this purpose have complied with the said filter.