I'm a very amateur photographer with too much internet theory and not nearly enough field experience. I'm hoping someone with real experience can help me.
A few weeks ago I purchased a Cokin Pure Harmonie ND-X Variable circular Filter for my Nikkor 50mm 1.8 ( shooting with d750). This is my first ND filter and I planned on using it while on holiday recently. While it hardly got used while away, I have been using it since I have been back. Mostly down at the beach with my family, lens wide open, 1.8, sunny days.
The problem is, the images captured with this filter on are absolutely terrible (in my opinion, and no, I don't have any samples) . All of them have been very blurry bar none. I have tested the lens with and without the filter. Without the filter photos are always sharp, put filter on and..blurry. during testing camera was always manually focussed, on a tripod, different apertures used with multiple ND filter settings also used. Same result everytime.
Ok, so that was very long winded, sorry. I guess my point is, what Should I expect out of a $145 ND filter?. Should I expect a lot more than I am getting? As it is now I won't use it again. Should I just return it?. Being a novice I don't have the confidence that this filter is operating outside of the parameters of a $145 filter to tell the store that I want my money back/exchange .