lol silly me, was trying to screw it in the wrong way.
how do I know which orientation the filter is in? There is a silver mark on the filter. What does this indicate?
I think orientation of UV doesn't matter but it does with a polarzing filter.
You have to align the 'filter' 90 degrees to the direction of sunshine or, something like that.
Have used mine today and I just turn it until I have the desired effect. It does make a massive difference in reducing glare and reflection, if you haven't got one, get one!