It arrives today, actually, it should be faster if it's not Chinese New Year holidays.
This filter looked rather special, with a casual glance, you will see it's reflecting a lot of light, silvery looking, can be used as a mirror. If you looked at it from different angles, you will see purple color reflection. Looking through it with naked eye will show a very dim image.
It has a 8nm bandpass, centered at 395nm.
I've placed it side by side with a Baader IR-UV blocking filter:-
On turning it upside down, you will notice some difference. The filter glass really occupied the filter cell from both sides. I guess it's really consist of two different filters, I mean two pieces of glasses with dielectric coating and that's why it looked so thick. Maybe that's why Baader called it double stacked?
Sadly, we only got cloud for several days, so here is the first shot. It's taken with my Borg 45ED II, no diagonal is used, it's a stacked image of 16 raw images, each of them having exposure of around 3.5s:-
No more comment until I got chance to put it together with my Herschel Wedge with the sun!