How to view the filter coating surface and antireflection surface.
When installing the astronomical filter, it is usually coated on one side
Coated sheet, facing the direction of light coming in. On the other side are antireflective films to reduce reflection
How to distinguish the front and back of the filter.
It's mainly to see the reflection of the object. It's very practical and simple to see if there's any ghosting
The non ghosting is the coated surface, which is often called the front side
The one with double shadow is the antireflective surface, which is often called the back